Dr Mohsen Khalily

This paper presents a dual-functional Simultaneous Transmission and Reflection Reconfigurable Intelligent Surface (STAR-RIS) that integrates communication via reflection and computation/sensing via transmission within a single aperture. When an incoming wave impinges on the STAR-RIS, part of it is reflected for communication, while the transmitted portion, shaped by a lens phase profile, performs Fourier transformations in the k−domain enabling computational tasks. A coding metasurface approach is used to create a linear phase gradient in the reflection space and a lens phase profile in the transmission space. This enables tailored beam patterns for reflection and computational tasks, such as Fourier transforms, for accurate angle-of-arrival estimation and sensing applications. To validate the concept, a STAR-RIS with side-by-side reflection and transmission arrays is designed, fabricated, and tested at 26 GHz.

This work introduces an innovative miniaturized transverse electromagnetic (TEM) waveguide design, which is 60% smaller than conventional metal waveguides. The proposed waveguide offers two distinct electronically reconfigurable passbands well below the cutoff frequency. This has been achieved by using sidewalls composed of reconfigurable artificial magnetic conductors (AMC), optimized to operate at 3.51 GHz and 4.37 GHz. By replacing the metal sidewalls with an AMC structure, a TEM mode can be sustained within the confined space enclosed by the waveguide structure, which otherwise would not exist in a conventional metal waveguide. This eliminates typical cut-off frequency constraints that limit the size of conventional waveguides, thereby enabling a significant miniaturization of the waveguide design. The work also proposes a reconfigurable AMC design whose operating frequency can be dynamically adjusted by applying or removing a direct current (DC) bias across the integrated PIN diodes. Additionally, this work utilizes 3D printing technology to fabricate a functional waveguide, highlighting the design’s compactness, cost-effectiveness, versatility, and fast prototyping capabilities for a wide range of microwave applications. This study therefore demonstrates the potential of using reconfigurable AMCs for compact and versatile waveguide designs that can be 3D-printed for various practical use cases and modern microwave applications.

Reconfigurable intelligent surfaces (RIS) are positioned as one of the key enabling technologies for 6G networks as they can provide ubiquitous coverage for areas with blocked line-of-sight (LOS) links. However, to be successfully integrated into functional networks such structures will require the addition of sensors and other radio network elements, thereby resulting in a multi-functional RIS (MF-RIS). These structures are expected to be deployed for integrated sensing and communications (ISAC) and radar and communication coexistence (RCC) in 6G, which will enhance the performance of radio communication and enable a smart wireless environment (SWE) that is programmable and self-reconfigurable. This survey provides an up-to-date summary of the state of the art. It considers applications for MF-RISs and the challenges associated with their deployment.

This paper presents wideband channel measurements for indoor Non-Line-of-Sight (NLoS) fixed links operating at sub-Terahertz (sub-THz) frequencies (92-110 GHz) with single scattered reflections. Seemingly "smooth" surfaces generate substantial internal multipath causing frequency selective scattered reflections owing to the short wavelength. Unlike specular reflections, no single well-defined reflection point aligns the incidence angle (θi) and reflection angle (θr) to form the lowest path loss. This means that the scattering effect of the reflective surface gives reason to search for the best angular alignment of the Receiver (Rx) antenna given a specific angle from the Transmitter (Tx) antenna. The wideband effective Radar Cross Section (RCS) is derived and computed based on the bi-static radar equation, which specifically accounts for the effect of alignment angle on the defined frequency selective RCS. The measurements reveal alignment-variant angular scattering from large-scale discontinuities such as wall partitions, television screens and metallic reinforcement studs, offering valuable insights for the design and deployment of future wireless communications systems operating in the sub-THz band.

A polarization-insensitive circular reflectarray antenna (RA) for long-distance wireless communications is investigated. By combining patches, dipoles, and rings, a polarization-insensitive unit cell is achieved. With a phase variation of around 314 • between 30 GHz and 32 GHz, a circular reflectarray with a radius of 400 mm is built. Simulation results indicate a maximum realized gain of 27.6 dB at 30 GHz.

This article investigates the unexplored potentials of vortices or orbital angular momentum (OAM) beams using the low-cost and high-gain dielectric reflectarray antennas (RAs) at the terahertz (THz) band. It proposes a paradigm to enable 3D beam-steering or OAM multiplexing by a single structure via tilted OAM beams. That, in turn, requires reaching the maximal attainable angles either to send multiple beams to different receivers or to focus the OAM beams of different modes in a desired direction. For this reason, two concepts are addressed in this work: (i). generating a single 3D steered OAM beam and (ii) producing multiple off-centered OAM beams with different modes. A volumetric unit cell is adopted to be accurately tuned through the aperture to steer the generated beams towards the desired direction(s). The proposed paradigm can be utilized to produce RAs with beam-steering or OAM multiplexing capabilities as candidates for THz indoor communications.

This paper demonstrates the ability of the reflectarray antenna (RA) to perform orbital angular momentum (OAM) beamsteering with low divergence angles at the fifth generation (5G) millimetre-wave (mmWave) bands. To provide steered OAM beams, it is necessary to regulate the scatterer’s geometries smoothly throughout the focal area to follow the required twisted distribution. The traditional numerical method to compensate for the phase is modified to enable the 3D scanning property of OAM beams, so it is possible to avoid the feeder blockage and produce high-gain steered OAM beams. Likewise, reducing the inherent beam divergence of OAM beams can be obtained by examining the most satisfactory phase distribution of the scatterers by fitting the focal length. The simulated radiation pattern is validated by the measured radiation pattern of the fabricated RA in the frequency range between 28.5 GHz and 31.5 GHz.

A polarization-insensitive circular refiectarray antenna (RA) for long-distance wireless communications is investigated. By combining patches, dipoles, and rings, a polarization-insensitive unit cell is achieved. With a phase variation of around 314° between 30 GHz and 32 GHz, a circular reflectarray with a radius of 400 mm is built. Simulation results indicate a maximum realized gain of 27.6 dB at 30 GHz.

This paper presents spatio-temporally resolved wideband measurements of Sub-Terahertz (Sub-THz) reflection coefficients in the frequency range of 92-110 GHz. A stochastic model for single reflection fixed links that is capable of modelling random scattering from small-scale discontinuities such as those encountered in complex structures in walls and partitions of buildings is presented. The model auto-regressively produces filter coefficients that are fed into an Infinite-Impulse-Response (IIR) filter which convolves them with the spatio-temporal series in order to generate the next output sample based on previous observations. The IIR filter allows for flexible stochastic generation of samples, and its parameters can be adjusted as needed to suit different channel conditions. A total of 20 suitable start-up filter coefficients are generated from 21.7 % of the sample size for each complex delay tap distribution, which corresponds to 50 complex instances of the channel. These coefficients are then utilised to validate the remaining measured sample set. The model is in quantitative agreement with measurement statistics and can be used to construct relatively simple modified reflection coefficients that can be used in micro-cellular ray-optical network planning tools.

Although Geostationary-Equatorial-Orbit (GEO) satellites have achieved significant success in conducting space missions, they cannot meet the 5G latency requirements due to the far distance from the earth surface. Therefore, Low-Earth-Orbit (LEO) satellites arise as a potential solution for the latency problem. Nevertheless, integrating the 5G terrestrial networks with LEO satellites puts an increased burden on the satellites' limited budget, which stems from their miniature sizes, restricted weights, and the small available surface for solar harvesting in the presence of additional required equipment. This paper aims to design the Electrical Power System (EPS) for 5G LEO satellites and investigate altitudes that meet the latency and capacity requirements of 5G applications. In this regard, accurate solar irradiance determination for the nadir-orientation scenario, Multi-Junction (MJ) solar cells modeling, backup batteries type and number, and designing highly-efficient converters are addressed. Accordingly, the power budgeting of the 5G LEO satellite can be achieved based on defining the maximum generated power and determining the satellite's subsystem power requirements for 5G missions. In the sequel, the measured and simulated values of the electrical V-I characteristics of an MJ solar panel are compared to validate the model by using a Clyde Space solar panel that reaches a maximum power generation of approximately 1~W at ( I_{MPP}=0.426\,\,A , V_{MPP}=2.35\,\,V ). Moreover, a synchronous boost converter circuit is designed based on commercial off-the-shelf elements.

The abundant spectrum resources and low beam divergence of the terahertz (THz) band can be combined with the orthogonal propagation property of orbital angular momentum (OAM) beams to multi-fold the capacity of wireless communication systems. Here, a reflective metasurface (RMTS) is utilized to enhance the coverage of the high gain THz OAM beams by enabling the non-line-of-sight (NLoS) component by reshaping the planar wavefront of the incident wave into the helical wavefront, so that it is redirected towards the direction of interest. This can contribute to alleviating the concern of the small aperture size, since improving the channel capacity can be achieved at the low spectrum blocks of the THz band (larger aperture size). For validation, three 90 × 90 mm RMTSs are simulated, fabricated, and tested in the frequency range 90-110 GHz, to re-direct single and dual OAM beams towards the desired location.

This paper proposes a novel method to enable mode and polarization OAM multiplexing at four different frequencies (30, 70, 90, and 110 GHz) through a reflectarray (RA) antenna. The suggested RA delivers almost matched electromagnetic (EM) responses for x- and y-polarized incident waves for both reflected OAM modes of l=2 . The designed antenna can considerably improve channel capacity and spectrum efficiency.

The power consumption of reconfigurable intelligent surfaces (RIS) has not been addressed enough in the state-of-theart. This paper proposes a paradigm for converting RISs into ecofriendly structures that generate their needed power by the highefficiency multiple junctions (MJ) solar cells. This work considers the impact of adding solar cells to the RIS and investigates the amount of generated power. Moreover, the inclination angle of the solar irradiance is considered as well as the needed batteries and converters. Since the introduced RIS can be a potential candidate for the 5G-and-beyond-communications, two ranges of frequencies will be discussed in this work: sub-6GHz and 5G Millimeter wave (mmWave).

The power consumption of reconfigurable intelligent surfaces (RIS) has not been addressed enough in the state-of-the-art. This paper proposes a paradigm for converting RISs into eco-friendly structures that generate their needed power by the high-efficiency multiple junctions (MJ) solar cells. This work considers the impact of adding solar cells to the RIS and investigates the amount of generated power. Moreover, the inclination angle of the solar irradiance is considered as well as the needed batteries and DC-DC converters. Since the introduced RIS can be a potential candidate for the 5G-and-beyond-communications, two ranges of frequencies will be discussed in this work: sub-6GHz and 5G Millimeter wave (mmWave).

A circular reflectarray antenna (RA) for generating Orbital Angular Momentum (OAM) modes in the Terahertz (THz) band is introduced. An interlaced unit cell is proposed to reach a phase variation of 328 at 185 GHz to 188 GHz. Combining RA, OAM, and THz technologies in one structure can be utilized to reach the future requirements of 6G networks. That is due to the additional degree of freedom that OAM beams can provide for data multiplexing in short-distance wireless communication.

—This paper introduces the latest designed electromagnetic metasurfaces at the Institute for Communication Systems (ICS) for 5G-and-beyond networks. Various technologies and metasurfaces at different frequency ranges were developed to solve the drawbacks related to metasurfaces such as the limited bandwidth and Non-line-of-sight (NLoS) coverage issues. I. REFLECTIVE METASURFACES FOR 5G AND 6G COMMUNICATIONS One core objective of applying reflective metasurfaces in future communication systems is to provide electromagnetic (EM) coverage in the network's blind spots [1]. This happens by regulating the aperture response when it is illuminated by EM source(s), to purposefully reflect the incoming waves to the direction of interest. Controlling the aperture response can be done by the generalized Snell's law of reflection and holographic technique. In this section, we introduce two reflective metasurfaces based on these two techniques. A. Reconfigurable Intelligent Surface based on Generalized Snell's Law of Reflection A reconfigurable intelligent surface (RIS) is presented in [2] where the generalized Snell's law of reflection is applied to regulate the phase profile on the surface. This method requires knowledge about the location of the EM source and the direction of reflection, as well as the spacing between the unit cells on the surface. In a designed structure, the unit cell spacing (periodicity) is in general constant, but the location of the EM source and the direction of reflection can vary case by case. Hence, it is required to add a controllable component (varactor diode in [2]) to the physics of the unit cell to correspondingly customize the response of the surface and to make a reconfigurable structure. B. Reflective Metasurface based on Holography Technique A holographic-based reflective metasurface is presented in [3]. In the holography technique, the direction of the incoming waves must be known, and then, based on the direction of reflection, an interferogram will be obtained which is the so-called EM hologram. With this technique, it is possible to define more than one reflected beam, resulting in multi-spot coverage provisioning. Under this circumstance, the su-perposition of the desired reflecting beams will contribute to calculating the EM hologram. A dual-beam reflector is designed in [3] correspondingly. II. REFLECTIVE METASURFACE FOR OAM BEAMS GENERATION Orbital angular momentum (OAM) beams have been suggested as a strong solution to increase the channel capacity of a communication system by utilizing many orthogonal independent channels without using extra frequency resources [4]. Therefore, they can be used to solve the limited bandwidth drawback of metasurfaces. A. Reflective Metasurface with Steered OAM Beams Three environment-friendly reflective metasurfaces with single and dual-directed OAM beams to tackle the poor network coverage of THz waves in the absence of LoS communications are introduced in [5]. The integration between the OAM and THz RMTS technologies can improve spectral efficiency through a low-cost and low-profile solution. The presented metasurfaces of 90 × 90 mm were simulated, fabricated, and tested to verify the capability to control and steer the wavefront of the EM waves in the frequency range 90-110 GHz. B. THz reflectarray antenna with OAM multiplexing and beam-steering capabilities The unexplored potentials of reflectarray antennas to manipulate OAM beams are examined at 330 GHz in [6]. It investigated the maximum achievable angles by a planar meta-surface per single feed for a single OAM beam. That motivated the proposed work to investigate the possibility of generating multiple off-centered OAM beams of different modes with the maximal achievable angles for OAM multiplexing and beam-scanning applications through passive structures. The designed RAs can be envisaged for THz indoor communications. III. REPROGRAMMABLE GRAPHENE-BASED DIGITAL METASURFACE The metasurfaces using phase-only or amplitude-only engineering have limited the full functionality of the devices. In [7], a digital graphene-based metasurface simultaneously manipulating both amplitude and phase has been proposed to address this challenge in the terahertz (THz) band. As Fig. 1(c) presents conceptually, leveraging a 2/2-bit digital unit cell with independent control of 2-bit states of amplitude and phase, an efficient multi-focal meta-lens has been demonstrated. Moreover , the proposed metasurface has been applied to develop a

In this paper, we investigate the reflection properties of different interior surfaces in the 92-110 GHz sub-Terahertz (THz) band. The measurements were conducted in an indoor environment by placing the surface in a specular configuration between the Transmitter (Tx) and Receiver (Rx) and collecting a large set of data by offsetting the Tx and Rx in parallel to the surface. The measurements were performed using an Agilent N5230A Vector-Network-Analyzer (VNA). In particular, we present a statistical analysis in the frequency domain to show how frequency selective each surface reflection is and how constant this behaviour is across the whole data set. We introduce the Power-Delay-Profile (PDP) to characterize the multipath behaviour of the channel and calculate the Root-Mean-Square (RMS) delay spread. The measurement results provide a good insight for future propagation work to be done for the development of indoor communications systems at sub-THz frequencies.

This paper presents a method to generate multiple spot beam coverage based on metasurfaces where the incident wavefront from a single feeder is manipulated to reflect multiple off-centred beams. The proposed method produces four steered beams to secure continuous connection for different gateways (GWs) at an operation frequency of 35 GHz. A sub-wavelength unit cell (\lambda/8) is adopted to reduce the phase quantization error and to have smooth phase distribution over the aperture.

A circular reflectarray antenna (RA) for generating Orbital Angular Momentum (OAM) modes in the Terahertz (THz) band is introduced. An interlaced unit cell is proposed to reach a phase variation of \boldsymbol {328^{\mathrm{\circ}}} at 185 GHz to 188 GHz. Combining RA, OAM, and THz technologies in one structure can be utilized to reach the future requirements of 6G networks. That is due to the additional degree of freedom that OAM beams can provide for data multiplexing in short-distance wireless communication.

—The proposed intelligent reflective surface (IRS) is presented to compensate for the path loss and enhance the coverage of 5G networks at mm-wave band. A (π) shaped element with variable-sized dipoles, distributed in a certain way to maintain a phase length curve over 340 • in the range of 23-27 GHz, is addressed in this work. The proposed structure can be an ideal candidate for 5G mm-wave band n258.

The proposed structure is presented to improve the inherited limited bandwidth and reduce the production of grating lobes in reflectarray antennas (RAs). A dielectric RA with 200 mm × 200 mm is designed and simulated to produce an orbital angular momentum beam (OAM) of the second mode with averaged realized gain of around 20 dBi in the band of 25-40 GHz, which covers most of 5G mm-wave bands (n257, n258, n260, and n261). To achieve the mentioned specifications, an inter-element spacing of 0.25λ is adopted.

This letter presents experimental angularly resolved measurements and a model framework for characterizing continuous wideband reflection coefficients at sub-terahertz frequencies between 92 and 110 GHz. Surfaces that appear "smooth" but with internal features comparable to the wavelength have shown to cause frequency selective scattering. An nth-degree polynomial regression model is employed to quantify non-linear multi-path scattering that cannot be described by a best-fit line, with least-squares regression applied to find the best-fitting polynomial and hence the coefficients. The obtained coefficients are then validated against the delay domain statistics of the propagation channel, demonstrating the proposed model's good agreement with measurements and its efficiency in reproducing angle-dependent reflection coefficients for use in ray-tracing tools. This letter presents experimental angularly resolved measurements and a model framework for characterizing continuous wideband reflection coefficients at sub-terahertz frequencies between 92 and 110 GHz. Surfaces that appear "smooth" but with internal features comparable to the wavelength have shown to cause frequency selective scattering. An nth-degree polynomial regression model is employed to quantify non-linear multi-path scattering that cannot be described by a best-fit line, with least-squares regression applied to find the best- fitting polynomial and hence the coefficients. image

Substrate integrated waveguides (SIW) technology is employed to design a uniform long slot leaky-wave antenna (LWA) in millimeter-wave (mmWave) band. The structure is then loaded by a 3D printed sinusoidal periodic pattern of Photopolymer VeroClear dielectric. This makes a periodic LWA which means that it is possible to regulate a desired higher order space harmonic to form the beam and to tilt it to the direction of interest. To showcase the practicality of method, the dielectric pattern is designed in such a way that the beam is tilted to the backward-quadrant at θm = −15 • at f = 35 GHz. The structure is fabricated and the S-parameters are measured which shows a good agreement with the simulated results. Index Terms—leaky wave antenna (LWA), 3D printing, sub-strate integrated waveguide (SIW), periodic structure.

In conventional hybrid beamforming approaches, the number of radio-frequency (RF) chains is the bottleneck on the achievable spatial multiplexing gain. Recent studies have overcome this limitation by increasing the update-rate of the RF beamformer. This paper presents a framework to design and evaluate such approaches, which we refer to as agile RF beamforming, from theoretical and practical points of view. In this context, we consider the impact of the number of RF-chains, phase shifters speed, and resolution to design agile RF beamformers. Our analysis and simulations indicate that even an RF-chain-free transmitter, which its beamformer has no RF-chains, can provide a promising performance compared with fully-digital systems and significantly outperform the conventional hybrid beamformers. Then, we show that the phase shifter's limited switching speed can result in signal aliasing, in-band distortion, and out-of-band emissions. We introduce performance metrics and approaches to measure such effects and compare the performance of the proposed agile beamformers using the Gram-Schmidt orthogonalization process. Although this paper aims to present a generic framework for deploying agile RF beamformers, it also presents extensive performance evaluations in communication systems in terms of adjacent channel leakage ratio, sum-rate, power efficiency, error vector magnitude, and bit-error rates.

In this paper, an 8×8 Multiple Input Multiple Output (MIMO) antenna design for Fifth Generation (5G) sub- 6GHz smartphone applications is presented. The antenna elements are based off a folded quarter wavelength monopole that operate at 3.4-3.8GHz. Isolation between antenna elements is provided through physical distancing. The fabricated antenna prototype outer casing is made from Rogers R04003C with dimensions based on future 5G enabled phones. Measured results show an operating bandwidth of 3.32 to 3.925GHz (S11 < 6dB) with a transmission coefficient < -14.7dB. A high total efficiency for an antenna array is also obtained at 70-85.6%. The design is suitable for MIMO communications exhibited by an Envelope Correlation Coefficient (ECC) < 0.014. To conclude a Specific Absorption Rate (SAR) model has been constructed and presented showing the user’s effects on the antenna’s Sparameter results. Measurements of the amount of power absorbed by the head and hand during operation have also been simulated.

