Chunxu Mao

Based on characteristic mode theory (CMT), a quad-polarization reconfigurable antenna with suppressed cross polarization is proposed in this article. The proposed antenna is composed of the radiator, excitation units, and feeding network. A square conductive slab (SCS) is used as the main radiator, which is designed elaborately by characteristic mode analysis (CMA). Different modes of the radiator are stimulated selectively by four groups of balanced inductive exciters (BIEs) to realize horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Two p-i-n diodes are embedded into the feeding network to switch the excitation states of the four groups of BIEs, thereby achieving quad-polarization reconfiguration. More importantly, a novel method exploiting the CMA is adopted for achieving low cross polarization. By means of introducing the orthogonal mode, the cross-polarization component of the fundamental mode can be canceled out by the co-polarization component of the orthogonal mode, which greatly reduces the cross polarization from −10 to −40 dB in the two principal planes. The measurement results demonstrate that the quad-polarization agility and a cross-polarization level around −30 dB under all polarization states are achieved simultaneously, verifying the functionality and reliability of the proposed method.

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.

This letter investigates a highly integrated dual-polarized duplex antenna for modern base-station systems. The antenna comprises a pair of orthogonally placed dipole radiators, duplexer-integrated baluns (DIBs), and a reflector. The duplex function is achieved by integrating the dipole radiators with the highly isolated DIBs, using λ/4 parallel-coupled resonators and a U-shaped resonator. For each polarization, the antenna has two isolated ports for the low band and high band operations, enabling duplex operation. The antenna has a compact size of 0.35 λ L0 × 0.35 λ L0 × 0.17 λ L0 , where λ L0 denotes the free-space wavelength at the center frequency of the low band. Both simulation and measurement results demonstrate that each polarization of the antenna can simultaneously support two operation bands, respectively from 3.42 to 3.60 GHz and from 4.80 to 5.10 GHz. The interband isolation and polarization isolation are higher than 20 and 30 dB, respectively. The proposed antenna represents an appealing candidate for 5G sub-6 GHz base-station applications.

In this paper, a novel center-fed leaky-wave antenna with four beams for millimeter-wave applications is proposed. The wide-angle beam scanning characteristic is achieved by choosing an appropriate unit cell and utilizing a broadband feeding structure. The unit cell consists of two pairs of identical slots etched on both layers of the substrate integrated waveguide (SIW), and a wideband magic-T is embedded in the middle of SIW to provide an out-of-phase equal amplitude excitation. In such a way, quad-beam radiation is obtained. Each beam can scan from near end-fire to broadside direction, and the forward radiation beams are not used in the proposed design, which further increases the beam-scanning rate. Moreover, with the coexistence of the proposed leaky-wave structure and the two-way SIW power divider, multiple beams can be implemented using only one input port in a low-cost manner. Simulated results illustrate that a wide bandwidth of 27.7% is obtained from 22.5 GHz to 29.75 GHz with vertical bar S-11 vertical bar below -10 dB. Moreover, the proposed antenna can provide an overall beam-scanning range of 284 degrees, with each beam-scanning range of 71 degrees.

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 paper presents the integration and channel characterization of a highly integrated dual-band digital beamforming space-borne synthetic aperture radar (SAR) receiver. The proposed SAR sensor is a low-cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module ready for the next-generation space-borne SAR missions. In previous works, by the authors, the design and experimental characterization of each sub-system was already presented and discussed. This work expands upon the previous characterization by providing an exhaustive experimental assessment of the fully integrated system. As it will be shown, the proposed tests were used to validate all the instrument channels in a set-up where the SAR sensor was illuminated by an external source minim the ground reflected waves. Test results demonstrate how the system channels are properly operating allowing the reception of the input signals and their processing in the digital domain. The possibility to easily implement a calibration procedure has also been validated to equalize, in the digital domain, the unavoidable amplitude differences between the different channels.

A dual-beam filtering patch antenna with two absorptive band-edge radiation nulls and four reflective stopband radiation nulls is proposed. By loading a pair of T-shaped metallic strip underneath the radiating patch, a modified TM 22 mode with TM 20 -like radiation pattern is obtained, which combines with the TM 20 mode of the radiating patch, generating a wide operating band with symmetrical dual-beam radiation pattern. Two reflective radiation nulls are generated in both upper and lower stopbands for suppressing the out-of-band radiation. Through embedding two pairs of shorted small patch in the radiating patch, one absorptive radiation null combining with one absorptive resonant mode is produced at each band edge to absorb the band-edge incident energy, leading to a reduced reflection and sharp roll-off at both band edges, and therefore, the transceiver can be protected. With a total height of 0.038~\lambda _{0} , a prototype is designed, fabricated, and measured, showing a −10 dB impedance bandwidth from 4.63 to 6.10 GHz with sharp band-edge roll-off, two radiation beams directed at ±40° with an in-band gain of 6.0 dBi, and high out-of-band suppression of over 15 dB.

A novel low-cost, dual-polarized, 2-D leaky wave antenna (LWA) with four beams is proposed in this article. The proposed 2-D LWA includes a 2-D leaky wave radiation aperture and an orthogonal feeding network. The 2-D leaky wave radiation aperture is evolved from two identical 1-D parallel-plate long-slot LWAs that are orthogonally placed within a shared radiation aperture. Based on the proposed feeding networks, two pairs of orthogonal in-phase excitations are provided for the proposed 2-D radiation aperture to realize four beams with orthogonal polarizations. Combining the frequency-controlled beam-scanning characteristic of the 2-D LWA in the elevation plane and the quad-beam radiation by the proposed feeding network in the azimuth plane, a wide-angle beam-scanning characteristic can be realized. Besides, different from the conventional multibeam antenna with multiple feeding ports or multiple radiation apertures, only a simple coaxial feeding port and single aperture are used, which greatly reduces the complexity and cost of the antenna. A prototype for verifying the design concept is manufactured and measured. The measurement results illustrate that the antenna supports a wide beam-scanning range around ±83° except for broadside direction in two orthogonal elevation planes with orthogonal polarizations. Furthermore, a wide operating bandwidth from 23 to 33.6 GHz with a peak realized gain of 21.2 dBi is obtained by the antenna. The low-profile, quad-beam, dual-polarized, wideband, high-gain, low-cost, and wide-angle beam-scanning features make the proposed antenna suitable for various millimeter-wave applications.

In this article, a novel dual-polarized embroidered textile antenna array with an omnidirectional radiation pattern is proposed for both on- and off-body wearable applications. The flexible antenna is composed of a group of circularly oriented dual-polarized patch antennas excited with uniform amplitude and phase. The antenna array can be wrapped around a cylinder, such as an arm or a leg, for realizing a quasi-omnidirectional radiation pattern in the azimuthal plane, which is highly desirable in both on-body and off-body wearable applications. The operating principles and design consideration for how to achieve the omnidirectional radiation and how to avoid radiation nulls are investigated in detail. Moreover, these analytical studies are verified through the experimental results. In addition, a dual orthogonal polarization capability is employed to improve the link reliability. Due to the high front-to-back ratio (FBR) exhibited by each patch antenna element, the proposed omnidirectional antenna array also features a low specific absorption rate (SAR) and high efficiency, which are extremely important for wearable applications. As a proof-of-concept, an antenna array prototype operating at 5.8 GHz is designed, fabricated, and tested. The measured results agree reasonably well with the simulations in terms of S-parameters, polarization isolation, and radiation patterns, demonstrating that the proposed antenna array is ideally suited for potential wearable applications.

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.

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.