© 2009-2012 IEEE.A system involving W-band (75-110 GHz) optical millimeter (mm)-wave generation using the external optical modulator (EOM) in a radio-over-fiber (RoF) link is presented for satisfying the requirements for multi-gigabit-per-second data rates. A 90-GHz mm-wave signal was generated by a nonupling (nine times) increase in only a 10-GHz local oscillator by biasing the EOM at its zero level and choosing an appropriate modulation index. To achieve a fast transmission speed wirelessly, high spectral efficiency (SE), and better transmission performance, orthogonal frequency-division multiplexing (OFDM) is used. The bit error rate (BER) and error vector magnitude (EVM) of the system were measured for three different fiber lengths and for a wireless distance of 1-5 m. The results show that the system with the SE of ∼4 (b/s)/Hz and 16-ary quadrature amplitude modulation (QAM) 40-GB/s OFDM signals can be received by the end user with BER less than 3.8 × 10-3 and EVM less than 25% over a 50-km optical fiber and 3-m wireless link.

In this paper, an ultra-wideband, Dielectric Resonator Antenna (DRA) has been proposed. The proposed antenna is based on isosceles triangular DRA (TDRA), which is fed from the base side using a 50Ω probe. For bandwidth enhancement and radiation characteristics improvement, a partially cylindrical-shape hole is etched from its base side which approached probe feed to the center of TDRA. The dielectric resonator (DR) is located over an extended conducting ground plane. This technique has significantly enhanced antennas bandwidth from 48.8% to 80% (5.29-12.35 GHz), while the biggest problem was radiation characteristics. The basis antenna possesses negative gain in a wide range of bandwidth from 7.5 GHz to 10.5 GHz down to -13.8 dBi. Using this technique improve antenna gain over 1.6 dBi for whole bandwidth, while peak gain is 7.2 dBi.

Utilizing the holography theory, a bidirectional wideband leaky wave antenna in the millimetre wave (mmW) band is presented. The antenna includes a printed pattern of continuous metallic strips on an Alumina 99:5% sheet, and a surface wave launcher (SWL) to produce the initial reference waves on the substrate. To achieve a bidirectional radiation pattern, the fundamental TE mode is excited by applying a Vivaldi antenna (as the SWL). The proposed holographic-based leaky wave antenna (HLWA) is fabricated and tested and the measured results are aligned with the simulated ones. The antenna has 22:6% fractional bandwidth with respect to the central frequency of 30 GHz. The interference pattern is designed to generate a 15 deg backward tilted bidirectional radiation pattern with respect to the normal of the hologram sheet. The frequency scanning property of the designed HLWA is also investigated.

A high-resolution conformal array for detection of small size tumors inside the breast is proposed. The array consists of a novel cavity-backed low-profile aperture-stacked-patch (LP-ASP) antennas. The proposed antenna operates from 2.2 GHz to 13.5 GHz which enables the imaging system to be exploited across a high fractional bandwidth of approximately 149%. Thanks to the wide operating bandwidth of the designed antenna, the proposed system is not only applicable for a deep penetration imaging, but also for high resolution and accurate images acquisition. The proposed single element antenna has a compact size of \mathrm {10 \times 10 \times 10.495 m}\mathrm {m}^{3} . So, it is possible to form a conformal array around the breast by applying numbers of the designed elements. Moreover, a Hybrid Artifact Suppression (HAS) method is presented to remove the artifact effects including skin reflection and mutual coupling between the elements. In this method, the artifact response of each channel is estimated using Independent Component Analysis (ICA) at the early-stage of the recorded signals. Additionally, in order to suppress the artifact data to accurately detect the malignant tumor, a Wiener filter is applied. To validate the practicality of the presented calibration algorithm in the proposed conformal array, the detection of a single spherical tumor (with a small diameter of 5 mm) within a realistic breast model in different scenarios is studied. Investigating of simulated and measured results of the designed antenna, and comparing quantitative metrics of successfully reconstructed tumor images by the proposed HAS and conventional calibration methods show the proposed system can be a good candidate for the breast cancer detection applications.

This article presents a unique technique to enhance isolation between transmit/receive radiating elements in densely packed array antenna by embedding a metamaterial (MTM) electromagnetic bandgap (EMBG) structure in the space between the radiating elements to suppress surface currents that would otherwise contribute towards mutual coupling between the array elements. The proposed MTM-EMBG structure is a cross-shaped microstrip transmission line on which are imprinted two outward facing E-shaped slits. Unlike other MTM structures there is no short-circuit grounding using via-holes. With this approach, the maximum measured mutual coupling achieved is -60 dB @ 9.18 GHz between the transmit patches (#1 & #2) and receive patches (#3 & #4) in a four-element array antenna. Across the antenna’s measured operating frequency range of 9.12 to 9.96 GHz, the minimum measured isolation between each element of the array is 34.2 dB @ 9.48 GHz, and there is no degradation in radiation patterns. The average measured isolation over this frequency range is 47 dB. The results presented confirm the proposed technique is suitable in applications such as synthetic aperture radar (SAR) and multiple-input multiple-output (MIMO) systems.

This communication proposes a compact, low-profile patch antenna with omni-directional radiation pattern and vertical polarization. A pair of shorted patches are excited in-phase to achieve the omni-directivity and the vertical polarization, simultaneously. The principle is to excite two back-to-back arranged shorted patches to generate symmetrical electric field (E-field) distributions normal to the ground plane. Analytical study on how to generate the omni-directional radiation pattern is carried out. Base on this study, we found the spacing in-between the two patches have little influence on the radiation characteristics, which provides another flexibility in the design. In addition, the shape of the patch and the corresponding field distribution are investigated to further improve the omni-directivity. To improve the impedance bandwidth, resonant structures are inserted in-between the patches, producing the 2nd order response in frequency. The antenna has been fabricated and characterized, and the measured results are in a reasonable agreement with the simulations, showing that the proposed antenna is suitable for potential surface-mount wireless applications.

A new simple and accurate model defined as shield edge diffraction is derived and validated suitable for frequencies above 10GHz diffracting around obstructions that are narrow compared to the Fresnel zone width. The model includes new simple Fresnel diffraction parameters similar to those used with traditional knife edge diffraction, which can in the same way be integrated into deterministic and empirical path loss models. Capability of the model extends beyond current single and double knife edge models whereby it includes the effects of the antennas’ far field distances as well as their gain and phase patterns, which subsequently have a severe effect on the diffraction loss in short range links. The models are validated using both anechoic chamber as well as real environment based measurements at 10-12GHz and 26GHz.

In this paper, empty substrate integrated waveguides (ESIW) technology is applied to design long slot leaky-wave antennas (LWAs). First, a uniform-aperture structure is presented and its limitations on forming the beam are studied. Then, a sinusoidal curve is employed to modify the geometry of guided-wave structure which divides the slot into a number of segments, making a periodic aperture. After that, a method is proposed to regulate the guided waves inside the ESIW. To this end, a modulation function is derived to simultaneously determine the local amplitude and segment length of the physical sinusoidal curve at each individual points on the structure. This results in manipulating the phase constant (_) and leakage rate (_) across the aperture which ultimately controls both the tilt angle and side-lobe-level (SLL) of the constructed beam. The slot is placed on the centerline of the broad wall of the ESIW in order to reduce the cross polarization. The structure is designed to operate at 35 GHz with SLL = 􀀀30 dB and a backward tilt angle of _m = 􀀀20 deg. Finally, the proposed LWA is simulated and a fabricated design is measured. A good agreement is observed between the theoretical, simulated, and measured performance of the antenna.

In this paper, a Rectangular Dielectric Resonator Antenna (RDRA) with a modified feeding line is designed and investigated at 28 GHz. The modified feed line is designed to excite the DR with relative permittivity of 10 which contributes to a wide bandwidth operation. The proposed single RDRA has been fabricated and mounted on a RT/Duroid 5880 (εr = 2.2 and tanδ = 0.0009) substrate. The optimized single element has been applied to array structure to improve the gain and achieve the required gain performance. The radiation pattern, impedance bandwidth and gain are simulated and measured accordingly. The number of elements and element spacing are studied for an optimum performance. The proposed antenna obtains a reflection coefficient response from 27.0 GHz to 29.1 GHz which cover the desired frequency band. This makes the proposed antenna achieve 2.1 GHz impedance bandwidth and gain of 12.1 dB. Thus, it has potential for millimeter wave and 5G applications.

A reconfigurable metamaterial-inspired unit cell is proposed that can be reconfigured to behave either as a perfect magnetic conductor (PMC) or as a perfect electric conductor (PEC) and its application to waveguide miniaturisation is demonstrated. The unit cell is designed to operate in the sub-6 GHz band at 3.6 GHz with a PMC bandwidth of ≈ 150 MHz and has a simple construction that makes the design easy to fabricate. The phase response of the reconfigurable unit cell is presented and a prototype design of a miniaturised waveguide using the proposed unit cell is also proposed. The performance and field distribution of the waveguide are analysed which demonstrate the existence of a pass-band spanning ≈ 160 MHz below the cutoff frequency and the presence of a quasi TEM mode.

In this paper the A-shape dielectric resonator antenna is modified for circular polarization in low frequencies of wireless applications. In order to have a wide bandwidth, a dielectric with low permittivity is employed. Another dielectric resonator owning a high permittivity is stacked to the other one, which is assigned to provide circular polarization. A Pshape parasitic strip is embedded between the two resonators to guide electrical and magnetic fields for a low axial ratio (AR) over a wide bandwidth. The proposed DRA with good radiation characteristics offers a bandwidth of 34% between 2.90 GHz and 4.11 GHz and an axial ratio of 18%between 3.40 GHz and 4.04GHz for the first band and a bandwidth of 18% between 5.16 GHz and 6.16 GHz for the second band that all support 2.4 GHz Bluetooth, WLAN, 3.3-3.6 GHz (WiMax), 3.8-4.1 GHz (C-band), 4.8-6.2 GHz (5.2, 5.5 & 5.8 GHz-WLAN & WiMax) © 2011 IEEE.

Millimeter wave (mmWave) systems with effective beamforming capability play a key role in fulfilling the high data-rate demands of current and future wireless technologies. Hybrid analog-todigital beamformers have been identified as a cost-effective and energy-efficient solution towards deploying such systems. Most of the existing hybrid beamforming architectures rely on a subconnected phase shifter network with a large number of antennas. Such approaches, however, cannot fully exploit the advantages of large arrays. On the other hand, the current fully-connected beamformers accommodate only a small number of antennas, which substantially limits their beamforming capabilities. In this paper, we present a mmWave hybrid beamformer testbed with a fully-connected network of phase shifters and adjustable attenuators and a large number of antenna elements. To our knowledge, this is the first platform that connects two RF inputs from the baseband to a 16 8 antenna array, and it operates at 26 GHz with a 2 GHz bandwidth. It provides a wide scanning range of 60, and the flexibility to control both the phase and the amplitude of the signals between each of the RF chains and antennas. This beamforming platform can be used in both short and long-range communications with linear equivalent isotropically radiated power (EIRP) variation between 10 dBm and 60 dBm. In this paper, we present the design, calibration procedures and evaluations of such a complex system as well as discussions on the critical factors to consider for their practical implementation.

This paper presents a fully-transparent and novel frequency selective surface (FSS) that can be deployed instead of conventional glass to reduce the penetration loss encountered by millimeter wave (mmWave) frequencies in typical outdoorindoor (O2I) communication scenarios. The presented design uses a 0:035 mm thick layer of indium tin oxide (ITO), which is a transparent conducting oxide (TCO) deposited on the surface of the glass, thereby ensuring the transparency of the structure. The paper also presents a novel unit cell that has been used to design the hexagonal lattice of the FSS structure. The dispersion and transmission characteristics of the proposed design are presented and compared with conventional glass. The presented FSS can be used for both 26 GHz and 28 GHz bands of the mmWave spectrum and offers a lower transmission loss as compared to conventional glass without any considerable impact on the aesthetics of the building infrastructure.

A novel high-isolation dual-polarized in-band full-duplex (IBFD) dielectric resonator antenna (DRA) for satellite communications using a decoupling structure is proposed. Good isolation between transmit and receive ports is achieved by placing two identical linearly polarized resonators orthogonal to each other. Each resonator consists of a main rectangular dielectric resonator of the dielectric constant of 10 and is loaded by a thin dielectric slab of lower permittivity of 5 to broaden the matching bandwidth further. The isolation is further improved by loading an absorber and etching several slots in the ground plane. Finally, the proposed DRA is fabricated and measured to validate the concepts. Measurement results show high isolation of more than 50 dB over the desired operating bandwidth from 23.04 GHz to 24.08 GHz (ka-band) with a peak gain of about 8.93 dBi and 8.09 dBi for Port 1 and Port 2, respectively. In addition, the proposed IBFD DRA provides 11.87 GHz and 4.84 GHz isolation bandwidths over 25 dB and 30 dB, respectively, making it a potential candidate for mm-wave terrestrial applications.

This paper presents empirically-based large-scale propagation path loss models for small cell fifth generation (5G) cellular system in the millimeter-wave bands, based on practical propagation channel measurements at 26 GHz, 32 GHz, and 39 GHz. To characterize path loss at these frequency bands for 5G small cell scenarios, extensive wideband and directional channel measurements have been performed on the campus of the University of Surrey. Close-in reference (CI), and 3GPP path loss models have been studied, and large-scale fading characteristics have been obtained and presented.

© 2015 EurAAP.A four-port MIMO dielectric resonator antenna (DRA) is studied and proposed. The antenna consisting of four rectangular dielectric resonator (RDR) elements, each one is fed by a coplanar feed line, is fabricated on FR4 substrate. A parametric study is carried out and the presented antenna has been fabricated. The presented MIMO DRA having good MIMO characteristics offers a measured bandwidth of 250 MHz between 2480 MHz and 2730MHz for S11 < -10dB, which can operate on LTE bands 7 (2500-2570MHz) and 38 (2570-2620MHz). In these frequency bands the measured isolation is less than -17dB. By calculating and measuring the envelop correlation coefficient, mean effective gains and the diversity gain, the MIMO performance of the presented antenna has been examined. The antenna presented is easy to feed, fabricate, and can be a good candidate for LTE femtocell access point applications.

© 2015, Penerbit UTM Press. All rights reserved.This paper presents the design of a beam steerable array antenna based on branch line coupler (BLC) at 28 GHz frequency band for fifth generation (5G) wireless applications. The array is designed using Rogers RT/duroid 5880 substrate material of 0.254 mm thickness and dielectric constant of 2.2. The designed antenna has six elements array and is fed by a BLC which serves as a beamformer to obtain the beam scanning ranging from -16 to +16 degrees. The maximum gain of 14.5 dBi and a wideband that cover from 25.2 GHz to 32 GHz was obtained by measurement. The proposed antenna is applicable to 28 GHz frequency band proposed for 5G wireless communications. All simulated and measured results are clearly presented.

© 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:495-501, 2015. © 2014 Wiley Periodicals, Inc.A dual-port reduced size multiple input multiple output (MIMO) Dielectric Resonator Antenna (DRA) has been studied and proposed. The MIMO antenna consists of a Rectangular Dielectric Resonator antenna, which is fed by two symmetrical feed lines for orthogonal mode excitation. The proposed antenna is suitable for operation over various long term evolution (LTE) bands. A measured bandwidth of 264 MHz for |S11|

Conference Title: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/USNC-URSI) Conference Start Date: 2022, July 10 Conference End Date: 2022, July 15 Conference Location: Denver, CO, USAA dual-polarized dielectric resonator antenna (DRA) is investigated and discussed. The probe and microstrip feed line excite linear polarization (LP) and broadside circular polarization (CP), respectively. These different radiation patterns are obtained 43 % overlapping bandwidth. The measured results show that the antenna provides 43 % bandwidth, excited by probe feed line that produces linearly polarized and 74 % impedance bandwidth using microstrip feed line with the 18 % circularly polarized. The total overlapping bandwidth is 43 % starting from 8.65 GHz to 13.44 GHz. The antenna gain is between 3.4 and 5.2 dBi for linear polarized and between 2.8 and 5.1 dBi for circularly polarized patterns in the whole covered range.

A wideband circularly polarized (CP) rectangular dielectric resonator (DR) parasitically coupled to a printed rectangular loops is presented. The DR is housed in a thin dielectric substrate with a microstrip line and narrow strip printed from one side and a ground plane and conducting loops and lines connected to the ground plane. The DR is linearly polarized, and for CP, we introduced printed conducting loops in the other side of the DR, which produce the orthogonal polarization with the required quadratic phase. Several loops are used to achieve the wide CP band. The final design achieves CP with 51% bandwidth. The reflection coefficient, axial ratio (AR), radiation patterns, gain, and efficiency of the antenna are studied, and reasonable agreement between the measured and simulated results is observed. © 2011 IEEE.

A mobile ad hoc network (MANET) poses significant challenges such as route failure and end-to-end delay due to the decentralized nature of mobile ad hoc wireless networks, mobility of devices, and resource constraints. Motivated by this, in this work, a new routing protocol by implementing intelligent reflecting surfaces (IRSs) in MANET, called MRIRS, is proposed. The developed MRIRS investigates the role of IRS as an intermediate node which helps not only for multi-flow multi-path routing even in non-line-of-sight (NLoS) scenarios but also supports delay minimization in the route discovery phase and helps with interference-avoiding channel assignment to the primary users (PUs). Comparison in terms of packet delivery ratio (PDR) and end-to-end delay (PD) averaged on 40 topologies based on the same source and destination pair with 3 flows shows that MRIRS has an 8% improvement in PDR and 800 msec improvement in PD. In environments with 8 m/s average node speed, MRIRS shows 114.88 kbps improvement in terms of throughput where 15.97% link failure is recorded on average. In environments with 16 m/s, link failure is around 24% where it is almost 98% for other routing protocols.

This paper presents the design of a Ka-band reflectarray antenna, intended for LEO-satellite communications, which operates at 27 GHz. The phase tuning mechanism relies on variable size patches capable of achieving a 360 degrees phase range, which enables the incoming wave to be scattered in any specific direction. In particular, the reflectarray antenna, which has a squared-shape of 30 cm each side, is constituted by a 50 x 50 radiating-patch elements, printed on a planar substrate of "Rogers TMM4" material. With a 27.41 dBi directivity, this configuration is able to generate a pencil-beam in perpendicular direction to the reflecting plane.

The Terahertz (THz) band (0.3-3.0 THz), spans a great portion of the Radio Frequency (RF) spectrum that is mostly unoccupied and unregulated. It is a potential candidate for application in Sixth-Generation (6G) wireless networks, as it has the capabilities of satisfying the high data rate and capacity requirements of future wireless communication systems. Profound knowledge of the propagation channel is crucial in communication systems design, which nonetheless is still at its infancy, as channel modeling at THz frequencies has been mostly limited to characterizing fixed Point-to-Point (PtP) scenarios up to 300 GHz. Provided the technology matures enough and models adapt to the distinctive characteristics of the THz wave, future wireless communication systems will enable a plethora of new use cases and applications to be realized, in addition to delivering higher spectral efficiencies that would ultimately enhance the Quality-of-Service (QoS) to the end user. In this paper, we provide an insight into THz channel propagation characteristics, measurement capabilities, and modeling techniques for 6G communication applications, along with guidelines and recommendations that will aid future characterization efforts in the THz band. We survey the most recent and important measurement campaigns and modeling efforts found in literature, based on the use cases and system requirements identified. Finally, we discuss the challenges and limitations of measurement and modeling at such high frequencies and contemplate the future research outlook toward realizing the 6G vision.

A multifunctional antenna with diverse radiation patterns in different frequency bands (2.45/5.8 GHz) is presented in this paper. The antenna has a low profile but exhibits an omni-directional radiation pattern in the low-band operation and uni-directional pattern in the high-band operation. For the high-band operation, a 2 × 2 patch arrays are designed by employing a out-of-phase feeding method. The low-band operation with the omni-directional pattern is achieved by exciting four open-ended slots in-phase. The four slots are slit in the ground of the high-band array and in this way, this footprint of the antenna is maintained. The operating principles of the antenna are studied with the aid of equivalent circuit model and the current distribution. The antenna is prototyped and measured, demonstrating good results in terms of bandwidths, inter-channel isolation, radiation characteristics.

This study examines the effect of different pressures on the radiation characteristics of the loop-shaped plasma antenna filled by two gases; Argon and Nitrogen. Proposed loop plasma antennas operating at LTE and Wi-Fi frequency bands have been designed and its performance studied at three different pressures of 2.28, 5 and 10 Torr. The radiation characteristics of the both loop-shaped plasma antennas have been investigated and presented for three different pressures. To analyze the performance of the proposed antenna, full-wave simulation were run using the finite integral method software, CST Microwave Studio.

The design, simulation and fabrication of a P-shaped monopole antenna for wireless body area networks (WBAN) applications is presented in this paper. It is noted that the radiation characteristics was improved by attaching a P-shaped element to the ground plane. The simulation of the proposed antenna in the free space and close proximity of body surface has been done using CST Microwave Studio. The proposed antenna is designed on the FR4 substrate with dielectric constant of 4.4 and 1.6mm thickness; and the operating frequency band is between 3.1 to 5.1GHz. The final optimized design has dimensions of 32mm ×28mm. The proposed antenna improves the gain of close proximity of body surface. In addition, the antenna improves the reflection coefficient when placed close human body compared to other antennas. It was observed that there is good agreement between the simulation and measurement results, thereby showing that the antenna is potential to be deployed for WBAN application. © 2014 SERSC.

A new design of a circularly-polarized (CP) trapezoidal dielectric resonator antenna (DRA) for wideband wireless application is presented. A single-layered feed is used to excite the trapezoidal shaped dielectric resonator to increase resonant frequency and axial ratio. Besides its structure simplicity, ease of fabrication and low-cost, the proposed antenna features good measured impedance bandwidth, 87.3% at 4.21GHz to 10.72 GHz frequency bands. Moreover, the antenna also produces 3-dB axial ratio bandwidth of about 850 MHz from 5.13 GHz to 6 GHz. The overall size of DRA is 21 mm × 35 mm, which is suitable for mobile devices. Parametric study and measurement results are presented and discussed. Very good agreement is demonstrated between simulated and measured results.

We present the concept of holographic beam forming metasurface antenna for CubeSat platforms at X-band frequencies. The proposed metasurface topology exhibits a flat-panel system layout, particularly desirable for integration with CubeSat platforms without a hardware-intense deployment mechanism for launch. It is shown that appropriately interacting the guidedmode (or reference-wave) with a metasurface layer makes it possible to realize the radiation pattern of interest as an objective function - similar to an optical hologram - without the need for dedicated phase shifting circuits. The full-wave simulations of the designed metasurface layer integrated with a 1U CubeSat reveals a high-fidelity beam-control with an aperture efficiency greater than 40% at 10 GHz operating frequency.

In this paper, a dual-polarized reconfigurable metacavity transceiver (DRMT) that can be applied in computational polarimetric imaging (CPI) is proposed. The transmitter and the receiver of a CPI system are replaced by two ports of the DRMT, which significantly simplifies the hardware architecture. The DRMT is an electrically over-sized metacavity with its back wall replaced by a reconfigurable metasurface (i.e., PIN diode loaded metasurface) and its top surface etched with leaky cross-shaped irises. By altering the PIN state of each metamaterial element, spatially orthogonal measurement modes can be obtained. Furthermore, due to the polarizationindependence of the cross-shaped iris, measurement modes under different polarization states are also orthogonal to each other. In addition, the proposed DRMT exhibits a broadband operational characteristic, facilitating its application in different scenarios. The reflection coefficients under different PIN states are under -10 dB, indicating that the two ports of the DRMT are impedancematched. The mutual coupling coefficients are under -30 dB, demonstrating good isolation between the ports. The correlation coefficients are smaller than 0.2 and the singular values are close to each other, which proves the spatial-orthogonality of the measurement modes. The DRMT-based full-wave CPI simulations are also implemented and polarimetric images were reconstructed using different polarization components to showcase the benefits of the CPI method.

—In this paper an all metallic band pass filter with high power handling capability is proposed. The operating frequency bandwidth of the design can be determined by tuning the proposed modulation parameters of the ridge in the waveguide. As a proof of concept, a bandwidth from 11GHz up to 29GHz is selected to force the waveguide to operate in single mode scenario to mitigate multi mode dispersion by simply adding a transition from ridge waveguide to a normal one.

Sixth-generation cellular networks (6G) are expected to involve not only data communications but also sensing capabilities, enabling a wide range of applications. This paper proposes a novel Dual Functional Shared Aperture reconfigurable intelligent surface (RIS) design that enables the coexistence between radar sensing and millimeter wave (mm-wave) communication. Some RIS meta-elements integrate radio-frequency (RF)-feeds to support the transmission/reception of multiple-input multiple-output (MIMO) radar signals, permitting holographic beam focusing/forming in near/far fields without phase shifters. The designed Dual Functional RIS provides a synergy between communication and sensing modalities, particularly in scenarios where both far-field and near-field interactions play critical roles. Primarily, we emphasize far-field conditions and antenna-related aspects which serve as a foundational framework for future work considering that both communication and radar detection take place in the near field. We show adding an RF-feed to the meta-element incurs additional amplitude loss in the spectrum of interest. At the same time, increasing the number of radar antennas (i.e., elements with RF-feed) improves the radar angular accuracy.

A novel reconfigurable dielectric resonator antenna (DRA) employed a T-Shaped microstrip-fed structure in order to excite the dielectric resonator is presented. By carefully adjusting the location of the inverted U-shaped slot, switches, and length of arms, the proposed antenna can support WLAN wireless system. In addition, the presented DRA can be proper for cognitive radio because of availability switching between wideband and narrowband operation. The proposed reconfigurable DRA consisting of a Roger substrate with relative permittivity 3 and a size of 20 mm × 30 mm × 0.75 mm and a dielectric resonator (DR) with a thickness of 9 mm and the overall size of 18 mm × 18 mm. Moreover, the antenna has been fabricated and tested, which test results have enjoyed a good agreement with the simulated results. As well as this, the measured and simulated results show the reconfigurability that the proposed DRA provides a dual-mode operation and also three different resonance frequencies as a result of switching the place of arms.

A terahertz sensor structure is proposed that can sense any variations in analyte permittivity. The sensor essentially works according to the shifts in the resonance frequencies of its propagated spoof surface plasmonic modes. The proposed structure shows great support for surface plasmon oscillations, which is proved by the calculated dispersion diagram. To achieve this in terahertz frequencies, a metamaterial structure is presented in the form of a structure with two-dimensional periodic elements. Afterward, it is shown that the performance of the sensor can be affected by different parameters such as metal stripe thickness, length of metal stripe, and width of metal stripe as the most influential parameters. Each of the parameters mentioned can directly influence on the electric field confinement in the metal structure as well as the strength of propagation modes. Therefore, two propagation modes are compared, and the stronger mode is chosen for sensing purposes. The primary results proved that the quality factors of the resonances are substantially dependent on certain physical parameters. To illustrate this, a numerical parametric sweep on the thickness of the metal stripe is performed, and the output shows that only for some specific dimensions the electromagnetic local field binds strongly with the metal part. In a similar way, a sweeping analysis is run to reveal the outcome of the variation in analyte permittivity. In this section, the sensor demonstrates an average sensitivity value, ~1,550 GHz/Permittivity unit, for a permittivity range between 1 and 2.2, which includes the permittivity of many biological tissues in the terahertz spectrum. Following this, an analysis is presented, in the form of two contour plots, for two electrical parameters, maximum electric field and maximum surface current, based on 24 different paired values of metal thickness and metal width as the two most critical physical parameters. Using the plotted contour diagrams, which are estimated using the bi-harmonic fitting function, the best physical dimension for the maximum capability of the proposed sensor is achieved. As mentioned previously, the proposed sensor can be applied for biological sensing due to the simplicity of its fabrication and its performance.

This paper presents a single layer planar slot antenna for dual band operation. The antenna is fed by a coplanar waveguide (CPW) with two inverted C-shaped resonators to achieve the dual band operation. The impedance bandwidth for |S11| < -10dB is 14% in lower band and 7% in higher band. The antenna prototype's electromagnetic performance, impedance bandwidth, radiation pattern, and antenna gain were measured. The proposed configuration offers a relatively compact, easy to fabricate and dual band performance providing gain between 2 and 4 dBi. The designed antenna has good dual bandwidth covering 3.5 WiMAX and 5.8 WLAN tasks. Experimental and numerical results also showed good agreement after comparison. © 2014 Penerbit UTM Press. All rights reserved.

The effect of vehicle's proximity on the radiation pattern when the RADAR's antenna is mounted on the body of autonomous cars is analysed. Two directional radiation patterns with different specifications are placed at different locations of a realistic car body model. The simulation is performed based on ray-tracing method at 77 GHz, the standard frequency for selfdriving applications. It is shown that to obtain a robust RADAR sensor, the antenna radiation pattern is better to have relatively higher gain and lower side-lobe-level (SLL), than narrower half-power-beamwidth (HPBW) and higher front-to-back (F/B) ratio. Both academia and industry can benefit from this study.

— This paper presents a novel leaky-wave antenna based on utilizing the high bandwidth and low loss ridge gap waveguide concept, featuring a cosecant squared radiation pattern. The antenna is designed to operate within the frequency range of 25 GHz to 29 GHz. At the center frequency of 28 GHz, the antenna achieves a maximum gain of 10 dBi. Additionally, at a frequency of 28.8 GHz, the antenna exhibits a maximum return loss of-16.9 dB. Moreover, the proposed leaky-wave antenna demonstrates the potential of the radiation technology for 5G systems by enabling scanning angles ranging from approximately 5 ֯ to 20֯ across the specified frequency range. This feature highlights the versatility and suitability of the antenna for various applications in 5G communication systems.

This chapter has presented the insight methodologies on how to design, implement, and evaluate a width-bandwidth mm-wave fully connected hybrid beamforming metrological testbed with a large antenna array. The focus has been given on discussions include testbed design, calibration procedures, experimental evaluations, as well as the critical factors to consider for their practical implementation. If RF harmonics and spurious signal issues are avoided, one envisages that the testbed could be setup to work between 25 and 30 GHz with 2-GHz instantaneous bandwidth. Each of the phase shifters and attenuators in the mm-wave fully connected hybrid beamformer has six separate DIO control bits. Apart from describing the calibration procedures for the phase and amplitudes of the established fully connected hybrid beamformer system, the linearity, phase, and attenuation performance of the beamformer system between 25.5 and 26.5 GHz have been evaluated as well as the beamforming and link performance of a 128-element planar phased array at 26 GHz where the measured radiation patterns with and without amplitude tapering are compared.

A novel high-isolation, monostatic, circularly polarized (CP) simultaneous transmit and receive (STAR) anisotropic dielectric resonator antenna (DRA) is presented. The Proposed antenna is composed of two identical but orthogonally positioned annular sectoral anisotropic dielectric resonators. Each circularly polarized (CP) resonator consists of alternating stacked dielectric layers of relative permittivities of 2 and 15 and is excited by a coaxial probe from the two opposite ends to have left and right-hand CP. Proper element spacing and a square absorber are placed between the resonators to maximize Tx/Rx isolation. Such a structure provides an in-band full-duplex (IBFD) CP-DRA system. Measurement results exhibit high Tx/Rx isolation better than 50 dB over the desired operating bandwidth (5.87 to 5.97 GHz) with a peak gain of 5.49 and 5.08 dBic for Ports 1 and 2, respectively.

In this work it is demonstrated that substrate integrated waveguide longitudinal slotted array antenna (SIWLSAA) which is loaded with metal fences exhibits high-isolation across VHF/UHF bands. A reference SIWLSAA used for comparison purpose comprises of 3×63×6 slotted arrays constructed on the top and bottom sides of the FR-4 lossy substrate has maximum isolation of −63 dB between its radiation slots. Improvement in isolation is demonstrated using a simple new technique based on inserting a metal fence between each row of slot arrays. The resulting isolation is shown to be is better than −83 dB across 200 MHz to 1.0 GHz with gain greater than 1.5 dBi., and side-lobe level less than - 40 dB. The proposed SIWLSAA is compact and has dimensions of 40×10×540×10×5mm3 (0.026λ0×0.006λ0×0.002λ0) where λ0 is 200 MHz. The proposed structure should find application in multiple-input multiple-output (MIMO) and radar systems.

In this paper, a mathematical model is proposed to govern the phase distribution on a reconfigurable intelligent surface (RIS) for anomalously reflecting the beam towards the directions of interest. To this end, two operational modes are defined with respect to the reflected pattern. In the first mode, the RIS is configured to form multi-reflected beams toward the directions of interest capable of being controlled independently. The second mode is when the RIS provides a wide reflected beam. Regarding to each mode, a cost function is derived and then, in order to enhance the reflected pattern characteristics, a genetic algorithm (GA) is employed to the model as optimization method. To validate the practicality of the method, the proposed model is applied to a fabricated RIS to assess its performance in a real-world outdoor scenario. In the first mode, an asymmetric dual-beam reflected pattern is obtained and tested with tilt angles of θ0=60° and θ1=135°. Furthermore, a wide-reflected beam is generated in the second mode with half-power beamwidth of θHPBW=30° and tilt angle of θ0=75°. At both modes, the measured data are well aligned with the simulated results.

© 2006-2015 Asian Research Publishing Network (ARPN).Radial Line Slot Array Antenna has simple structure and exhibit good radiation characteristics. It is low cost, easy to manufacture with high gain and it found application in services like Direct Broadcast Services and Wireless LAN. Its features make it attractive for millimeter wave mobile broadband applications like the fifth generation (5G) mobile communication system. Also, it can be designed for circular, linear or elliptical polarization. But achieving a reduced sidelobes level has not been an easy task in its design. This paper presents a simple technique to improve the impedance bandwidth and reduce the sidelobes level in linearly polarized Radial Line Slot Array Antenna at 28 GHz for 5G mobile communication system. In the design, high frequency laminate RT duroid 5880 and air gap were utilized with a modified dielectric coated 50 O SSMA connector as the coaxial to waveguide transition. The technique was experimented via simulation on Computer Simulation Technology Microwave Studio 2014 software. The simulation result gave a return loss of -18.98 dB at 28 GHz. Gain of 23.3 dB, 10 dB impedance bandwidth of 1.28 GHz, sidelobes levels of: -16.5 dB (Eplane); -17.5 dB (H- plane) and efficiency of 96 % were also realized.

An ultra-wideband dielectric resonator antenna (DRA) is studied and investigated for wireless application. The dielectric resonator is fed by a microstrip line. The overall size of the proposed DR antenna is 20 × 35 mm2, and the thickness of the dielectric resonator is only 5.12 mm, which is suitable for mobile device. The design simulation is done by using computer simulation Technology Microwave studio suite 2012 (CST). The results represent that by using N-shaped dielectric resonator, a wideband impedance bandwidth of 111% for VSWR≤ 2 covering a frequency range from 3.59 to 12.61 GHz. A parametric study is presented. © 2013 IEEE.

© 2014 IEEE.This paper presents a Wideband Slot Antenna for 4G applications. The presented antenna includes a T-shape resonator fed by a coplanar waveguide (CPW). The prototype of the proposed antenna has been fabricated and measured results show that wideband operation has been obtained. The radiation characteristics of the offered antenna such as impedance bandwidth, gain and radiation pattern have been measured. The wideband frequency range from 1.72 GHz to 2.85 GHz has been achieved and covered several LTE bands.

In this paper, a compact, highly integrated multiplexing filtering antenna operating at 4.7/5.2/6.0/6.6 GHz is proposed for the first time. Different from traditional antennas, the proposed antenna has one shared radiator but four ports working in different frequency bands and thus, it can simultaneously support four different transmission channels. The proposed multiplexing antenna is composed of a patch with a U-shaped slot, two substrate integrated waveguide (SIW) cavities, and four resonator-based frequency-selective paths. The resonator-based paths can not only enhance the inter-channel isolations but also improve the impedance bandwidth. The design principles and the methods of controlling the four operating bands are studied. Measurement results agree reasonably well with the simulations, showing four channels from 4.5 to 4.8 GHz, 5.1 to 5.3 GHz, 5.85 to 6.3 GHz, and 6.4 to 6.6 GHz, respectively. The antenna also exhibits a high isolation of over 25 dB between the channels. In addition, the proposed antenna has a consistent broadside radiation pattern and polarization in the four bands, manifesting the proposed multiplexing filtering antenna can be a promising candidate for multi-service wireless communication systems.

Smart environments are expected to constitute a distributed wireless network that will support the physical and digital layers in a sustainable manner. Metasurfaces can be used to control radio waves in a way that is compliant with the current operation of wireless communications. In order to control wave propagation, we need a mathematical framework that captures the metasurface operation in the presence of the surrounding propagation environment. The scattering properties of such a complex propagation scenario need to be found self-consistently, i.e., requires a general method that captures multiple interactions between metasurface and environment. This translates into solving a Burton-Miller formulation for the associated boundary-value wave problem. Our methodology overcomes the non-uniqueness difficulties generated by inconsistent theories where the propagation problem and metasurface scattering are solved in isolation and then coupled afterward. Importantly, the use of the fast multipole method is adopted to improve the overall computational efficiency. Index Terms—Metasurface, wireless communication, physical layer, reconfigurable intelligent surface and smart skin.

Wearable antennas have gained much attention in recent years due to their attractive features and possibilities in enabling lightweight, flexible, low cost and portable wireless communication and sensing. Such antennas need to be conformal when used on different parts of the human body, thus need to be implemented using flexible materials and designed in a low profile structure. Ultimately, these antennas need to be capable of operating with minimum degradation in proximity to the human body. Such requirements render the design of wearable antennas challenging, especially when considering aspects such as their size compactness, effects of structural deformation and coupling to the body, and fabrication complexity and accuracy. Despite slight variations in severity according to applications, most of these issues exist in the context of body-worn implementation. This review aims to present the different challenges and issues in designing wearable antennas, their material selection, and fabrication techniques. More importantly, recent innovative methods in back radiations reduction techniques, circular polarization (CP) generation methods, dual polarization techniques and providing additional robustness against environmental effects are first presented. This is followed by a discussion of innovative features and their respective methods in alleviating these issues recently proposed by the scientific community researching in this field.

—In this paper, a reflecting metasurface is proposed to control the reflection angle by manipulating the chemical potential (CP) of graphene. The surface can operate in three anomalous reflection modes for θ = 45 • , 60 • and 75 • while it is illuminated with a normal incident electromagnetic wave (EMW). Moreover, by tuning the chemical potential of graphene sheets the proposed surface can switch off the reflection mode of operation by absorbing the incident EM power.

A new modified planar dielectric resonator antenna (DRA) is presented and investigated. The proposed DRA is excited by a microstrip feed that is extended as a probe in the proximity of the DR. On the opposite side to the probe excitation printed narrow strips directly connected to the ground plane edge are used to improve the radiation characteristics of the antenna by keeping a unidirectional broadside radiation. In addition, the short circuit strips introduce a second frequency band. Thus, a dual-band antenna is achieved. The measured bandwidths are about 73% (2.78-5.95 GHz) for the wideband DRA as well as 8% (2.4-2.6 GHz) and 56% (3.3-5.85 GHz) for the dual-band DRA. The minimum and maximum gain enhancements of about 0.6 and 1.2 dB from 3.5 to 6 GHz are obtained. Parametric study and measurement results are presented and discussed. © 2013 Wiley Periodicals, Inc.

A Ka-band inset-fed microstrip patches linear antenna array is presented for the fifth generation (5G) applications in different countries. The bandwidth is enhanced by stacking parasitic patches on top of each inset-fed patch. The array employs 16 elements in an H-plane new configuration. The radiating patches and their feed lines are arranged in an alternating out-of-phase 180-degree rotating sequence to decrease the mutual coupling and improve the radiation pattern symmetry. A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved with -15 dB reflection coefficients and 20 dB mutual coupling between the elements. With uniform amplitude distribution, a maximum broadside gain of 19.88 dBi is achieved. Scanning the main beam to 49.5◦ from the broadside achieved 18.7 dBi gain with -12.1 dB sidelobe level (SLL). These characteristics are in good agreement with the simulations, rendering the antenna to be a good candidate for 5G applications.

In this paper, a compact, broadband, planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications. The antenna element is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter. The two dipoles are placed side-by-side at both sides of the SIC and they are compensated with each other to form an omni-directional pattern in horizontal plane. By properly combing the resonant frequencies of the dipoles and the SIC, a wide impedance bandwidth from 24 to 29.5 GHz is achieved. To realize a large array while reducing the complexity, loss and size of the feeding network, a novel dual-port structure combined with radiation and power splitting functions is proposed for the 1st time. The amplitude and phase on each element of the array can be tuned, and therefore, the grating lobes level can be significantly reduced. Based on the dual-port structure, an 8-element array with an enhanced gain of over 12 dBi is designed and prototyped. The proposed antenna also features low profile, low weight and low cost, which is desirable for 5G commercial applications. Measured results agree well with the simulations, showing that the proposed high-gain array antenna has a broad bandwidth, omni-directional pattern in horizontal plane, and low side-lobes.