A novel miniaturized wideband dual-polarized antenna, based on cross magnetic dipoles and a backed cavity, is proposed in this letter for multiple-input-multiple-output (MIMO) applications. The dipoles with exponential curvature edges deliver inherent wideband character to the radiator. Four parasitic resonators are introduced to miniaturize the top radiator's conducting area and lower the Q-factor of the whole structure, enhancing the antenna's impedance matching. Different from conventional direct-fed cross-dipole antennas, a wideband hybrid ring coupler is applied to excite the two dipoles simultaneously in-phase/out-of-phase to generate the +/- 45 degrees polarization. The dimension of the proposed antenna is 42.5 mm x 42.5 mm x 18 mm, which is only 0.48 lambda(L) x 0.48 lambda(L) x 0.2 lambda(L) at the frequency of 3.4 GHz. The corresponding MIMO array is studied, showing a low mutual coupling and envelope correlation coefficient level across the band, and an outperforming front-back-ratio performance. The antenna is prototyped and measured. The measurement results agree with those of the simulations well

Optical activity is the ability of chiral materials to rotate linearly polarized electromagnetic waves. A knotted chiral metamolecule is introduced here that exhibits strong optical activity corresponding to a 90 degrees polarization rotation of the incident waves. More importantly, the torus knot structure is intrinsically chiral and multifold axisymmetric. Consequently, the observed polarization rotation behavior is found to be independent of how the incident wave is polarized. The metamolecule is fabricated through selective laser melting and experimentally validated in the microwave spectrum. This work represents the first ever metamolecule to be reported that is intrinsically axisymmetric and capable of simultaneously exhibiting strong optical activity.

An ultrawideband stacked single-turn spiral antenna with an integrated feeding structure is presented in this communication. The proposed antenna consists of two stacked planar single-turn Archimedean spirals which are wound in orthogonal directions. By connecting these two stacked spirals through two vertical posts, the traveling-wave current path is lengthened and, hence, the operating frequency of Mode 1 is decreased. To reduce the feeding complexity, an integrated tapered microstrip line is used to feed the spiral, which also acts an impedance transformer. It is demonstrated that the proposed antenna can operate across 0.29-5 GHz with |S 11 | < −10 dB and 0.75-3.64 GHz with axial ratio (AR) < 3 dB. Compared with the single-turn Archimedean spiral with the same radius, the impedance and AR bandwidth of the proposed antenna are enhanced from 5:1 to 17:1 and from 1.6:1 to 4.9:1, respectively, showing that the proposed antenna can be a good candidate for ultrawideband applications.

A compact millimeter-wave polarizer that transforms a linear polarization wave into circular polarization is proposed in this paper. The presented polarizer is made of a single-layer metal plate with three ring slots, and the simulated annealing algorithm (SA) is used to optimize the size of the ring slots, which is much more efficient than the manual optimization using commercial EM tools. The optimized resonant frequency of the proposed polarizer is 30GHz, with a 3dB axial ratio (AR) bandwidth of 10%, and a minimum AR value of 0.3 dB at 30GHz.

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.

A compact, low-profile, dual-band (2.4/5.8 GHz) omnidirectional circularly polarized (CP) antenna for consumer Unmanned Aerial Vehicle (UAV) communications is proposed. Given the constraints of UAV installation, we incorporate complex miniaturization etching techniques into the antenna design. The low-frequency resonance is primarily realized by four short-terminated arcs, while the high-frequency resonance is predominantly induced by four open-terminated branches. In addition, a dual-band coupled strip-line filter is cascaded to the radiator, enhancing the design's bandwidths. A prototype of the antenna is simulated, fabricated, and measured, resulting in final dimensions of 0.2 × 0.2 × 0.042λ 0 3 (λ 0 is the free-space wavelength at 2.4 GHz). The -10 dB | S 11 | and 3 dB Axial Ratio (AR) overlapped bandwidths reach 40 and 125 MHz for the low- and high-frequency bands, respectively. Lastly, we present an example of integrating the antenna into a quadcopter UAV and briefly discuss the potential of applying this antenna for a Multiple-Input, Multiple-Output (MIMO) system.