The characteristics of indoor transparent antenna are investigated. The purpose of the antenna is applied for television signal reception which is operating at Ultra High Frequency band. The antenna was made from silver coated polyester film (AgHT-4), the transparent con-ductive material and it is attached on a layer of glass substrate. The antenna size has width and length of 120mm × 150 mm. It was fed by a co-planar waveguide due to the opportunity of low ra-diation loss and to reduce reflection of the antenna. The frequency range of 500MHz to 800MHz is chosen as it is the UHF television reception band and allocated by Federal Communications Commission. Due to the television station provided in Malaysia, each station have different channel with its own specification frequencies. The channels also are based on the transmitter base station location. Since the proposed project launches at Universiti Teknologi Malaysia, Skudai, Johor, Malaysia so all the channel is following the frequency from GunungPulai, Johor transmitter base station. The channel utilizations are Channel 55 (742-750 MHz): TV1, Chan-nel 26 (510-518 MHz): TV3, Channel 42 (638-646 MHz): NTV7, Channel 44 (654-662 MHz): TV9 and Channel 46 (670-678 MHz): 8TV. Then, the proposed antenna was designed by using Computer Simulation Software (CST) Microwave Studio to obtain the simulation result. The simulated bandwidth of the antenna obtained is 448MHz (502MHz to 950 MHz) with bandwidth of 61.71%. It has a potential to be realized for TV reception because of the omni-directional radiation pattern and gain is more than 2.0 dBi.

A novel compact ultrawideband (UWB) dielectric resonator antenna (DRA) with a band rejection at 5.8 GHz is proposed and studied. The antenna is composed of a thin monopole printed antenna loaded with DR that is housed into a dielectric substrate and an L-shaped parasitic strip connected to the ground plane. The L-shaped strip andmetallic sheet are utilized to improve impedance bandwidth. A modified metallic sheet underneath the dielectric resonator has been applied to create a band rejection at frequency 5.8 GHz. The measurement results exhibit acceptable performances in terms of reflection coefficient, radiation pattern, efficiency, and realized gain. © 2013 IEEE.

A novel mathematical approach is proposed for the placement of unit-cells at digital metasurfaces with applications in holography, imaging, coverage improvement and antenna array. As a proof of concept, the idea is applied to a simple unit-cell capable of providing 180 degrees of phase difference between two states of it. Used unit-cell is working at 90GHz although the idea can be used in any other frequencies. It has been shown that the proposed method is capable of providing better results compare to conventional techniques in terms of concentration of intensity and quality of produced field pattern.

A wideband and compact circularly polarized (CP) C-shaped dielectric resonator antenna (DRA) is presented and investigated. The proposed C-shaped DR is excited by a simple stripe line connected to a coplanar waveguide (CPW) feeding line. The C-shaped DRA is circularly polarized with 19% axial ratio (AR) bandwidth. It is found that the CP bandwidth can be expanded by using a narrow short circuit strip. The final design achieves CP with 50% AR bandwidth. The proposed circularly polarized DRA (CPDRA) with good radiation characteristics offers an impedance bandwidth of 58% between 3.45 and 6.26 GHz for VSWR ≤ 2. The proposed DRA is fabricated and tested. Very good agreement between simulated and measured results is obtained.

A Ka-band inset-fed microstrip patches linear antenna array is presented for the fifth generation (5G) applications in different countries. The bandwidth is enhanced by stacking parasitic patches on top of each inset-fed patch. The array employs 16 elements in an H-plane new configuration. The radiating patches and their feed lines are arranged in an alternating out-of-phase 180-degree rotating sequence to decrease the mutual coupling and improve the radiation pattern symmetry. A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved with -15 dB reflection coefficients and 20 dB mutual coupling between the elements. With uniform amplitude distribution, a maximum broadside gain of 19.88 dBi is achieved. Scanning the main beam to 49.5° from the broadside achieved 18.7 dBi gain with -12.1 dB sidelobe level (SLL). These characteristics are in good agreement with the simulations, rendering the antenna to be a good candidate for 5G applications.

This paper presents a new approach to suppress interference between neighbouring radiating elements resulting from surface wave currents. The proposed technique will enable the realization of low-profile implementation of highly dense antenna configuration necessary in SAR and MIMO communication systems. Unlike other conventional techniques of mutual coupling suppression where a decoupling slab is located between the radiating antennas the proposed technique is simpler and only requires embedding linear slots near the periphery of the patch. Attributes of this technique are (i) significant improvement in the maximum isolation between the adjacent antennas by 26.7 dB in X-band and >15 dB in Ku and K-bands; (ii) reduction in edge-to-edge gap between antennas to 10 mm (0.37 λ); and (iii) improvement in gain by >40% over certain angular directions, which varies between 4.5 dBi and 8.2 dBi. The proposed technique is simple to implement at low cost.

A Rectangular Dielectric Resonator Antenna (RDRA) made of a high permittivity (ε r = 30) ceramic material is presented. It is shown that by selecting the resonator shape and creating a L-shape hole inside the dielectric resonator, it is possible to design RDRA which compact size and wide frequency coverage. The radiation characteristics of the RDRA are broad and stable across a matching band of 3.6 to 9.6 GHz. Also, left hand circular polarization (LHCP) is occurred in the center frequency of 4.3 GHz. The proposed antenna has good radiation characteristics over the operating bandwidth. © 2011 IEEE.

New modified 2 × 2 and 3 × 3 series-fed patch antenna arrays with beam-steering capability are designed and fabricated for 28-GHz millimeter-wave applications. In the designs, the patches are connected to each other continuously and in symmetric 2-D format using the high-impedance microstrip lines. In the first design, 3-D beam-scanning range of ± 25° and good radiation and impedance characteristics were attained by using only one phase shifter. In the second one, a new mechanism is introduced to reduce the number of the feed ports and the related phase shifters (from default number 2 N to the reduced number N + 1 in the serial feed (here N = 3) and then the cost, complexity, and size of the design. Here, good scanning performance of a range of ± 20°, acceptable sidelobe level, and gain of 15.6 dB are obtained. These features allow to use additional integrated circuits to improve the gain and performance. A comparison to the conventional array without modification is done. The measured and simulated results and discussions are presented.

This paper presents circular-shape monopole antenna for wireless body area net-work (WBAN) applications at 3.1 to 5.1 GHz and 6.5 to 8 GHz. The design and simulation of proposed antenna for WBAN applications in the free space and close proximity of body surface has been done by using CST Microwave Studio. The proposed antenna was designed on FR4 substrate with dielectric constant (εr) of 4.4 and thickness of 1.6 mm. The final optimized design is 50 × 40mm2. The simulated current distribution on the radiating patch for the proposed circular-shaped monopole antenna frequencies of 3.3 and 7.5 GHz in the free space is presented. The size of circular-shape monopole antenna it is suitable for WBAN application.

A compact size, dual-band wearable antenna for off-body communication operating at the both 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band is presented. The antenna is a printed monopole on an FR4 substrate with a modified loaded ground plane to make the antenna profile compact. Antennas’ radiation characteristics have been optimized while the proposed antenna placed close to the human forearm. The fabricated antenna operating on the forearm has been measured to verify the simulation results.

© 2015, Electromagnetics Academy. All Rights Reserved.A novel design for a transparent circularly polarized circular slot antenna fed by a coplanar waveguide (CPW) is presented in this paper. The circular polarization is achieved by introducing a tapered split gap in the ring patch of the circular slot antenna in combination with unequal CPW ground arms. The antenna is designed using AgHT-4 laminated on a 2mm thick glass with a relative permittivity of 7. The proposed antenna is designed to operate at 5.8 GHz for WLAN applications. The tapered split gap and inequality in the lengths of the CPW ground arms contribute to a 3 dB axial ratio bandwidth from 5.4 to 6.2GHz. The proposed antenna has been studied theoretically and fabricated. The measured results show that the proposed antenna has a gain of 0.92 dB at 5.8 GHz. Reflection coefficient (S11), axial ratio (AR), and radiation patterns are presented and briefly discussed.

A tunable circularly polarized ferrite-based antenna array is proposed to estimate the direction of received signals without ambiguity using the applied magnetic bias to rotate the far-field phase pattern around the antenna boresight. The proposed structure can be implemented in a small area because of low coupling between antenna elements and it is capable of estimating the direction of arrival for signals coming from ±40 • respect to the body coordinate of structure. This simple and compact direction finder structure is easy to fabricate and the proposed algorithm is frequency independent.

A metasurface-based thin flat lens operating at millimeter wave frequencies is presented. The three-layered Huygen Metalens indicates collimating/focusing of broadband frequencies from 60 to 74 GHz, with a gain enhancement of 22.5 dBi at a central frequency of 69 GHz while fed by a dipole antenna. The metasurface transmission performance is designed and simulated by numerical and analytical approaches. By integrating multilayered 1-bit Huygens unit cells, the metasurface produced 180 0 phase coverage with constant high amplitude. The proposed design comprised of 50 × 50 unilcells, creating an area of 75 × 75mm 2. The dipole antenna is applied to illuminate the proposed metasurface where the distance between the feeder and metalens is 27 mm. The result shows that the proposed metalens antenna achieves a maximum gain of 25 dBi at 69GHz GHz. The unique features of the proposed lightweight metalens will be widely used in wireless communication system for mmW wave frequencies.

A two-port MIMO Dielectric Resonator Antenna (DRA) has been proposed and studied. The antenna consists of a single Rectangular DRA (RDRA) element housed in a thin FR4 substrate, that is fed by two microstrip feed lines. Both the feeding lines excite (Formula presented.) mode in the RDRA. The mutual coupling between the ports has been decreased by employing two symmetrical slits in the ground plane. The proposed antenna has been fabricated and a parametric study has been carried out to obtain the optimum parameters. The presented antenna with acceptable MIMO characteristics, covers a measured bandwidth of 80 MHz (2.56–2.64 GHz) for |S11| < −10 dB, which is able to operate on LTE band 38. The measured isolation between the two ports for the desired frequency band is better than 20 dB. The presented antenna has been examined by calculating and measuring the Envelope Correlation Coefficient, Mean Effective Gains and the Diversity Gain. Based on the study that has been carried out, the antenna offers easy fabrication, feeding and good MIMO characteristics. Therefore, the presented antenna can be a suitable candidate for LTE applications.

Current trends in developing cost-effective and energy-efficient wireless systems operating at millimeter-wave (mm-wave) frequencies and with large-scale phased array antennas for fulfilling the high data-rate demands of 5G and beyond has driven the needs to explore the use of hybrid beamforming technologies. This paper presents an experimental study of a wide-bandwidth millimeter-wave fully-connected hybrid beamformer system that operates at 26 GHz with 128 antenna elements arranged in a 16 x 8 planar array, 6-bit phase shifter, 6-bit attenuators and two separate radio frequency (RF) channels each capable of fully independent beamforming. The linearity, phase, and attenuation performance of the beamformer system between 25.5 GHz and 26.5 GHz are evaluated as well as the beamforming performance of a 128-element planar phased array at 26 GHz where the measured radiation patterns with and without amplitude tapering are compared.

In this paper, an ultra-wideband Terahertz (THz) channel measurement campaign in the 500-750 GHz frequency band is presented. Power levels received from signal transmission by reflections off 14 different materials were measured in an indoor environment at Non-Line-of-Sight (NLoS) between the Transmitter (Tx) and Receiver (Rx), and compared to power levels received at Line-of-Sight (LoS) transmission. Frequency up-converters were used to transmit the signal using 26 dBi horn antennas at the Tx and Rx side and the signal was measured using a Vector Network Analyzer (VNA). From the data collected, the signal losses due to absorption and diffuse scattering from the rough surface of each Material Under Test (MUT) are calculated. The power delay profile (PDP) is presented, where multipath clustering due to diffuse scattering is observed for materials which have a high frequency selectivity, while less scattering and mostly specular reflection is shown for materials with low frequency selectivity.

A wideband and compact circularly polarized (CP) C-shaped dielectric resonator antenna (DRA) is presented. The proposed C-shaped DR is excited by a microstrip feed in one side of the dielectric substrate. DR is housed inside the thin dielectric substrate above the vertical ground plane edge. By using one narrow short circuit strip, CP bandwidth of the proposed antenna is enhanced. The final design achieves CP with 44% axial ratio (AR) bandwidth. The proposed circularly polarized DRA with good radiation characteristics offers an impedance bandwidth of 67% between 3.35 and 6.76GHz for VSWR < 2. © 2013 IEEE.

As future communication systems move toward the terahertz (THz) spectrum with a much higher speed and more densification, enhanced security utilizing the novel concepts will be inevitable, particularly in automated identification systems. This paper proposes a novel spatial domain technique based on vortex beams generated by metasurface structures for efficient chipless identification (ID) sensors where the information is saved in the vortex modes. This approach using the vortex concept offers the high security strength in the automated systems compared to existing solutions, including time-based and frequency-based sensors. Furthermore, combining these vortex-based sensors and conventional ones results in substantially increasing the stored information capacity. To verify the idea, here, we present an uneven dielectric metasurface (UDM) to generate distinct vortex modes to identify different information. The proposed sensor is designed by using an equivalent transmission line (TL) model, and the extracted results exhibited a good agreement between simulation and theoretical approaches. Furthermore, it is demonstrated that the transmitted information capacity can be notably enhanced by using a sensor tag with simultaneous multiple modes and also using more than one tag simultaneously.

This paper presents the findings of a steerable higher-order mode (TEy1δ3) dielectric resonator antenna with parasitic elements. The beam steering was successfully achieved by switching the termination capacitor on the parasitic element. In this light, all of the dielectric resonator antennas (DRAs) have the same dielectric permittivity similar to that of 10 and was excited by a 50Ω microstrip with a narrow aperture. The effect of the mutual coupling on the radiation pattern and the reflection coefficient, as well as the array factor were investigated clearly using MATLAB ver. 2014b and ANSYS HFSS ver. 16. As the result, the antenna beam of the proposed DRA array managed to steer from -32° to +32° at 15 GHz. Furthermore, the measured antenna array showed the maximum gain of 9.25 dBi and the reflection coefficients which are less than -10 dB with the bandwidth more than 1.3 GHz, which is viewed as desirable for Device-to-Device communication (D2D) in 5G Internet of Things (IoT) applications.

A beam steering (up to 36 degrees) high gain (20.5 dBi) Leaky-Wave Antenna (LWA) is presented at 26 GHz for enhanced data rate in millimeter wave (mm-wave) 5G system in dynamic environments. A low loss (

An ultra-wideband dielectric resonator antenna (DRA) with enhanced gain is presented and investigated for wireless applications. The antenna has a compact shape with UWB characteristics. The radiator's structure is a split Z-shaped DRA with dielectric constant (εr) of 10. The antenna is mounted on a copper ground plane of size 75 × 90mm2 and is fed by a split bevel-shaped strip to improve the impedance matching. Also, an air gap has been introduced between DR and ground plane to reduce the Q factor and dielectric constant, which in turn improves the impedance bandwidth. Extensive parametric studies have been carried out on different parameters in order to achieve an optimum structure. Ansoft HFSS v14 has been used for the simulation of the proposed antenna. The simulated results show that the antenna can efficiently operate over the frequency range from 2.5 GHz to 10.6 GHz covering the entire UWB range.

In this letter, a dual-band 8x8 MIMO antenna that operates in the sub-6 GHz spectrum for future 5G multiple-input multiple-output (MIMO) smartphone applications is presented. The design consists of a fully grounded plane with closely spaced orthogonal pairs of antennas placed symmetrically along the long edges and on the corners of the smartphone. The orthogonal pairs are connected by a 7.8 mm short neutral line for mutual coupling reduction at both bands. Each antenna element consists of a folded monopole with dimensions 17.85 x 5mm2 and can operate in 3100-3850 MHz for the low band and 4800-6000 MHz for the high band ([S11] ˂ -10dB). The fabricated antenna prototype is tested and offers good performance in terms of Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), total efficiency and channel capacity. Finally, the user effects on the antenna and the Specific Absorption Rate (SAR) are also presented.

© 2015 Penerbit UTM Press. All rights reserved.This paper presents the design of coplanar waveguide (CPW) rectangular dielectric resonator antenna (RDRA) with and without metallic strip, operating at 2.6 GHz for long term evolution (LTE) applications. The CPW RDRA without metallic strip produces impedance bandwidth of 51 %. Then, a metallic strip was added on top of the dielectric resonator (DR) in order to enhance the impedance bandwidth; thus give more flexibility for the system to cover more applications. A good agreement between simulation and measurement results, in terms of reflection coefficient magnitude and radiation pattern is presented. The simulated and measured impedance BWs for S11

A simple, compact, wideband rectangular dielectric resonator antenna (RDRA) is presented. The bandwidth is enhanced using a proper tapered strip excitation from one side of the DR. The radiation characteristics are improved by adding a shorted narrow strip to the opposite side of the excitation. In addition, by using this shorted strip, further improvement of the bandwidth is obtained. A parametric study on the strip dimension is carried out. The proposed DRA with good radiation characteristics offers a measured bandwidth of 96% between 2.13 and 6.08 GHz for VSWR < 2. © 2010 IEEE.

This paper investigates the impact of intelligent reflecting surface (IRS) enabled wireless secure transmission. Specifically, an IRS is deployed to assist multiple-input multiple-output (MIMO) secure system to enhance the secrecy performance, and artificial noise (AN) is employed to introduce interference to degrade the reception of the eavesdropper. To improve the secrecy performance, we aim to maximize the achievable secrecy rate, subject to the transmit power constraint, by jointly designing the precoding of the secure transmission, the AN jamming, and the reflecting phase shift of the IRS. We first propose an alternative optimization algorithm (i.e., block coordinate descent (BCD) algorithm) to tackle the non-convexity of the formulated problem. This is made by deriving the transmit precoding and AN matrices via the Lagrange dual method and the phase shifts by the Majorization-Minimization (MM) algorithm. Our analysis reveals that the proposed BCD algorithm converges in a monotonically non-decreasing manner which leads to guaranteed optimal solution. Finally, we provide numerical results to validate the secrecy performance enhancement of the proposed scheme in comparison to the benchmark schemes.

A hybrid technique is proposed to manipulate the feld distribution in a substrate integrated waveguide (SIW) H-plane horn to enhance its radiation characteristics. The technique comprises two cascaded steps to govern the guided waves in the structure. The frst step is to correct the phase of felds and form a quasi-uniform distribution in the fare section so that the gain increases and sidelobe-level (SLL) decreases. This is obtained by loading the structure with a novel modulated metal-via lens. Field expansion on the radiating aperture of the SIW H-plane horn generates backward surface waves on both broad walls which increases the backlobe. In the second step, these backward surface waves are recycled and directed forward with the aid of holography theory. This is achieved by adding a couple of dielectric slabs with holographic-based patterns of metallic strips on both broad walls. With this step, the backlobe is reduced and the endfre gain is further increased. Using the proposed technique, the structure is designed and fabricated to operate at f = 30GHz which simultaneously improves the measured values of gain to 11.65 dBi, H-plane SLL to − 17.94 dB, and front-to-back ratio to 17.02 dB.

A simple-structure probe-fed multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) is designed for sub-6GHz applications with a reduced inter-element spacing (< 0.5λ). A 4-element rectangular DRA is positioned in a compact space verifying the proposed DRA potential for MIMO applications. Each element consists of two dielectric resonators with different permittivity of 5 and 10, excited by the coaxial probe. The measurement results reveal that the proposed MIMO DRA provides an envelope correlation coefficient (ECC) of less than 0.01 with good MIMO performance.

A new single-fed circularly polarized dielectric resonator antenna (CP-DRA) without beam squint is presented. The DRA comprises an S-shaped dielectric resonator (SDR) with a metalized edge and two rectangular dielectric resonators (RDRs) blocks. Horizontal extension section is applied as an extension of the SDR, and a vertical-section is placed in parallel to the metallic edge. A vertical coaxial probe is used to excite the SDR and the vertical RDR blocks through an S-shaped metal element and a small rectangular metal strip. The two added RDRs that form an L-shaped DR improve the radiation characteristics and compensate for the beam squint errors. A wideband CP performance is achieved due to the excitation of several orthogonal modes such as [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. The experimental results demonstrate an impedance bandwidth of approximately [Formula: see text] (3.71-7.45 GHz) and a 3-dB axial-ratio (AR) bandwidth of about [Formula: see text] (3.72-6.53 GHz) with a stable broadside beam achieving a measured peak gain of about [Formula: see text]. Furthermore, a 100% correction in beam squint value from [Formula: see text] to [Formula: see text] with respect to the antenna boresight is achieved.

In this article, ultra-wideband (UWB) monopole antenna with circular polarization (CP) is designed and implemented. The proposed antenna consists of an asymmetric shaped radiator fed by a microstrip line and a limited ground plane on the back side of the substrate. The overall size of proposed antenna is 28 mm × 29 mm, which is suitable for mobile devices. The antenna is fabricated on inexpensive FR4 a dielectric constant of, loss tangent tan = 0.019 with thickness of 1.6-mm. The measured results show that the proposed monopole antenna has a very wide bandwidth from 2.98 to 10.93 GHz that covers the UWB application range and defined by 10-dB return loss. Furthermore, a very wide CP bandwidth of 3-dB axial ratio bandwidth that ranges from 7.18 to 10.01 GHz is achieved. © 2012 Wiley Periodicals, Inc.

A multifunctional antenna with diverse radiation patterns in different frequency bands (2.45/5.8 GHz) is presented in this paper. The antenna has a low profile but exhibits an omni-directional radiation pattern in the low-band operation and uni-directional pattern in the high-band operation. For the high-band operation, a 2 x 2 patch arrays are designed by employing an out-of-phase feeding method. The low-band operation with the omni-directional pattern is achieved by exciting four open-ended slots in-phase. The four slots are slit in the ground of the high-band array and in this way, this footprint of the antenna is maintained. The operating principles of the antenna are studied with the aid of equivalent circuit model and the current distribution. The antenna is prototyped and measured, demonstrating good results in terms of bandwidths, inter-channel isolation, radiation characteristics.

Conference Title: 2022 16th European Conference on Antennas and Propagation (EuCAP) Conference Start Date: 2022, March 27 Conference End Date: 2022, April 1 Conference Location: Madrid, SpainA detailed analysis of the performance of traditional machine learning and deep learning techniques applied on a representative classification problem of millimeter-wave (mmW) images is presented in this paper. The algorithms chosen for this analysis are the k-Nearest Neighbors (KNN), Random Forest (RF) and Convolutional Neural Network (CNN). All algorithms presented here are modeled using ‘keras’ library inside TensorFlow and ‘scikit-learn’ module. The dataset for training and testing are generated via a developed near-field coded aperture computational imaging (CI) physical model. The use of a physical model of an imaging system that implements CI techniques instead of an experimental set-up makes the whole dataset generation process facile and less time consuming. The training data, in case of the RF and KNN algorithms, are presented in tabular form whereas for the CNN technique, the synthesized images from the physical model itself are used for training. The models are tested with both synthesized as well as experimental data, generated from the physical model and a mmW handheld imager, respectively. Upon testing, it is observed that the KNN and RF algorithms are able to classify the test samples with accuracies of 82% and 87%, respectively, whereas an accuracy of 90% is observed in case of the CNN classifier. Also, an inference speed test is conducted on all the three algorithms. It was observed that CNN is the fastest to predict classes for all of the test samples with a frame rate of 3.8 ms/sample whereas RF is the slowest, with a frame rate of 65.9 ms/sample. These findings establish the fact that when it comes to image classification, CNN based classifiers perform better than any traditional machine learning algorithms with more accurate and faster predictions, paving the way for various real-time applications such as automatic threat detection.

This letter presents a systematic method to regulating the response of an artificial impedance surface. The method is based on governing the dispersion diagram to control the depth of modulation so that a meaningful pattern of scatterers is obtained on the structure. The method is applied on a holographic-based large reflective metasurface to achieve a dual-beam radiation pattern with tilt angles of \pm 45^{\circ } in the azimuth plane at f=3.5 GHz. The structure is fabricated and the measured data concur with the simulation results.

In this paper a novel design procedure to obtain wideband and small size dielectric antennas using high dielectric constant material is described. It is shown that by selecting the resonator shape and creating a notch on the dielectric resonator, it is possible to design rectangular dielectric resonator antenna which compact size and wide frequency coverage. Simple formulas are presented to illustrate the design procedure and allow a quick dimensioning of the antenna. Utilizing the proposed configuration and skillfully varying its aspect ratio, an appropriate structure is obtained that illustrates more than 47.03% impedance bandwidth (for VSWR< 2) at 4.39 to 7.09GHz frequency band. © 2010 IEEE.

One of the most controversial issues in Reconfig-urable Intelligent Surfaces (RIS) is how to localize users. A potential solution is to integrate sensing and communication into the RIS platform to simultaneously detect a target and establish a communication link. By utilizing a shared spectrum, it is possible to optimize the channel with little to no mutual interference. To this end, a hybrid metasurface layout is proposed that supports beamforming while also enabling the sensing of incident signals from the user. This hybrid technology couples a small portion of the incident signal into a sensing layer. In the next step, a sensing scheme is introduced that leverages the inherent multiplexing of information within the metasurface's substrate to retrieve relevant information using a few sensing elements. The proposed metasurface can generate desired radiation patterns, and the addition of sensing capabilities has minimal impact on its primary functionality.

This paper presents a novel design of trapped microstrip-ridge gap waveguide by using partially filled air gaps in a conventional microstrip-ridge gap waveguide. The proposed method offers an applicable solution to obviate frustrating assembly processes for standalone high-frequency circuits employing the low temperature co-fired ceramics technology which supports buried cavities. To show the practicality of the proposed approach, propagation characteristics of both trapped microstrip and microstrip-ridge gap waveguide are compared first. Then, a right-angle bend is introduced, followed by designing a power divider. These components are used to feed a linear 4-element array antenna. The bandwidth of the proposed array is 13 GHz from 64~76 GHz and provides the realized gain of over 10 dBi and the total efficiency of about 80% throughout the operational band. The antenna is an appropriate candidate for upper bands of WiGig (63.72~70.2) and FCC-approved 70 GHz band (71~76 GHz) applications.

In this paper, a high flat gain waveguide-fed aperture antenna has been proposed. For this purpose, two layers of FR4 dielectric as superstrates have been located in front of the aperture to enhance the bandwidth and the gain of the antenna. Moreover, a conductive shield, which is connected to the edges of the ground plane and surrounding aperture and superstrates, applied to the proposed structure to improve its radiation characteristics. The proposed antenna has been simulated with HFSS and optimized with parametric study and the following results have been obtained. The maximum gain of 13.0 dBi and 0.5-dBi gain bandwidth of 25.9 % (8.96 - 11.63 GHz) has been achieved. The 3-dBi gain bandwidth of the proposed antenna is 40.7% (8.07-12.20 GHz), which has a suitable reflection coefficient (

Digital metasurfaces have opened unprecedented ways to accomplish novel electromagnetic devices thanks to their simple manipulation of electromagnetic waves. However, the metasurfaces leveraging phase-only or amplitude-only modulation restricted the full-functionality control of the devices. Herein, a digital graphene-based metasurfaces engineering wavefront amplitude and phase are proposed for the first time to tackle this challenge in the terahertz (THz) band. The concept and its significance are verified using reprogrammable multi-focal meta-lens based on a 2/2-bit digital unit cell with independent control of 2-bit states of amplitude and phase individually. Moreover, we introduce a novel method to directly transmit digital information over multiple channels via the reprogrammable digital metasurface. Since these metasurfaces are composed of digital building blocks, the digital information can be directly modulated to the metasurface by selecting specific digital sequences and sent them to predetermined receivers distributed in the focal points. Following that, a multi-channel THz high-speed communication system and its application to build three-dimensional wireless agile interconnection are demonstrated. The presented method provides a new architecture for wireless communications without using complicated components of conventional systems. This work motivates versatile meta-devices in many applications envisioned for the THz frequencies, which will play a vital role in modern communications.

A novel P-shaped dielectric resonator antenna (DRA) is presented and investigated for wideband wireless application. By using P-shaped resonator, a wideband impedance bandwidth of 80 % from 3.5 to 8.2 GHz is achieved. The antenna covers all of wireless systems like C-band, 5.2, 5.5 & 5.8 GHz-WLAN & WiMAX. The proposed antenna has a low profile and the thickness of the resonator is only 5.12 mm, which is 0.06-0.14 free space wavelength. A parametric study is presented. The proposed DRA is built and the characteristics of the antenna are measured. Very good agreement between numerical and measured results is obtained.

In this communication, a low-cost, single-pole double-throw (SPDT) filtering radio frequency (RF) switch based on coupled resonators is proposed and utilized in a novel pattern reconfigurable antenna design. The proposed filtering switch employs two second-order quarter-wavelength microstrip resonant structures which can be controlled by p-i-n diodes, respectively. Compared with traditional switches based on p-i-n diode, this filtering switch can not only improve the RF response but also suppress the high-order harmonic, when it is used with an antenna. Then, a low-profile dual-port broadside/conical dual-mode antenna is proposed by embedding a slotted substrate integrated waveguide (SIW) cavity in the middle of a patch antenna. The slotted cavity is to realize the radiation in the broadside whereas the patch is fed by two probes in-phase to realize the conical radiation. Finally, the filtering switch and the dual-mode antenna are combined to realize the pattern reconfigurable antenna. By controlling the states of the p-i-n diodes, broadside and conical radiation patterns can be easily switched. The concept of switch-based pattern reconfigurable antenna is prototyped and experimentally verified. Measured results agree with the simulations, demonstrating a promising solution for pattern reconfigurable antenna designs.

In this paper, a controllable hybrid plasmonic integrated circuit (CHPIC) composed of hybrid plasmonic waveguide (HPW)-based rhombic nano-antenna, polarization beam splitter, coupler, filter, and sensor has been designed and investigated for the first time. In order to control the power into a corresponding input port, a graphene-based 1 × 3 power splitter with switchable output has been exploited. The functionality of each device has been studied comprehensively based on the finite element method and the advantages over state-of-the-art have been compared. Moreover, the effect of connection of CHPIC to the photonic and plasmonic waveguides has been studied to exhibit the capability of variety excitation methods of the CHPIC. Furthermore, the performance of the proposed CHPIC connected to inter/intra wireless transmission links has been investigated. The wireless transmission link consists of two HPW-based nano-antennas as transmitter and receiver with the maximum gain and directivity of 10 dB and 10.2 dBi, respectively, at 193.5 THz. The suggested CHPIC can be used for applications such as optical wireless communication and inter/intra-chip optical interconnects.

In this paper, for the first time, the idea of a dielectric director has been utilized to improve the directivity and gain of the proposed hybrid plasmonic rhombic nano-antenna (HPRNA). The proposed HPRNA can support a horizontal radiation pattern to flourish the concept of wireless transmission link. The horizontal radiation pattern has a 3 dB beamwidth of 43.5°, side lobe level of −11.9 dB, and a directivity and gain of 10.5 dBi and 10.3 dB, respectively, at the operating frequency of 193.5 THz. Moreover, the effects of geometric parameters to verify the functionality of the proposed nano-antenna have been investigated. Finally, the idea of an on-chip wireless transmission link based on transmitting and receiving HPRNAs has been developed and studied theoretically and numerically. The fabrication of the proposed nano-antenna can be done by the typical e-beam lithography (EBL) technique, which is easier than the complicated X-ray method because of its suitable aspect ratio.

A novel hybrid dielectric resonator antenna (DRA) excited by a printed monopole antenna is proposed and implemented. This new microstrip-fed fork-like stepped monopole antenna is designed to obtain a wide impedance bandwidth from 2 to 6 GHz. A quad-band characteristic is achieved by incorporating two modified cylindrical dielectric resonators with a high dielectric constant of 80, on top of the monopole exciter. Measured results demonstrated that the proposed DRA can be used in multiband wireless operations, covering GSM, PCS, UMTS, WLAN, and WiMax systems, from 1.75 to 5.85 GHz. Experimental and simulation results show a good agreement. © 2011 Wiley Periodicals, Inc.

The papers in this special section bring together the antenna community to present the state-of-the-art research conducted in this field and highlight the emerging antenna technologies in addressing the Earth and planetary science instrumentation. These papers aim to present some examples of the latest advances in antenna technology for Earth and planetary science. Among these antenna topologies, a particular emphasis should be given to metasurface type of antennas. A metasurface can be considered a 2-D surface synthesized using an array of subwavelength-sized unit-cells. Such surfaces can manipulate the behavior of EM waves to achieve the desired transmission, reflection, polarization, and radiation responses. Particularly, operating in a reflection mode, such surfaces have received substantial interest in the context of reflectrarrays. Pelletier et al. present a dual-polarized reflectarray antenna operating at Ku-band frequencies to synthesize a synthetic aperture radar (SAR) for snow mass measurements.

In this paper, a graphene-based terahertz (THz) absorber is presented using neural networks. The proposed structure contains graphene, which supports plasmon resonance, and provides tunable properties at the THz regime. Thus, applying a bias voltage to the designed absorber results in various frequency responses in the THz frequency spectrum. In order to predict the structural geometry of the proposed absorber in a fast and accurate way, artificial intelligence (AI) is employed. AI enables the possibility of designing a tunable THz absorber (when there is no limitation on applied bias voltage) and under a specific bias voltage. Several simulations using electromagnetic software have been conducted to generate a dataset for training the neural network. The resultant weights are then applied to define the absorbers' structures.

A multiple-input-multiple-output (MIMO) rectangular dielectric resonator antenna (RDRA) for 2.6-GHz Long Term Evolution (LTE) applications is investigated and presented. Two orthogonal modes of the RDRA are excited by using two different feed mechanisms: coplanar waveguide (CPW) and coaxial probe. The measured impedance bandwidth for port 1 and port 2 is 47% (2.09-3.38 GHz) and 25% (2.40-3.09 GHz), respectively. The measured correlation coefficient is 0.03 with nearly 10 dB diversity gain at frequency 2.6 GHz. The MIMO RDRA gives isoltion of above 20 dB over the operating frequency. The gain of 4.97 dBi is obtained for port 1 and 4.51 dBi for port 2 at 2.6 GHz. The S-parameters, isolation, gain, correlation coefficient, and diversity gain of the MIMO RDRA are studied, and reasonable agreement between the measured and simulated results is observed. © 2002-2011 IEEE.

This paper presents two different designs for frequency reconfigurable antennas capable of continuous tuning. The radiator, for both antenna designs, is a microstrip patch, formed from liquid metal, contained within a microfluidic channel structure. Both patch designs are aperture fed. The microfluidic channel structures are made from polydimethylsiloxane (PDMS). The microfluidic channel structure for the first design has a meander layout and incorporates rows of posts. The simulated antenna provides a frequency tuning range of approximately 118% (i.e. 4.36 GHz) over the frequency range from 1.51 GHz to 5.87 GHz. An experimental result for the fully filled case shows a resonance at 1.49 GHz (1.3% error compared with the simulation). Experienced rheological behavior of the liquid metal necessitates microfluidic channel modifications. For that reason, we modified the channel structure used to realise the radiating patch for the second design. Straight channels are implemented in the second microfluidic device. According to simulation the design yields a frequency tuning range of about 77% (i.e. 3.28 GHz) from 2.62 GHz to 5.90 GHz.

This paper presents the measurement results and analysis for outdoor wireless propagation channels at 26 GHz over 2 GHz bandwidth for two receiver antenna polarization modes. The angular and wideband properties of directional and virtually omni-directional channels, such as angular spread, root-mean-square delay spread and coherence bandwidth, are analyzed. The results indicate that the reflections can have a significant contribution in some realistic scenarios and increase the angular and delay spreads, and reduce the coherence bandwidth of the channel. The analysis in this paper also show that using a directional transmission can result in an almost frequencyflat fading channel over the measured 2 GHz bandwidth; which consequently has a major impact on the choice of system design choices such as beamforming and transmission numerology.

A novel dielectric resonator antenna (DRA) is presented for wideband circular polarization (CP). Two unequal inclined slits are loaded on the diagonal of the square DR to excite a CP mode. The effect of variation of ratio between the length of the slits on the CP and impedance characteristics is studied. The DR is excited by a proper tapered strip, connected to the input microstrip line from one side, and finally matched by a chip resistor from the lateral side. As the key parameters, the position of the excitation and matching lines and the impedance of the chip resistor are carefully optimized to adjust and improve the CP. The proposed configuration offers a relatively compact and easy-to-fabricate feeding network and multiresonant performance providing a 3-dB axial-ratio and impedance bandwidth of about (43-50)% around 3.7 GHz, gain between 4 and 6 dBi. The CP and impedance parameters of the antenna are studied, and reasonable agreement between the measured and simulated results is observed. © 2013 IEEE.

A novel coplanar waveguide-fed transparent antenna for ultrawideband applications with enhanced bandwidth is presented. In this design, different techniques have been used to broaden the bandwidth. The rectangular radiator of the antenna is equipped by the staircase technique to increase the overlapped resonant frequencies. Moreover, two major and minor symmetrical rectangular stubs are mounted on top of the quarter-circle slot ground by using a dual axis to significantly increase the bandwidth between 3.15 and 32 GHz for VSWR< 2. AghT-8 transparent thin film is used in the design of the proposed antenna to obtain a very compact size and lightweight structure. © 2014 IEEE.

A miniaturized V-band leaky-wave antenna (LWA) with circular polarization and backward-broadside-forward radiation based on a modified half-mode substrate integrated waveguide (M-HMSIW) is presented. The proposed M-HMSIW structure employs broadside coupled complementary split ring resonators to replace metallic vias, resulting in low-cost and fully-planar fabrication advantages over conventional HMSIWs. Each unit cell of the proposed LWA consists of an M-HMSIW in combination with two horizontal stubs and a cross-shaped complementary electric LC slot to provide a proper circular polarization with a composite right/left-handed property. Using this structure, the balanced condition can be obtained for the unit cell; hence a continuous backward-to-forward scanning, including broadside, is achieved. As a result, the proposed LWA with a radiator length of only 3.8 λ 0 provides wide-angle beam scanning from − 53° to + 54° over the frequency range of 61.2 GHz to 73.4 GHz, while maintaining an excellent circular polarization between − 25° and 25°. The maximum gain of the LWA is 11.1 dB which is satisfactory, considering its compactness. The antenna’s performance is experimentally verified, and close agreement between the simulations and measurements is observed.

The growing demands of advanced future communication technologies require investigating the possible enhancement in the current features of a reflectarray antenna. Its design and experimental features need a thorough investigation before a plausible transition towards millimeter wave frequencies. This article provides a detailed review covering various fundamental and advanced design tactics for polarization diversity and beamsteering in the reflectarray antenna. The diversity in the polarization has been discussed for linear and circular polarized designs in reflectarrays. The importance of electronically tunable materials and different lumped components for adaptive beamsteering in reflectarrays has also been highlighted. Each design has been critically analyzed and possibilities of its compatibility with future 5G systems have been provided.

A novel complex structure of Printed Dielectric Resonator Monopole Antenna (PDRMA) with multi-bands operation is presented and investigated. In the proposed structure, a printed fork-like stepped monopole antenna is used for exciting two new modified hemicylindrical dielectric resonators with a great relative permittivity of 80. A narrow medium substrate with a low permittivity is also applied between two mentioned dielectric resonators and the monopole antenna, to improve the matching, especially at the lower frequencies. By using this novel designed antenna applying two dielectric resonators with very high permittivity, many frequency wide bands for VSWR < 2 are practically measured and supported which are as follows: 1.54-3.25 GHz (GPS, GSM, PCS, UMTS 2000, 2.4 GHz-Bluetooth, WLAN, WiMax), 3.3-3.6 GHz (WiMax), 3.8-4.4 GHz (C-band), 4.8-6.2 GHz (5.2, 5.5 & 5.8 GHz-WLAN & WiMax). Experimental and numerical results are carried out and discussed, showing good agreement.

A triple-band planar monopole antenna is presented in this article. The antenna consists of three strips which correspond to operating frequency bands of 2.4, 3.5, and 5.8 GHz. The proposed antenna has been designed, simulated, and fabricated on 20 × 38 mm2 FR4 board. There is good agreement between simulation and measurement results in terms of return loss and radiation pattern. The proposed antenna provides measured -10 dB bandwidths of 200 MHz for the 2.4 GHz (from 2.36 to 2.56 GHz); 620 MHz for the 3.5 GHz (from 3.48 to 4.10 GHz); and 1.38 GHz for 5.8 GHz (from 5.65 to 7.03 GHz). Moreover, the antenna provides the measured gain of 4.73, 1.66, and 3.28 dBi for 2.4, 3.5, and 5.8 GHz, respectively. The radiation characteristics have proven that the proposed antenna seems to be a good potential candidate for WLAN/WiMAX applications. © 2013 Wiley Periodicals, Inc.

In order to solve the low signal-to-noise ratio (SNR) problem of the differential coincidence imaging (DCI) system, a frequency-diverse metacavity Cassegrain antenna (FDMCA) that is able to generate low-correlated bunching radiation patterns is proposed in this paper. The FDMCA is designed according to the Cassegrain antenna form, which consists of a frequency-diverse half-spherical metacavity etched with back-projecting slot arrays and a parabolic reflector. In total 81 useful measurement modes with a bunching angle of 40 ° are obtained from 32 to 36 GHz. Firstly, frequency-diverse field distributions in the metacavity are obtained utilizing a high-dispersion metasurface. Back-projecting slot arrays etched on the metacavity would couple the energy from the metacavity and back-radiate to the reflector. When placing the phase center of the feed source at the reflector focal point, the reflected patterns would be focused. Then, the performance of the proposed FDMCA is evaluated. In total 81 radiation patterns with correlation coefficients under 0.3 are generated. Finally, imaging experiments using the proposed FDMCA are carried out and the target image is reconstructed successfully using the DCI method. Comparative experiments are also implemented under the same conditions using a non-bunching frequency-diverse metasurface antenna to verify the bunching advantage of the FDMCA. The design is validated by simulations and measurements.