A novel dual-port textile antenna with a low profile and enhanced bandwidth is proposed for 2.45 GHz IMS-band full-duplex wearable applications. The antenna is developed on a textile material by using an advanced screen-printing technology and, thus, exhibits a very good structural flexibility and a high manufacturing accuracy. To improve the bandwidths at the two input ports, an innovative method is introduced for the first time where two additional strips are incorporated into the antenna design. These additional strips are placed perpendicularly to the feed lines to generate another resonant frequency, which is then combined with the fundamental mode of the patch antenna, producing the second-order resonant properties with enhanced bandwidths. The proposed strips are also beneficial to significantly improve the isolation between the two channels/ports. To maintain a robust linkage, a study of structural deformation is carried out by bending the antenna along both the 0° and 45° directions. The experimental results also show that the antenna is robust to the human tissue loading, where the specific absorption rate (SAR) is lower than 0.37 W/kg when the antenna is fully attached. The measured results agree reasonably well with the simulations providing experimental verification of the design concept. The antenna is believed to be the first dual-mode textile antenna of its type which features a low profile, improved bandwidth, high isolation, and low cost, making it a good candidate for potential full-duplex wearable applications.

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.

This paper presents a compact dual-band filtenna with controllable radiation nulls for Shark-Fin scenarios. The proposed filtenna is composed of three quarter-wavelength dual-band resonators. The resonator in the middle is fed by the probe. The other resonators on both sides of the middle resonator are coupled by the mixed electromagnetic (EM) field. Since the electric and magnetic couplings can be cancelled, the mixed EM coupling can be used to obtain more radiation nulls with less order than the other coupling mechanisms. Thus, the proposed antenna is straightforward and compact. Furthermore, the dual-band Quasi-elliptical responses are realized. Four radiation nulls are realized on both sides of two pass-bands, and the positions can be flexibly adjusted in dual bands. Without extra filtering circuits, high radiation efficiency can be achieved. To analyze and guide antenna design, the RLC equivalent circuit and extraction method are provided. For demonstration, the proposed filtenna is implement-ed. Radiation efficiency is about 64% and 83% within 2.4-2.5 GHz and 5.0-5.88 GHz, respectively. Moreover, the out-of-band supp-ression is over 20 dB. Compared with the traditional antenna, the in-band radiation performance of the proposed antenna is almost maintained, whereas out-of-band suppression is significantly enhanced. The proposed filtenna is suitable for Shark-Fin scenar-ios where multiple antennas operating at different frequency bands coexist. The interference from antennas at adjacent bands is reduced significantly due to the out-of-band suppression. Specially, the isolation between the proposed dual-band filtenna and antennas operating at the other bands can be improved by about 21 dB.

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 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.

A low-profile compact tri-band (2.45/3.5/5.8 GHz) reconfigurable antenna with versatile radiation modes is proposed for portable wireless communication in this communication. The characteristic mode analysis method is used to explain the antenna's operating principles and reduces the dimension. The antenna primarily comprises a patch radiator with T-shaped cuts, meander-slot defected ground, and shorting pins, resulting in three frequency bands with different radiation patterns. The antenna features a compact volume of 0.24\lambda _{0} \times 0.24\lambda _{0} \times 0.026\lambda _{0} ( \lambda _{0} is the free-space wavelength of 2.45 GHz) and exhibits omnidirectional radiations at 2.45 and 5.8 GHz and unidirectional radiations at 3.5 GHz. In addition, the operating bands can be tuned by applying different dc biases to the varactors. The antenna is fabricated, and the measured results agree reasonably well with the simulations. The miniaturized tri-band antenna can be potentially used in portable wireless services and intelligent transport devices.

In this paper, a compact and low-profile proximity-fed textile-based antenna with robust performance and improved bandwidth is proposed for body-area network (BAN) applications. The employed proximity-fed antenna differs from traditional wearable antennas in the sense that it not only exhibits improved bandwidth but also a reduced footprint. The proposed antenna also possesses an extreme robustness when subject to structural deformation and human body loading effects. In addition, the impact of the uncertainty in the dielectric constant (a characteristic associated with most textile material systems) is investigated for the first time. Experimental results show that the proposed proximity-fed antenna outperforms wearable antennas that employ more conventional feeding methodologies. The antenna was fabricated using two different flexible textile-based material systems (i.e., one printed and one embroidered). The advantages and disadvantages of each fabrication approach are discussed. The proposed antenna is characterized in free-space and on a human body, yielding robust performance in both cases.