A polarisation insensitive transparent metasurface with two pass bands and two stop bands is proposed for 5G outdoor to indoor (O2I) coverage enhancement. Genetic Algorithm (GA) has been applied in order to provide the structural geometry of the unit cell for this metasurface. The proposed periodic structure consists of a unit cell design consisting of five stacked transparent patterned layers of Indium Tin Oxide (ITO) coated on Polyethylene Terephthalate (PET) substrates. The proposed transmission metasurface can be easily mounted on conventional glass windows to assist the O2I 4G/5G signals for the n7 and n78 of the 5G new radio (5G-NR), as well as shielding the 2.4/5 GHz WiFi signals from penetrating outside the building thereby enhancing the security.

This paper proposes a reconfigurable wideband artificial magnetic conductor (AMC), insensitive to the tilt-angle of linear polarization, that offers an overall AMC bandwidth of 550 MHz from 3.55 GHz to 4.1 GHz. The operating frequency of the proposed AMC can be altered by varying the reverse biasing of the varactor diodes. The proposed AMC is evaluated for variations in the tilt-angle of linear polarization and also as a reflector for a standard bowtie antenna due to its wideband characteristics. The results show its voltage-controlled wideband operation for obtaining a directional radiation pattern suitable for a typical wideband 5G base station antenna.

A novel P-shape wideband dielectric resonator antenna design is presented for wireless application in this paper. It is described by using a P-shape dielectric resonator with high dielectric constant (εr = 30) that is placed on the truncated ground plane, a wideband impedance bandwidth of about 64% (for VSWR≤2), covering the frequency range of 3.40-6.58GHz is achieved. Analysis of the proposed antenna is performed using CST Microwave Studio software. © 2010 IEEE.

An efficient terahertz (THz) photoconductive antenna (PCA) are proposed in this paper. The antenna is designed for continuous wave (CW) applications in the frequency range of 0.5-3 THz. The overall optical-to-THz efficiency of the proposed PCA is improved by enhancing the optical-to-electrical and radiation efficiencies. For the presented PCA, three types of excitation gap are investigated numerically and are compared. To enhance the excited photocurrent, plasmonic excitation is applied to amplify the electric field distribution in the structure. Owing to plasmonic excitation, the optical-to-electrical efficiency of photomixer is increased by a factor of 100. Moreover, the substrates of the proposed PCA is reshaped to improve the radiation efficiency, directivity and side lobe level (SLL). Finally, the radiation characteristics of the proposed PCA is compared with conventional extended-hemispherical lens antenna. The comparison shows a 4-fold reduction in size achieved by the proposed antenna compared to those with similar radiation features.

In this paper, we study an additional spatial diversity mechanism added to a cavity-backed frequency-diverse aperture for computational imaging applications at X-band frequencies. It is shown that the dynamic variation of cavity modes achieved by means of a simple, multi-port excitation mechanism can significantly simplify the diversity constraints on the frequency-diversity technique for computational imaging and can substantially improve the fidelity of the reconstructed microwave images. Leveraging the proposed technique, we present that, for the selected number of measurement modes, the condition number of the studied computational imaging problem is improved by 8.5 times in comparison to using the frequency-diversity as the only diversity mechanism. The reconstructed X-band images of various targets, including the letters “Q”, “U” and “B” reflect on this improvement and exhibit a higher reconstruction quality, significantly assisting in the identification of the imaged objects. We also present that the resolution limits of the frequency-diverse computational imaging system synthesized using the proposed multi-port cavity are in excellent agreement with the theoretical resolution limits.

In this work a circularly polarized linear parasitic DRs (Dielectric Resonators) antenna array for 5G applications is presented. The symmetrical linear array consists of five DR elements. The proposed configuration has a central driven element fed with coaxial probe. Two parasitic elements on each side of the driven element make the arrangement parasitic and symmetrical. All the DR elements including the driven and parasitic elements have the same relative permittivity (dielectric constant) with 0.5λ inter elements spacing. The driven element has a thin micro-strip line stacking for impedance matching. The linear array has reduced ground plane for wideband operations. The simulated wideband operations make the proposed design a good candidate for the 5G applications. The proposed design gives 100% impedance bandwidth and 69% circular polarization bandwidth. The performance parameters show that the proposed design is a good candidate for 5G applications.

In this paper, a low‐profile aperture‐stacked patch (LP‐ASP) antenna for breast cancer detection applications is proposed. The antenna is embodied by three substrate layers, in which one layer is applied to feed all stacks and the other two are adjoined substrates with rectangular patches, mounted on the top of the feeding layer. The feeding layer consists of a fork‐shaped strip on one side, and an H‐shaped slot attached to a cross‐shaped slot on the other side. By using the proposed feeding structure and a designed defected ground plane, an additional current path is provided which generates extra resonances and widens the impedance bandwidth from 2.5 to 15 GHz. The overall size of the antenna is 10 × 10 × 3.475 mm3, which is approximately 0.083λ × 0.083λ × 0.03λ at the antenna's lowest operating frequency. To evaluate the performance of the designed antenna in an imaging system, first, a breast model with an embedded spherical tumor (with a radius of 4 mm) is constructed. Then, a conformal array of the designed antenna with 17 elements on a cross‐arranged lattice is placed around the breast model. The quantitative metrics of the reconstructed images show that the proposed antenna can be a good candidate for the breast cancer detection applications.

This article investigates the feasibility of designing a high-gain on-chip antenna on silicon technology for sub-terahertz applications over a wide frequency range. High-gain is achieved by exciting the antenna using an aperture fed mechanism to couple electromagnetics energy from a metal slot-line, which is sandwiched between the silicon and polycarbonate substrates, to a 15-element array comprising circular and rectangular radiation patches fabricated on the top surface of the polycarbonate layer. An open ended microstrip line, which is orthogonal to the metal slot-line, is implemented on the underside of the silicon substrate. When the open ended microstrip line is excited it couples the signal to the metal slot-line which is subsequently coupled and radiated by the patch array. Measured results show the proposed on-chip antenna exhibits a reflection coefficient of less than -10 dB across 0.290 THz to 0.316 THz with a highest gain and radiation efficiency of 11.71 dBi and 70.8%, respectively, occurred at 0.3THz. The antenna has a narrow stopband between 0.292 THz to 0.294 THz. The physical size of the presented sub-terahertz on-chip antenna is 20×3.5×0.126mm3.

A millimeter-wave (mmW) classifier system applied to images synthesized from a coded-aperture based computational imaging (CI) radar is presented. A developed physical model of a CI system is used to generate the image dataset for the classification algorithm. A convolutional neural network (CNN) is integrated with the physical model and trained using the dataset comprising of synthesized mmW images obtained directly from the developed CI physical model. A k-fold cross validation technique is applied during the training process to validate the classification model. The coded-aperture CI concept enables image reconstruction from a significantly reduced number of back-scattered measurements by facilitating physical layer compression. This physical layer compression can substantially simplify the data acquisition layer of imaging radars, which is realized using only two channels in this article. The integration of the classification algorithm with the CI numerical model is particularly important in enabling the training step to be carried out using relevant system metrics and without the necessity for experimental data. Leveraging the CI numerical model generated data, training step for the classification algorithm is achieved in real-time while also confirming that the numerically trained CI classifier offers high accuracy with both simulated and experimental data. The classifier integrated physical model also enables performance analysis of the classification algorithm to be carried out as a function of key system metrics such as signal-to-noise (SNR) level, ensuring a complete understanding of the classification accuracy under different operating conditions. The trained CI system is tested with synthesized mmW images from the physical model and a classification accuracy of 89% is achieved. The proposed model is also verified using experimental data validating the fidelity of the developed CI integrated classifier system. A classification latency of 3.8 ms per frame is achieved, paving the way for real-time automated threat detection (ATD) for security-screening applications.

© 2015 EurAAP.The large bandwidth of ultra wideband (UWB) makes it attractive in high speed transmission applications. However, the possibility of frequency selectivity of the channel is high due to this bandwidth. Channel characterization is important to study the behavior of the channel. The ground reflection effects are important parameters affecting the ultra wideband channel. In this paper, based on outdoor time domain measurements, path loss model and root mean square (RMS) delay spread characteristics for near-ground (NG) UWB channel have been presented. Moreover, the interdependencies of these characteristics of the multipath channel are also investigated. The NG UWB channel characteristics are compared to the UWB channel above the ground. From the results it has been found that the path loss in NG UWB channel is less as compared to the above ground case. Also, the values of RMS delay spread are low.

Holographic Beamforming is a promising concept to reduce the power consumption of Multiple Input Multiple Output (MIMO) antenna arrays. In a holographic approach, the impedance of antenna patches is varied through the inclusion of tuning elements, such as varactor diodes, which allow electronic control of the phase and amplitude of each antenna. In this work, we provide the electromagnetic framework for the design of a Holographic MIMO Surface (HMIMOS). We analyze its performance and compare its power consumption to passive Reconfigurable Intelligent Surfaces (RIS) and MIMO Active Phased Arrays (APA) at 5G Frequency Range (FR) 2. The results show that the power consumption of HMIMOS is lower than of MIMO APAs, but significantly higher than of RISs. However, a combination of active and passive elements on a RIS can offer many benefits in terms of environmental awareness and intelligence for Integrated Sensing and Communication (ISAC) in Beyond 5G (B5G) networks.

A wideband multiple-input-multiple-output (MIMO) antenna system with common elements suitable for WiFi/2.4 GHz and Long Term Evolution (LTE)/2.6 GHz wireless access point (WAP) applications is presented. The proposed MIMO antenna system consists of four wideband microstrip feedline printed monopole antennas with common radiating element and a ring-shaped ground plane. The radiator of the MIMO antenna system is designed as the shape of a modified rectangle with a four-stepped line at the corners to enhance the impedance bandwidth. According to the common elements structure of the MIMO antenna system, isolation between the antennas (ports) can be challenging. Therefore, the ground plane is modified by introducing four slots in each corner to reduce the mutual coupling. For an antenna efficiency of more than 60%, the measured impedance bandwidth for reflection coefficients below -10 dB was observed to be 1100 MHz from 1.8 to 2.9 GHz. Measured isolation is achieved greater than 15 dB by using a modified ground plane. Also, a low envelope correlation coefficient (ECC) less than 0.1 and polarization diversity gain of about 10 dB with the orthogonal mode of linear polarization and quasi-omnidirectional pattern during the analysis of radiation characteristic are achieved. Therefore, the proposed design is a good candidate for indoor WiFi and LTE WAP applications due to the obtained results.

Beyond 5G networks would require newer technologies to deliver a smarter network. In accordance with these requirements, an electronically steerable compact antenna system capable of beam-switching in the azimuth plane is proposed. The design uses a monopole antenna as the main radiator surrounded by metasurface-based electronically reconfigurable reflector elements designed for the sub-6GHz range. The reflector elements use a reconfigurable capacitively loaded loop (CLL) which can be electronically activated to work as an artificial magnetic conductor (AMC). The design offers a digitally controllable directional radiation pattern covering all 360° in the azimuth plane with a step-size of 30°, a directional gain of ≥ 4.98 dBi and a high front-to-back lobe ratio (FBR) of ≥ 14.9 dB. The compact and modular nature of the design combined with the use of commercial off-the-shelf (COTS) components and 3D-printing makes the design low-cost and easier to integrate with various internet of thing (IoT) applications.

A coplanar waveguide (CPW) reconfigurable dielectric resonator antenna (DRA) is presented and investigated. The DRA is capable of frequency tuning at three different frequency bands between 3.45 and 6.77 GHz. The overall size of the antenna is 50 × 57 mm2. The dielectric material is a rectangular block of ceramic with a permittivity of 15. Two switches, implemented using p-i-n diodes, are located on the lines of a feed network that is connected to the dielectric element. Single-band modes with impedance bandwidths of 8% and 16% are achieved by switching 'on' one of three connecting feedline networks, whereas a wide band, with an impedance bandwidth of 65%, is achieved by switching 'on' two connecting lines. Frequencies in the single band can be independently controlled using switch positions without affecting the wideband mode. The prototype has a low profile with a dielectric resonator thickness of 4 mm. The characteristics of this antenna were studied, and good agreement was found between the numerical and measured results. © 2002-2011 IEEE.

A novel high-isolation, monostatic, circularly polarized (CP) simultaneous transmit and receive (STAR) array dielectric resonator antenna (DRA) is presented. The proposed in-band full-duplex (IBFD) CP DRA system consists of 32 identical elements for each transmit and receiver part. Each element includes two rectangular dielectric resonators with different permittivity of 5 and 10 excited by a vertical strip connected to the microstrip line at the backplane. A stub connected to the ground plane is added between Rx and Tx to improve the isolation. In addition, an inverted U-shaped parasitic strip is carefully placed between two feeding networks to further enhance the TX/RX isolation. The measured results exhibit high TX/RX isolation of more than 50 dB over the desired operating bandwidth from 4.8 GHz to 4.95 GHz with a high total efficiency greater than 85% and a peak gain of about 18.7 dBi for both Port 1 and Port 2.

In this paper, synthesis of the flat-top radiation pattern with sharp cutoff for reducing the lobing fades due to the presence of the earth is investigated. To this end, first the propagation factor is investigated. Then based on the propagation factor, the antenna pattern is examined at different levels of the cutoff to achieve a flat-top radiation with low level of lobing fades. Finally, synthesizing the desired radiation pattern is investigated through Woodward-Lawson method. Our studies reveal that that antenna with large length (> 12λ) provides the desired flat-top pattern with the appropriate cutoff. The aperture distribution of the desired pattern is provided and discussed.

The recent studies on hybrid beamformers with a combination of switches and phase shifters indicate that such methods can reduce the cost and power consumption of massive multiple-input multiple-output (MIMO) systems. However, most of the works have focused on the scenarios with frequency-flat channel models. This letter proposes an effective approach for such systems in frequency-selective channels and presents the closed-form expressions of the beamformer and the corresponding sum-rates. Compared to the traditional subconnected structures, our approach with a significantly smaller number of phase shifters results in a promising performance.

A new compact two-segments dielectric resonator antenna (TSDR) for ultrawideband (UWB) application is presented and studied. The design consists of a thin monopole printed antenna loaded with two dielectric resonators with different dielectric constant. By applying a combination of U-shaped feedline and modified TSDR, proper radiation characteristics are achieved. The proposed antenna provides an ultrawide impedance bandwidth, high radiation efficiency, and compact antenna with an overall size of 18 × 36 × 11 mm 3. From the measurement results, it is found that the realized dielectric resonator antenna with good radiation characteristics provides an ultrawide bandwidth of about 110%, covering a range from 3.14 to 10.9 GHz, which covers UWB application. © 2002-2011 IEEE.

This paper proposes a novel transmission policy for an intelligent reflecting surface (IRS) assisted wireless powered sensor network (WPSN). An IRS is deployed to enhance the performance of wireless energy transfer (WET) and wireless information transfer (WIT) by intelligently adjusting phase shifts of each reflecting elements. To achieve its self-sustainability, the IRS needs to collect energy from the ES to support its control circuit operation. Our proposed policy for the considered system is called IRS assisted harvest-then-transmit time switching (IRS-HTT-TS) which schedules the transmission time slots by switching between energy collection and energy reflection modes. We study the performance of the proposed transmission policy in terms of the achievable sum throughput, and investigate a joint design of the transmission time slots, the power allocation, as well as the discrete phase shifts of the WET and WIT. This formulates the problem as a mixed-integer non-linear program (MINLP), which is NP-hard and non-convex. To deal with this problem, we first relax it to the one with continuous phase shifts. Consequently, we propose a two-step approach and decompose the original problem into two sub-problem, each being solved separately. Specifically, we independently solve the first sub-problem with respect to the phase shifts of the WIT in terms of closed-form expression. Then, we consider two cases to solve the second sub- problem. For the special case without the circuit power of each sensor node, the Lagrange dual method and the Karush-Kuhn- Tucker (KKT) conditions are applied to derive the optimal closed- form transmission time slots, power allocation, and phase shift of the WET. Moreover, we exploit the second sub-problem for the general case with the circuit power of each sensor node, which can be solved via employing a semi-definite programming (SDP) relaxation.

The rectangular dielectric resonator antenna (RDRA) is presented to generate linearly polarized (LP) with omnidirectional radiation patterns. The proposed omnidirectional LP DRA is fed centrally by a coaxial probe and offers an impedance bandwidth of 130 MHz between 5.15 and 5.35 GHz for |S11| < -10 dB, which can be useful for 5.2-GHz WLAN applications. It is noted that by introducing several inclined slits to the diagonal and sidewalls of the RDR and also deducting a rectangular part of the top wall of the LP RDRA, degeneracy mode is excited to generate the circularly polarized (CP) fields. The proposed omnidirectional CP DRA with axial-ratio (AR) bandwidth of 210 MHz was designed for WLAN (5.15-5.35 GHz) applications. A parametric study is presented. The proposed CP DRA is built, and the characteristics of the antenna are measured. Very good agreement between numerical and measured results is obtained. © 2002-2011 IEEE.

In this paper, a high-gain phased array antenna with wide-angle beam-scanning capability is proposed for fifth- generation (5G) millimeter-wave applications. First, a novel, end-fire, dual-port antenna element with dual functionalities of radiator and power splitter is designed. The element is composed a substrate integrated cavity (SIC) and a dipole based on it. The resonant frequencies of the SIC and dipole can be independently tuned to broaden the impedance bandwidth. Based on this dual-port element, a 4-element subarray can be easily constructed without resorting to a complicated feeding network. The end-fire subarray features broad beam-width of over 180 degrees, high isolation, and low profile, rendering it suitable for wide-angle beam-scanning applications in the H-plane. In addition, the methods of steering the radiation pattern downwards or upwards in the E-plane are investigated. As a proof-of-concept, two phased array antennas each consisting of eight subarrays are designed and fabricated to achieve the broadside and wide-angle beam-scanning radiation. Thanks to the elimination of surface wave, the mutual coupling between the subarrays can be reduced for improving the scanning angle while suppressing the side-lobe level. The experimental predictions are validated by measurement results, showing that the beam of the antenna can be scanned up to 65 degrees with a scanning loss only 3.7 dB and grating lobe less than -15 dB.

In this paper, a novel terahertz (THz) spectroscopy technique and a new graphene-based sensor is proposed. The proposed sensor consists of a graphene-based metasurface (MS) that operates in reflection mode over a broad range of frequency band (0.2 -6 THz) and can detect relative permittivity of up to 4 with a resolution of 0.1 and a thickness ranging from 5 μm to 600 μm with a resolution of 0.5 μm. To the best of author’s knowledge, such a THz sensor with such capabilities has not been reported yet. Additionally, an equivalent circuit of the novel unit cell is derived and compared with two conventional grooved structures to showcase the superiority of the proposed unit cell. The proposed spectroscopy technique utilizes some unique spectral features of a broadband reflection wave including Accumulated Spectral power (ASP) and Averaged Group Delay (AGD), which are independent to resonance frequencies and can operate over a broad range of spectrum. ASP and AGD can be combined to analyse the magnitude and phase of the reflection diagram as a coherent technique for sensing purposes. This enables the capability to distinguish between different analytes with high precision which, to the best of author’s knowledge, has been accomplished for the first time.

This letter shows how slugs of liquid metal can be used to connect/disconnect large areas of metalization and achieve a radiation performance not possible by using conventional switches. The proposed antenna can switch its operating bandwidth between ultrawideband and narrowband by connecting/disconnecting the ground plane for the feedline from that of the radiator. This could be achieved by using conventional semiconductor switches. However, such switches provide point-like contacts. Consequently, there are gaps in electrical contact between the switches. Surface currents, flowing around these gaps, lead to significant back radiation. In this letter, the slugs of a liquid metal are used to completely fill the gaps. This significantly reduces the back radiation, increases the bore-sight gain, and produces a pattern identical to that of a conventional microstrip patch antenna. Specifically, the realized gain and total efficiency are increased by 2 dBi and 24%, respectively. The antenna has potential applications in wireless systems employing cognitive radio (CR) and spectrum aggregation.

In this paper, metamaterial loading on loop and open loop microstrip filters is investigated where both rectangular loop and open loop structures are considered. Spiral resonators are loaded on the four sides of the square loop and result in higher size reduction compared to the conventional split ring resonators with identical structural parameters. It is shown that, for both proposed filters, metamaterial loading provides size reduction, due to possessing lower resonant frequency of spiral resonators. The structures are analytically investigated through the transmission matrix method. In the designed rectangular loop filters, there are two nulls on both sides of the pass-band, which provide high out-of-band rejection and is preserved in the corresponding miniaturized metamaterial loaded structures. However open loop resonators provide lower resonant frequencies or more compact size filters. The proposed filter is fabricated and tested and measured results are in good agreement with simulation ones.

Simultaneous improvement of matching and isolation for a modified two-element microstrip patch antenna array is proposed. Two simple patch antennas in a linear array structure are designed, whereas, the impedance matching and isolation are improved without using any conventional matching networks. The presented low profile multifunctional via-less structure comprises of only two narrow T-shaped stubs connected to feed lines, a narrow rectangular stub between them, and a narrow rectangular slot on the ground plane. This design provides a simple, compact structure with low mutual coupling, low cost and no adverse effects on the radiation and resonance. To validate the design, a compact very-closely-spaced antenna array prototype is fabricated at 5.5 GHz which is suitable for multiple-input-multiple-output (MIMO) systems. The measured and simulated results are in good agreement with a 16 dB, and 40 dB of improvements in the matching and isolation, respectively.

© 2015 Wiley Periodicals, Inc.A multiple input multiple output (MIMO) F-shaped dielectric resonator antenna (DRA) for mobile device is presented in this article. The F-shaped DRA is mounted on FR4 as a substrate. The measured impedance bandwidth for Port 1 is 36% (2.30-3.31 GHz) while Port 2 is 31% (2.30-3.14 GHz), respectively with isolation of -33 dB. Two orthognal modes are excited in this design which are TE1δ1y mode at Port1 and TEδ11x at Port 2. Correlation coefficient of a MIMO F-shaped DRA is 0.04 with diversity gain nearly 10 dB over operating frequency. The antenna provides gain 1.99 dBi for Port 1 and 1.85 dBi for Port 2 at frequency 2.6 GHz. The parameters, isolation, gain, correlation coefficient, and diversity gain of the MIMO rectangular dielectric resonator antenna are studied, and reasonable agreement between the measured and simulated results is observed.

Proof-of-concept is presented of a novel slot antenna structure with two excitation ports. Although this antenna provides a wide impedance bandwidth, its peak gain and optimum radiation efficiency are observed at its mid-band operational frequency. The antenna structure is etched on the top side of a dielectric substrate with a ground plane. The antenna essentially consists of a rectangular patch with two dielectric slots in which multiple coupled patch arms embedded with H-shaped slits are loaded. The two dielectric slots are isolated from each other with a large H-shaped slit. The radiation characteristics of the proposed antenna in terms of impedance bandwidth, gain and efficiency can be significantly improved by simply increasing the number of radiation arms and modifying their dimensions. The antenna's performance was verified by building and testing three prototype antennas. The final optimized antenna exhibits a fractional bandwidth of 171% (0.5-6.4 GHz) with a peak gain and maximum radiation efficiency of 5.3 dBi and 75% at 4.4 GHz, respectively. The antenna has physical dimensions of 27×37×1.6 mm3 corresponding to electrical size of 0.0452λ0×0.0627λ0×0.0026λ0, where λ0 is free-space wavelength at 0.5 GHz. The antenna is compatible for integration in handsets and other broadband wireless systems that operate over L-, S-, and C-bands.

This paper introduces a millimeter-wave multipleinput- multiple-output (MIMO) antenna for autonomous (selfdriving) cars. The antenna is a modified four-port balanced antipodal Vivaldi which produces four directional beams and provides pattern diversity to cover 90 deg angle of view. By using four antennas of this kind on four corners of the car’s bumper, it is possible to have a full 360 deg view around the car. The designed antenna is simulated by two commercially full-wave packages and the results indicate that the proposed method can successfully bring the required 90 deg angle of view.

This paper presents a brief account of the findings on a switched parasitic dielectric resonator antenna (DRA) array excited in a higher-order mode. The scanning phase can be changed by using switching technique and capacitor loading at the parasitic element. The driven DR and parasitic DRs have a dielectric constant of 10 and were fed by a microstrip slot aperture. The impact of mutual coupling on the reflection coefficient was examined through a numerical calculation which combines both ANSYS HFSS and MATLAB. This phased array was shown to be able to steer the antenna beam from −26 degrees to +26 degrees at 15 GHz, which is considered suitable for 5G applications. The impedance matching was maintained at all beam steering angles and a bandwidth of 2.6 GHz has been achieved.

Traditional design of 4 x 4 Butler matrix (BM) uses couplers, phase shifters (PS) and crossovers. Due to some troublesome issues related to PS and the crossovers involved in the design of BM which degrades its performance, this paper presents a planar 4 x 4 BM without PS and crossovers. It is accomplished with the help of a modified coupler. The modified coupler is realized to have a 450 output phase difference which replaces the function of the 450 phase shifters. The 450 output phase differences obtained from this type of coupler combined with quadrature coupler gives the desired phase differences required at the output of the BM. The BM is meant to operate at 6 GHz. The simulated and measured reflection coefficients and isolations at all ports are below −17 dB at the center frequency. The result also shows an amplitude imbalance within ±3 dB with phase mismatch of about ±3° at the center frequency. The −10 dB reflection coefficient bandwidth is 37.10% and the transmission bandwidth between −5 dB and −9 dB is about 31.0%. Both the simulated and experimental radiation patterns obtained by exciting the input ports (P1 to P4) of the BM produces four orthogonal beams deposed at +15.3°, −47.6°, +47.6° and −15.3°. This beam steering depicts a stable beam scanning angle of the BM which is in good agreement with the theoretical predictions.

A machine learning (ML) technique has been used to synthesis a linear millimetre wave (mmWave) phased array antenna by considering the phase-only synthesis approach. For the first time, gradient boosting tree (GBT) is applied to estimate the phase values of a 16-element array antenna to generate different far-field radiation patterns. GBT predicts phases while the amplitude values have been equally set to generate different beam patterns for various 5G mmWave transmission scenarios such as multicast, unicast, broadcast and unmanned aerial vehicle (UAV) applications.

In this paper, a single-layer planar antenna with vertical polarization and omni-directional radiation is proposed for wearable applications. The antenna consists of two identical shorted patches which are face-to-face located and fed by a microstrip line at the center. Due to the structural symmetry, the current distribution and electric-field distribution are symmetrical regarding the feed, which result in vertical linear polarization normal to the antenna and omni-directional radiation pattern in the azimuthal plane. To verify the design concept, an antenna prototype operating at 2.45 GHz is designed, fabricated and tested. Measured results concur well with the simulations, showing that the antenna has a good impedance matching, omnidirectional radiation pattern, and vertical polarization in the band of interest. The proposed antenna can be a good candidate for wearable and other wireless communication systems.

In this paper, an ultra-wideband, Dielectric Resonator Antenna (DRA) has been proposed. The proposed antenna is based on isosceles triangular DRA (TDRA), which is fed from the base side using a 50Ω probe. For bandwidth enhancement and radiation characteristics improvement, a partially cylindrical-shape hole is etched from its base side which approached probe feed to the center of TDRA. The dielectric resonator (DR) is located over an extended conducting ground plane. This technique has significantly enhanced antennas bandwidth from 48.8% to 80% (5.29-12.35 GHz), while the biggest problem was radiation characteristics. The basis antenna possesses negative gain in a wide range of bandwidth from 7.5 GHz to 10.5 GHz down to -13.8 dBi. Using this technique improve antenna gain over 1.6 dBi for whole bandwidth, while peak gain is 7.2 dBi.

This paper presents a framework for achieving machine learning (ML)‐assisted direction‐of‐arrival (DoA) accuracy enhancement using a millimetre‐wave (mmWave) dynamic aperture. The technique used for the enhanced DoA estimation accuracy leverages an over‐sized lens‐loaded cavity antenna connected to a single RF chain in the physical layer and a computational method in the computational layer of the framework. It is shown for the first time that by introducing a reconfigurable mode‐mixing mechanism inside the over‐sized lens‐loaded cavity hardware, a greater number of spatially orthogonal radiation modes can be achieved giving rise to many cavity states. If the best cavity state is determined and selected by means of design exploration using a contemporary ML‐assisted antenna optimisation method, the computational DoA estimation accuracy can be improved. The mode‐mixing mechanism in this work is a randomly oriented metallic scatterer located inside an over‐sized constant−ϵr lens‐loaded cavity, connected to a stepper motor that is electronically controlled by inputs from the computational layer of the presented framework. Measurement results in terms of near‐field radiation mode scans are included in this study to verify and validate that the proposed ML‐assisted framework enhances the DoA estimation accuracy. Moreover, this investigation simultaneously provides a simplification in the physical layer implementation of mmWave radio hardware, and DoA accuracy enhancement, which in turn lends itself favourably to the adoption of the proposed framework for channel sounding in mmWave communication systems.

Conference Title: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/USNC-URSI) Conference Start Date: 2022, July 10 Conference End Date: 2022, July 15 Conference Location: Denver, CO, USAA wide-incident angle and polarisation insensitive transparent metasurface is presented for 5G outdoor to indoor coverage enhancement. In order to predict the structural geometry of the unit cell, the Genetic Algorithm (GA) has been applied. The proposed unit cell is arranged in a periodic structure to construct the transmission surface consisting of tow transparent layers of Indium Tin Oxide (ITO) mounted on both sides of Polyethylene Terephthalate (PET) substrate. The proposed transmission metasurface can be simply coated on a glassy windows to empower the outdoor to indoor 5G signals.

This paper proposes an ultra-compact Near-field Focusing (NFF) setup at 60 GHz. The proposed configuration is included a planar substrate integrated waveguide (SIW) slot array as a feeder for a three-layer transmissive coded metasurface lens. A comprehensive design methodology is presented, encompassing unit cell design, coded metasurface lens synthesis, and planar slot array design. The transmissive metasurface lens performance is studied and validated by numerical and analytical approaches. Then, the planar slot array design considerations are elaborated, investigating the amplitude and phase of the resulting waves to ensure that quasi-plane waves are produced in the near-field region. Finally, the slot array is employed to illuminate the designed metasurface where the distance between the feeder and metasurface lens is 2 mm (0.4λ), which shows the integrability and being packed of the proposed setup, contrary to the conventional metasurface-based NFF structures. There are fair agreements between analytical, numerical, and measurement methods to verify the presented approach. It turns out that the proposed device can focus waves close to the diffraction limit, which results in a high-resolution efficiency.

© 2014 IEEE.In this paper a compact dual-port Multiple Input Multiple Output (MIMO) Dielectric Resonator Antenna (DRA) with high isolation has been presented and discussed. The DR is fed by two probe feeds, one touching the side wall of the DR while the other is drilled in the middle of the DR. Both the ports are excited in orthogonal modes with the same resonance frequency in the DR, thus resulting in high isolation. The presented antenna is suitable to operate at LTE bands 7 and 38. The bandwidth achieved is 310 MHz and an isolation of +15 dB has been obtained. Besides, the Envelop Correlation Coefficient (ECC), and Diversity Gain (DG) has also been studied for the proposed antenna.

Here, we first aim to explain practical considerations to design and implement a reconfigurable intelligent surface (RIS) in the sub-6 GHz band and then, to demonstrate its real-world performance. The wave manipulation procedure is explored with a discussion on relevant electromagnetic (EM) concepts and backgrounds. Based on that, the RIS is designed and fabricated to operate at the center frequency of 3.5 GHz. The surface is composed of 2430 unit cells where the engineered reflecting response is obtained by governing the microscopic characteristics of the conductive patches printed on each unit cell. To achieve this goal, the patches are not only geometrically customized to properly reflect the local waves, but also are equipped with specific varactor diodes to be able to reconfigure their response when it is required. An equivalent circuit model is presented to analytically evaluate the unit cell’s performance with a method to measure the unit cell’s characteristics from the macroscopic response of the RIS. The patches are printed on six standard-size substrates which then placed together to make a relatively big aperture with approximate planar dimensions of 120 W 120 cm2. The manufactured RIS possesses a control unit with a custom-built system that can control the response of the reflecting surface by regulating the performance of the varactor diode on each printed patch across the structure. Furthermore, with an introduction of our test-bed system, the functionality of the developed RIS in an indoor real-world scenario is assessed. Finally, we showcase the capability of the RIS in hand to reconfigure itself in order to anomalously reflect the incoming EM waves toward the direction of interest in which a receiver could be experiencing poor coverage.

In this paper, a new method is proposed to reduce mutual coupling between waveguide slot array (WSA) antennas based on metasurface technology. This is achieved by placing a metasurface bulkhead between the two WSA antennas. Performance of the dual-waveguide antenna structure is shown to substantially enhance when compared against an identical reference WSA antenna with no metasurface. WSA antennas used in the study has dimensions 40×20×5mm3 and operates over 1.7-3.66 GHz, which corresponds to a fractional bandwidth of 73.13%. The average isolation of the reference WSA antennas is -20 dB; however, with a metasurface bulkhead the isolation is shown to increase to -36.5 dB. In addition, the bandwidth extends by ~10%, and the gain improves by 14.66%. The proposed method is should find application in MIMO systems where high isolation between neighbouring radiation elements is required to improve the antenna characteristics, and mimimise array phase errors, which is necessary to enhance the system performance.

A reconfigurable metamaterial-inspired unit cell is proposed that can be reconfigured to behave either as a perfect magnetic conductor (PMC) or as a perfect electric conductor (PEC) and its application to waveguide miniaturisation is demonstrated. The unit cell is designed to operate in the sub-6 GHz band at 3:6 GHz with a PMC bandwidth of 150 MHz and has a simple construction that makes the design easy to fabricate. The phase response of the reconfigurable unit cell is presented and a prototype design of a miniaturised waveguide using the proposed unit cell is also proposed. The performance and field distribution of the waveguide are analysed which demonstrate the existence of a pass-band spanning 160 MHz below the cutoff frequency and the presence of a quasi TEM mode.

An ultra wideband printed monopole antenna with dual band circular polarization for wireless application is presented. The antenna dimensions are 30 × 30 × 1.6 mm3. The proposed antenna is able to cover frequency range between 2.65 GHz and 11GHz with impedance bandwidth is around 122%. With the use of I-shape slit in the radiation element and the T-slot in the ground plane, the ultra wideband and circular polarization are excited. In addition, the rectangular slit is added in the ground plane, to enhance the impedance- and Axial Ratio - bandwidth. Furthermore, the dual band circular polarization with right hand circular polarization at 3.1 GHz and the left hand circular polarization at 7GHz are obtained. Also, the 3-dB axial ratio bandwidths are about 242 and 246 MHZ at the lower and upper band without rectangular slit and 356 and 546 MHZ at the lower and upper band with rectangular slit, respectively. © 2011 EurAAP.

This paper presents details of the indoor wideband and directional propagation measurements at 26 GHz in which a wideband channel sounder using a millimeter wave (mmWave) signal analyzer and vector signal generator was employed. The setup provided 2 GHz bandwidth and the mechanically steerable directional lens antenna with 5 degrees beamwidth provides 5 degrees of directional resolution over the azimuth. Measurements provide path loss, delay and spatial spread of the channel. Angular and delay dispersion are presented for line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios.

A P-shaped monopole antenna (PSMA) attached with a glass substrate is proposed for wireless body area networks (WBAN) applications. The study investigates the performance of PSMA above reflection plane substrates with different material of glass and a perfect electric conductor (PEC). The PSMA prototype is fabricated on the FR4 substrateto be operated between 3.1 to 5.1 GHz frequency band. It is discovered that the PSMA efficiency could be enhanced by integrating the ground plane with a glass for the brain and chest human body. For brain model, the antenna efficiency of 78.8%, 80.3% and 85.6% is achieved for 3.3, 4.45 and 5 GHz respectively. The antenna efficiency in the chest model is improved to 75.2%, 76.35% and 81.2% at particular 3.3, 4.45 and 5 GHz respectively. Therefore, this study concludes that the reflection plane help to increase the gain and efficiency of close proximity of body surface. Additionally, the PSMA with reflection plane improves SAR when placed near human body if compared to the other antennas. A fascinating conformity was found between the simulation and measurement results that potentialto be deployed for WBAN applications.

In this paper, a high flat gain waveguide-fed aperture antenna has been proposed. For this purpose, two layers of FR4 dielectric as superstrates have been located in front of the aperture to enhance the bandwidth and the gain of the antenna. Moreover, a conductive shield, which is connected to the edges of the ground plane and surrounding aperture and superstrates, applied to the proposed structure to improve its radiation characteristics. The proposed antenna has been simulated with HFSS and optimized with parametric study and the following results have been obtained. The maximum gain of 13.0 dBi and 0.5-dBi gain bandwidth of 25.9 % (8.96 – 11.63 GHz) has been achieved. The 3-dBi gain bandwidth of the proposed antenna is 40.7% (8.07-12.20 GHz), which has a suitable reflection coefficient (≤-10dBi) in whole bandwidth. This antenna comprises a compact size of (1.5λ×1.5λ), easy structure and low-cost fabrication.

© 2015, Penerbit UTM Press. All rights reserved.Design of a Dual-Band Dielectric Resonator Antenna (DRA) for the radio-frequency identification (RFID) and wireless local area network (WLAN) is presented. The necessity of a compact sized dual-band antenna is to allow the manufacturers to produce small size high-performance WLAN access points. The proposed antenna consists of printed TShaped monopole antenna and rectangular dielectric resonator to operate simultaneously at 2.4 and 5.8 GHz. The monopole antenna was printed on a standard 1.6 mm FR4 substrate material. Impedance bandwidth for -10 dB return loss in the 2.35 GHz and 5.86 GHz center frequency reaches 0.25 GHz (2.22 GHz to 2.47 GHz) and 0.28 GHz (5.72 GHz to 6 GHz), respectively. A good agreement is achieved between measured and simulated results. This compact antenna fed by a 50 O microstrip line is a low-profile and easy to manufacture antenna.

A low complexity massive multiple-input multipleoutput (MIMO) technique is studied with a geometry-based stochastic channel model, called COST 2100 model. We propose to exploit the discrete-time Fourier transform of the antenna correlation function to perform user scheduling. The proposed algorithm relies on a trade off between the number of occupied bins of the eigenvalue spectrum of the channel covariance matrix for each user and spectral overlap among the selected users. We next show that linear precoding design can be performed based only on the channel correlation matrix. The proposed scheme exploits the angular bins of the eigenvalue spectrum of the channel covariance matrix to build up an “approximate eigenchannels” for the users. We investigate the reduction of average system throughput with no channel state information at the transmitter (CSIT). Analysis and numerical results show that while the throughput slightly decreases due to the absence of CSIT, the complexity of the system is reduced significantly.

A printed spiral resonator without external lumped elements is proposed. Instead of employing surface-mount device (SMD) capacitors, series-parallel capacitive plates are designed and etched on the same substrate to achieve simultaneous conjugate matching between a pair of symmetrical near-field coupled resonators. Simulations are conducted with the aid from CST Microwave Studio. The proposed design displayed satisfactory tolerance towards planar displacement at z-axis plane, lateral displacement at x- and y-axis planes as well as concurrent planar and lateral displacement. Positioned at perfect alignment with a transfer distance of 15 mm, the simulated and measured maximum power transfer efficiency achieved are 79.54% and 74.96% respectively. The variation ratio for planar displacement acquired is 0.29% when receiving resonator is rotated from -180º till 180º with step size of 15º. Under rotational angle from 0º till 180º, the measured average variation ratio for lateral displacement at x- and yaxis up to 15 mm is 20.14%. Feasibility of sustaining power transfer efficiency under various offsets depicts the possibility of integrating the proposed simple design for low power wireless energy transfer applications such as wireless charging for handheld devices in consumer electronics and implanted biomedical devices.

The design and analysis of reconfigurable meta-surfaces operating within rich multi-path propagation fading is of crucial importance for the development of real-life programmable electromagnetic environments. We incorporate the effect of multi-path fading in an impedance-based model of wireless communication links assisted by reconfigurable surfaces. Previous work has shown that impedance-based channel models under rich multi-path propagation have an isomorphism with Sherrington-Kirkpatrick (SK) Hamiltonians. We focus on received power minimisation, which is equivalent to the hard-to-solve task task of finding the ground state of the SK Hamiltonian. It has been recently discovered that the Quantum Approximate Optimisation Algorithm (QAOA) predicts the ground state of SK Hamiltonians accurately. However, the landscape parameters of QAOA are dependent on the specific realisation of the random SK Hamiltonian, which hinders the full usage of quantum hardware to optimise reconfigurable surfaces dynamically. We show by Montecarlo simulations that a concentration property cures this impediment thus making QAOA an excellent candidate for surface optimisation under fast multi-path fading.