A novel ultra-wideband (UWB) reflectarray antenna for the Internet of Vehicles (IoV) is introduced in this paper. By simply connecting the neighboring reflectarray elements, the proposed reflectarray antenna achieves a remarkable radiation pattern bandwidth of 20 GHz, ranging from 10 GHz to 30 GHz. To explain the operating principles of the proposed reflectarray antenna, the equivalent circuit (EQC) model of the unit cell is built, which also provides an efficient and rapid way to analyze the performance of the proposed reflectarray element. It is found from the EQC analysis that the connected elements can achieve better reflection phase responses than conventional separated elements, thereby improving the array bandwidth. As a proof of concept, a 503-element reflectarray antenna simultaneously covering the vehicle-to-satellite bands (12.25-12.75 GHz/14.0-14.5 GHz/19.6-21.2 GHz/29.4-31.0 GHz), the 24-GHz short-range vehicle radar band (24.25-26.65 GHz) and the 5G millimeter-wave band (27.5-28.35 GHz) is designed, fabricated, and characterized. The experimental results demonstrate that the presented reflectarray antenna can maintain undistorted beams, high antenna gain, low cross-pol level, and moderate aperture efficiency over a bandwidth of 100%, i.e., from 10 to 30 GHz. With its simple and planar aperture as well as excellent performance, the proposed reflectarray antenna can be a promising candidate for vehicles that require reliable high data-rate satellite links and 5G millimeter-wave connections simultaneously.

A compact pattern diversity patch antenna working at 5.8 GHz is proposed. The patch antenna has two ports, which are responsible for the broadside radiation and omni-directional radiation, respectively. The broadside radiation is achieved by inserting a substrate slot-loaded integrated waveguide (SIW) cavity at the center of the patch antenna, and the omni-directional pattern is realized by exciting the shorted patch in-phase from both sides of the SIW cavity. Although the two operating modes share the same radiator, but a high isolation of over 30 dB is achieved, due to the cancellation of current at the inputs. In addition, two approaches are investigated to enhance the operation bandwidths. The pattern diversity antenna is prototyped and measured, showing an impedance bandwidth of 5.69-5.92 GHz for both modes/channels, and a high inter-channel isolation over 30 dB, making it suitable for indoor wireless communication systems.

In this paper, a waveguide-type reflectarray element is designed and used to form a 16 x 16 reflectarray antenna which generates a pencil beam pointing to the broadside direction. The element consists of a dielectric filled waveguide, and copper wires that reflect the incident waves. The simulation results indicate that the reflectarray antenna can achieve stable high-gain beam from 25 to 35 GHz with low sidelobe level (SLL). The merits of high gain, low profile and wide bandwidth make the proposed reflectarray antenna a promising candidate for millimeter-wave applications and 5G.

This paper presents a novel center-fed leaky-wave antenna (LWA) with a broad beam-scanning range. Different from the traditional LWA with a single beam, the proposed LWA consists of a magic-T for providing an out-of-phase equal-amplitude excitation and a periodic LWA array based on substrate integrated waveguide (SIW) for radiation. A dual-beam antenna supporting a wide-scanning range through the broadside without the open stopband suppression can be realized. It should be noted that only the backward radiation beams are used in the design. A broad bandwidth of 27.7% (22.14-29.25 GHz) is achieved, according to the simulation findings. Moreover, the simulated radiation patterns illustrate that a wide range of beam scanning around +/- 75 degrees including broadside direction is achieved by the proposed antenna. With its broad operating frequency band and wide-scanning angle, the proposed design shows promise for varies applications.