This paper highlights the crucial importance of polarization control within 5G wireless communication. We propose a compact polarization converter on a thin ferrite-based metasurface, which enables flexible manipulation of polarization in the reflected waves. The direction of applied magnetics bias allows the metasurface to polarize reflected waves in either co-or cross-polarization with respect to the incident wave. To optimize ferrite utilization, the adoption of a cubic lattice structure in metasurface design is recommended. This design approach has successfully delivered efficient polarization conversion and showcased impressive frequency reconfigurability. Each unit cell within the proposed metasurface can be independently controlled for spatial modulation. Utilizing the distinct material properties associated with various polarizations, the suggested metasurface exhibits remarkable potential in creating reflective intelligent surfaces. These surfaces have the capacity to substantially enhance coverage and elevate the performance of 5G networks. Index Terms—Ferrite, metasurface, polarization control, 5G, non-reciprocal wave propagation, Faraday rotation. I. INTRODUCTION As the demand for high-speed, low-latency, and reliable wireless communication continues to surge, the development of advanced technologies to enhance 5G networks becomes dominant. Metasurfaces in 5G applications enable precise beamforming and enhance wireless communication efficiency, revolutionizing the way data is transmitted and received, thus shaping the future of high-speed connectivity [1]–[3]. In this context, the manipulation of electromagnetic wave polarization has emerged as a crucial factor for improving the performance and efficiency of communication systems. Polarization converters, which can transform incident waves into desired polarizations, have garnered significant attention [4], [5]. This paper considers solutions in the form of a compact polarization converter, engineered on a thin ferrite-based metasurface, that holds great potential for revolutionizing 5G wireless communication. In previous investigations, various geometries have been investigated for achieving linear-to-cross polarization conversion , such as H-shaped metallic structures [6], the double-split ring resonator [7], and double V-shaped resonators [8]. Additionally, the effective realization of linear-to-circular polarization conversion has been demonstrated through designs like the Jerusalem Cross resonator and corner-truncated patch resonator [9]. Notably, a reconfigurable metasurface,

A Dual band rectangular dielectric resonator antenna (RDRA) capable of frequency tunings at two different resonant modes is presented and investigated. In this design two rectangular dielectric resonators with different permittivity situated on top of the substrate are employed. The antenna is fed by 50Ω microstrip feedline etched on the top of the Fr-4 epoxy printed circuit board (PCB) with a total size of 80 × 50 × 1.6mm3 and εrs = 4.6 (loss tangent = 0.02). In order to excite two resenant frequencies, two RDRA with relative permittivity of εr1 = 10 and εr2 = 30 are chosen to operate at 2.4 GHz and 3.8 GHz. From the parametric study the lower permitivity DRA resonates at 3.8 GHz whereas the higher permitivity DRA resonates at 2.4 GHz. Ansoft HFSS v14 has been used for the simulation of the proposed dual-band antenna. The simulation results show that the 3.8 design can efficiently perform in both frequency bands.

his paper presents a new dual and complementaryimpedance metasurface platform for studying Line Waves (LWs), electromagnetic modes at interfaces of different metasurfaces like capacitive and inductive types. The excited states, characterized by efficient one-dimensional propagation and tight interface confinement, hold promise for robust waveguide applications, especially within fifth-generation (5G) technology. The research shows that LW, supporting broadband frequencies, can be tuned through capacitive or inductive properties, with a semi-analytical model developed for in-depth analysis. Additionally, a parallel plate waveguide composed of four metasurfaces demonstrates LW robust transmission capabilities, even under longitudinal warping. This highlights their potential in wearable wireless communications and flexible electronics, showcasing their adaptability and efficiency.

—In this paper, a multi-hop reconfigurable intelligent surfaces (RIS) aided multiple-input single-output (MISO) system is studied to mitigate significant channel attenuation in Millimeter wave and terahertz communication. The achievable sum rate of the system is maximized via optimizing the passive elements at the RISs with an iterative algorithm. Simulation results imply that the proposed algorithm is able to improve the achievable sum rate by increasing the number of RISs.

—This paper presents a unit cell with high efficiency for simultaneous transmission and reflection (STAR) surface operating at millimeter wave frequencies. Applying two perpendicular metallic gratings in the top and bottom of a dual-C shaped resonator, the unit cells can simultaneously control amplitude and phase of reflected and transmitted waves by adjusting the geometrical parameters. This structure can be leveraged to realize full-space electromagnetic manipulation in a simple way for potential applications in mutlifunctional devices.

A simultaneously transmitting and reflecting surface (STARS) enabled integrated sensing and communications (ISAC) framework is proposed, where a novel bi-directional sensing-STARS architecture is devised to facilitate the full-space communication and sensing. Based on the proposed framework, a joint optimization problem is formulated, where the Cramér-Rao bound (CRB) for estimating the 2-dimension direction-of-arrival of the sensing target is minimized. An alternating optimization algorithm is proposed. In particular, the maximum number of deployable sensors is obtained in the closed-form expressions. Simulation results validate that: 1) STARS was capable of providing superior sensing performance compared to the conventional reconfigurable intelligent surface, and 2) the maximum likelihood estimator can be adopted in the proposed strategy to achieve high-quality sensing.

© 2014 Institute of Antenna Engineers of Taiwan.A dielectric resonator based metamaterial antenna is presented for dual band operations. The hybrid design uses the dielectric resonator (DR) and split ring resonator (SRR) to radiate two resonant modes. The antenna has a compact size of 40 × 40 mm2. The peak realized gain of 6.24 dBi and 6.04 dBi is obtained at 5.5 GHz and 5.8 GHz respectively. Also a peak efficiency of 94% is obtained across the covering frequency. The antenna has potential applications for WiMAX (5.5 GHz) and WLAN (5.8 GHz) operations.

By performing the Floquet-mode analysis of a periodic slotted waveguide, a multiple-beam leaky wave antenna is proposed in the millimetre-wave (mmW) band. Considering the direction of surface current lines on the broad/side-walls of the waveguide, the polarization of constructed beams are also controlled. The simulation results are well matched with the initial mathematical analysis.

This paper proposes a low-complexity hybrid beamforming design for multi-antenna communication systems. The hybrid beamformer comprises of a baseband digital beamformer and a constant modulus analog beamformer in radio frequency (RF) part of the system. As in Singular-Value-Decomposition (SVD) based beamforming, hybrid beamforming design aims to generate parallel data streams in multi-antenna systems, however, due to the constant modulus constraint of the analog beamformer, the problem cannot be solved, similarly. To address this problem, mathematical expressions of the parallel data streams are derived in this paper and desired and interfering signals are specified per stream. The analog beamformers are designed by maximizing the power of desired signal while minimizing the sum-power of interfering signals. Finally, digital beamformers are derived through defining the equivalent channel observed by the transmitter/receiver. Regardless of the number of the antennas or type of channel, the proposed approach can be applied to wide range of MIMO systems with hybrid structure wherein the number of the antennas is more than the number of the RF chains. In particular, the proposed algorithm is verified for sparse channels that emulate mm-wave transmission as well as rich scattering environments. In order to validate the optimality, the results are compared with those of the state-of-the-art and it is demonstrated that the performance of the proposed method outperforms state-of-the-art techniques, regardless of type of the channel and/or system configuration.

A frequency tunable dielectric resonator antenna (DRA) is studied and presented for ISM and LTE band applications. Here, the frequency operation of the proposed DRA is switched from dual band to narrowband mode by using the PIN diode switches. The switches are employed by RF PIN diodes and placed on the feed line network to excite the dielectric resonator (DR). The proposed reconfigurable DRA has a compact size with a thickness of 3 mm and the overall size of 30 × 37 mm2 that is proper for mobile devices. The measured and simulated results indicate that the proposed DRA provides a single and dual band modes which covers the ISM applications and 2.6 GHz LTE system, respectively.

In this paper, a design approach for aperture coupled modified cylindrical dielectric resonator antenna (cDRA) array is discussed. The proposed radiating element is dual cylindrical ceramic blocks placed with a small gap. The proposed aperture excites dual radiating mode pattern inside modified cDRA, i.e., HEM11δ and TE01δ . The arrangement of radiating elements, i.e., dual cylindrical ceramic blocks, provides lower Q -factor (wider impedance bandwidth). Conversion from a single radiating element to an array arrangement provides the gain enhancement of 3.0 dBi in the complete operating frequency range. The proposed aperture offers circularly rotating EM wave within frequency range 4.5–5.7 GHz. Antenna prototype is fabricated for the validation of simulated near as well as far-field parameters. Practically measured outcomes confirm that it is working in between the frequency range 4.7–6.4 GHz. The 3-dB axial ratio bandwidth of the proposed radiator is about 23.52% (4.5–5.7 GHz). Directional radiation pattern and circular polarization features make the proposed radiating structure more appropriate for WLAN (5.2 GHz) and local thermal equilibrium (LTE) band 46 (5.5 GHz) applications.

This paper presents a machine learning (ML) based model to predict the diffraction loss around the human body. Practically, it is not reasonable to measure the diffraction loss changes for all possible body rotation angles, builds and line of sight (LoS) elevation angles. A diffraction loss variation prediction model based on a non-parametric learning technique called Gaussian process (GP) is introduced. Analysed results state that 86% correlation and normalised mean square error (NMSE) of 0.3 on the test data is achieved using only 40% of measured data. This allows a 60% reduction in required measurements in order to achieve a well-fitted ML loss prediction model. It also confirms the model generalizability for non-measured rotation angles.

Surface electromagnetics (SEM), as a sub-discipline of electromagnetic (EM) science, is strongly linked with the ability to manipulate an arbitrary EM wavefront. This exceptional capability of manipulating the surface-bound and free-space EM waves for the guidance and control of anomalous reflection, refraction and transmission has catapulted an abundance of new research frontiers. This has resulted in the realization of many novel applications for modern real-life platforms and the introduction of several new modelling techniques and engineering approaches to give rise to some unconventional devices. Consequently, EM engineered metasurfaces, due to numerous emerging applications, are beginning to revolutionize the EM industry. Recently, the practical usage of metasurfaces has gained a substantial amount of interest and traction for a wide range of applications in microwave, millimetre-wave (mmWave), Terahertz (THz) and even optical wavelengths. This tutorial is aimed at presenting a plethora of EM metasurface applications and research frontiers to illustrate a broader impact of SEM in real-world platforms, advanced communication systems and new devices.

—A wide-incident angle and polarisation insensitive transparent metasurface is presented for 5G outdoor to indoor coverage enhancement. In order to predict the structural geometry of the unit cell, the Genetic Algorithm (GA) has been applied. The proposed unit cell is arranged in a periodic structure to construct the transmission surface consisting of tow transparent layers of Indium Tin Oxide (ITO) mounted on both sides of Polyethylene Terephthalate (PET) substrate. The proposed transmission metasurface can be simply coated on a glassy windows to empower the outdoor to indoor 5G signals.

—A dual-polarized dielectric resonator antenna (DRA) is investigated and discussed. The probe and microstrip feed line excite linear polarization (LP) and broadside circular polarization (CP), respectively. These different radiation patterns are obtained 43 % overlapping bandwidth. The measured results show that the antenna provides 43 % bandwidth, excited by probe feed line that produces linearly polarized and 74 % impedance bandwidth using microstrip feed line with the 18 % circularly polarized. The total overlapping bandwidth is 43 % starting from 8.65 GHz to 13.44 GHz. The antenna gain is between 3.4 and 5.2 dBi for linear polarized and between 2.8 and 5.1 dBi for circularly polarized patterns in the whole covered range.

This paper presents empirically based ultrawideband and directional channel measurements, performed in the Terahertz (THz) frequency range over 250 GHz bandwidth from 500 GHz to 750 GHz. Measurement setup calibration technique is presented for free-space measurements taken at Line-of-Sight (LoS) between the transmitter (Tx) and receiver(Rx) in an indoor environment. The atmospheric effects on signal propagation in terms of molecular absorption by oxygen and water molecules are calculated and normalized. Channel impulse responses (CIRs) are acquired for the LoS scenario for different antenna separation distances. From the CIRs the Power Delay Profile (PDP) is presented where multiple delay taps can be observed caused due to group delay products and reflections from the measurement bench.

A wideband frequency reconfigurable dielectric resonator antenna (DRA) is presented and discussed. The proposed antenna is capable of frequency switching at two different bands between 4.12 GHz and 8.85 GHz. The rectangular dielectric resonator with a permittivity of 15 is fed by U-shaped microstrip feed line. By setting the switch on the connecting lines of a network that feeds the dielectric element and changing the state of switch from ON to OFF, a shift of the well-matched operating frequency range is obtained. The total antenna dimensions are 40 × 45 × 4.5748 mm3. The results indicate that the proposed antenna with acceptable performance provides two wideband modes with the impedance bandwidth of 49% and 25%.

In this work, a dielectric resonator antenna (DRA) is miniaturized by using Artificial Magnetic conductor (AMC) surface without disturbing other important parameters. The design has three main features: (i) simple micro-strip line feeding, (ii) use of parasitic metallic strip to achieve impedance matching, and (iii) use of AMC surface for design miniaturization. The miniaturization is performed for dielectric resonator antenna at 3.5 GHz. Without changing the basic characteristic of the antenna such as gain, resonance frequency and efficiency, the size of the antenna was reduced by 85%. The AMC surface and DRA both are positioned on the FR4 substrate. The AMC surface consists of small patches of copper. DRA is mounted on the AMC surface, which significantly reduces the overall DRA volume. Nine AMC patches were introduced with a small gap between them. AMC patches were shorted with the ground metal with the help of small metallic vias. For an overall performance analysis, the design was fabricated, and measured results were taken. The fabricated design covers a bandwidth of 180 MHz for −10 dB reference value of the reflection coefficient, which is mainly used for 5G wireless application. The design has 14.2% impedance bandwidth. Based on the analysis made for the proposed design, it is found that this simple technique highly reduces the DR volume (85%) and ground surface (15.5%) while maintaining the overall performance of the square DRA.

Wideband millimeter-wave (mmWave) directional propagation measurements were conducted in the 32 GHz and 39 GHz bands in outdoor line-of-sight (LoS) small cell scenarios. The measurement provides spatial and temporal statistics that will be useful for small-cell outdoor wireless networks for future mmWave bands. Measurements were performed at two outdoor environments and repeated for all polarization combinations. Measurement results show little spread in the angular and delay domains for the LoS scenario. Moreover root-mean-squared (RMS) delay spread at different polarizations show small difference which can be due to specific scatterers in the channel.

Millimeter wave lens antennas will be essential for future wireless access. Conventionally, they increase the gain in the boresight direction only. In this paper, cascaded Fresnel zone plate lenses are combined with a phased array to increase the gain at wide steering angles of ±52°. The side lenses are tilted to align with the maximum steering angle, and cascaded to increase the focusing gain. The inner lenses increase the gain by 2.45 dB at boresight, and by 3.19 dB at the maximum steering angle. When the side lenses are repositioned, the simulated focusing gain increases to 4.69 dB. Asymmetric amplitude distributions are proposed to prevent the main lobe from splitting. An 8-dement 7-lens prototype operating at 28 GHz achieved a gain from 12.96 dBi to 15.35 dBi with a bandwidth of at least 1.3 GHz for all measured beam directions. The maximum measured azimuthal beamwidth was 27°. A design procedure and a theoretical analysis of diffraction through the lenses are provided. By increasing the SNR, this beamfonning antenna could improve the coverage of 3-sector 5G microcell base stations, and support gigabit wireless links for vehicular, rail, and satellite communications.

This paper presents details of the wideband directional propagation measurements of millimetre-wave (mmWave) channels in the 26 GHz, 32 GHz, and 39 GHz frequency bands in an indoor typical office environment. More than 14400 power delay profiles (PDPs) were measured across the 26 GHz band and over 9000 PDPs have been recorded for the 32 GHz and 39 GHz bands at each measurement point. A mmWave wideband channel sounder has been used, where signal analyzer and vector signal generator was employed. Measurements have been conducted for both co- and crossantenna polarization. The setup provided 2GHz bandwidth and the mechanically steerable directional horn antenna with 8 degrees beamwidth provides 8 degrees of directional resolution over the azimuth for 32 GHz and 39 GHz while 26 GHz measurement setup provides the angular resolution of 5 degrees. Measurements provide path loss, delay and spatial spread of the channel. Large-scale fading characteristics, RMS delay spread, RMS angular spread, angular and delay dispersion are presented for three mmWave bands for the line-of-sight (LoS) scenario.

This paper exploits a generic downlink symbiotic radio (SR) system, where a Base Station (BS) establishes a direct (primary) link with a receiver having an integrated backscatter device (BD). In order to accurately measure the backscatter link, the backscattered signal packets are designed to have finite block length. As such, the backscatter link in this SR system employs the finite block-length channel codes. According to different types of the backscatter symbol period and transmission rate, we investigate the non-cooperative and cooperative SR (i.e., NSR and CSR) systems, and derive their average achievable rate of the direct and backscatter links, respectively. We formulate two optimization problems, i.e., transmit power minimization and energy efficiency maximization. Due to the non-convex property of these formulated optimization problems, the semidefinite programming (SDP) relaxation and the successive convex approximation (SCA) are considered to design the transmit beamforming vector. Moreover, a low-complexity transmit beamforming structure is constructed to reduce the computational complexity of the SDP relaxed solution. Finally, the simulation results are demonstrated to validate the proposed schemes.

In this paper, a compact circularly polarized (CP) multi-mode antenna for global navigation satellite system re- flectometry (GNSS-R) is presented. The design comprises two Quadrifilar Helical Antennas (QHAs), each fed with a ground coplanar waveguide (GCPW) and quarter wavelength power divider (QWPD) integrated feed. A hybrid staircase-shaped (SSR) QHA radial is proposed, and it is formed by serially arranging several vertical and diagonal elements. The electric field lines from the vertical elements converge constructively to radiate with the axis normal. Besides, the circular spatial offsets between the adjacent diagonal and vertical elements induce a 90 delay in the field radiated. This hybrid shape launches an unprecedented theory facilitating normal mode of operation (MOOp) in QHA and generates CP over broad elevations and azimuths (0

A conformal transmitarray with thinned control is presented, operating at 28 GHz. Its side panels are rotated to align with the maximum steering angle, increasing the gain and reducing the scan loss. The transmitarray is fed by an 8-element linear phased array antenna. Beam focusing to +/- 53 degrees is demonstrated for two different directions, using combinations of crossed-slot unit cells. A unit cell placement rule is proposed to significantly reduce (i.e. thin) the required number of reconfigurable unit cells. A filling factor of 43% was achieved compared to a fully populated design. This reduces the cost and biasing complexity. By minimising scan loss, this antenna could improve the performance of 5G small-cell access points.

A statistical model is derived for the equivalent signal-to-noise ratio of the Source-to-Relay-to-Destination (S-R-D) link for Amplify-and-Forward (AF) relaying systems that are subject to block Rayleigh-fading. The probability density function and the cumulated density function of the S-R-D link SNR involve modified Bessel functions of the second kind. Using fractional-calculus mathematics, a novel approach is introduced to rewrite those Bessel functions (and the statistical model of the S-R-D link SNR) in series form using simple elementary functions. Moreover, a statistical characterization of the total receive-SNR at the destination, corresponding to the S-R-D and the S-D link SNR, is provided for a more general relaying scenario in which the destination receives signals from both the relay and the source and processes them using maximum ratio combining (MRC). Using the novel statistical model for the total receive SNR at the destination, accurate and simple analytical expressions for the outage probability, the bit error probability, and the ergodic capacity are obtained. The analytical results presented in this paper provide a theoretical framework to analyze the performance of the AF cooperative systems with an MRC receiver.

The paper presents a technique to enhance the isolation between adjacent radiating elements which is common in densely packed antenna arrays. Such antennas provide frequency beam-scanning capability needed in Multiple-Input Multiple-Output (MIMO) systems and Synthetic Aperture Radars (SARs). The method proposed here uses a metamaterial decoupling slab (MTM-DS), which is located between radiating elements, to suppress mutual-coupling between the elements that would otherwise degrade the antenna efficiency and performance in both the transmit and receive mode. The proposed MTM-DS consists of mirror imaged E-shaped slits engraved on a microstrip patch with inductive stub. Measured results confirm over 9–11 GHz with no MTM-DS the average isolation (S12) is -27 dB; however, with MTM-DS the average isolation improves to -38 dB. With this technique the separation between the radiating element can be reduced to 0.66λo, where λ0 is free space wavelength at 10 GHz. In addition, with this technique there is 15% improvement in operating bandwidth. At frequencies of high impedance match of 9.95 GHz and 10.63 GHz the gain is 4.52 dBi and 5.40 dBi, respectively. Furthermore, the technique eliminates poor front-to-back ratio encountered in other decoupling methods. MTM-DS is also relatively simple to implement. Assuming adequate space is available between adjacent radiators the MTM-DS can be fixed retrospectively on existing antenna arrays, which makes the proposed method versatile.

Unequally spaced arrays technique offers an alternative for limited sidelobe level reduction compared to conventional array antennas with equally spaced elements. In this paper, the abilities and design of microstrip linear array antenna, fed by multiport feeding with uniform excitation coefficient in all array elements are presented for sidelobe level reduction at 28 GHz. By using the proximity coupled feed, simulation result gave -10 dB impedance bandwidth of 1.42 GHz and reflection coefficient of -35.5 dB has been achieved. The sidelobe level at broadside decreased from -11.77 dB to -14.76 dB (N = 4) and -12.77 dB to -15.98 dB (N = 8) with unequally spaced array. This feature is suitable for 5G applications.