Showing papers in "IEEE Antennas and Wireless Propagation Letters in 2018"

Glide-Symmetric Fully Metallic Luneburg Lens for 5G Communications at K a -Band

Abstract: Here, we propose a fully metallic implementation of a Luneburg lens operating at Ka-band with potential use for 5G communications. The lens is implemented with a parallel plate that is loaded with glide-symmetric holes. These holes are employed to produce the required equivalent refractive index profile of a Lune-burg lens. Glide symmetry and inner metallic pins are employed to increase the equivalent refractive index. The lens is fed with rectangular waveguides designed to match the height of the parallel plate, and it is ended with a flare to minimize the reflections.

Wearable Circular Ring Slot Antenna With EBG Structure for Wireless Body Area Network

Abstract: A wearable circular ring slot antenna with electromagnetic bandgap (EBG) structure for wireless body area network application is proposed in this letter. According to the analysis of equivalent circuit model, the volume of the EBG element is miniaturized for wearable applications. The measured impedance bandwidth of the proposed antenna is observed to be 2.28–2.64 GHz, which covers the 2.4 GHz Industrial Scientific Medical (ISM) band. The measured half-power beamwidths are 60° and 54° in the H -plane and the E -plane, respectively, and the front-to-back ratios are 17 and 13 dB in the H -plane and the E -plane, respectively. The specific absorption rate calculated values for tissue in 1 g (for the U.S. standard) and 10 g (for Europe standard) are both less than the limitations. In conclusion, it is proper to use the proposed antenna in wearable applications.

A Compact Gain-Enhanced Vivaldi Antenna Array With Suppressed Mutual Coupling for 5G mmWave Application

Abstract: In this letter, a novel method of reducing mutual coupling is proposed, and it used on a modified compact broadband antipodal Vivaldi antenna (AVA) array for future 5G millimeter-wave (mmWave) communication application. The proposed structure consists of eight antenna elements that are fed by a 1-to-8 power divider. In order to reduce the mutual coupling between AVA array elements, multiple notch structures are added on the ground plane. Thus, the isolation between the antenna elements can achieve a maximal additional 37.3 dB enhancement, impedance bandwidth is extended slightly from 24.65–28.5 GHz to 24.55–28.5 GHz, and the gain is improved simultaneously. To verify the designed method, the proposed AVA arrays were fabricated and measured. They show an overall size of 28.823 mm × 60 mm × 0.787 mm. The measured gain of the modified AVA array is 6.96–11.32 dB in the frequency band of future 5G mmWave communication, which is higher than the initial AVA array, whose gain is 5.34–8.5 dB.

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

Abstract: A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y / x -polarized incident EM wave can be converted to the x/y -polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y / x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.

UWB Wearable Antenna With a Full Ground Plane Based on PDMS-Embedded Conductive Fabric

Abstract: A new flexible ultrawideband (UWB) antenna is presented for wearable applications in the 3.7–10.3 GHz band, which is highly tolerant to human body loading and physical deformation. The antenna exhibits a footprint of 80 mm $\times$ 67 mm and is based on a simple microstrip structure with two modified arc-shaped patches as the main radiator. A full ground plane is maintained on the opposite side of the substrate to suppress antenna loading from the underlying biological tissues and back radiation directed toward the human body. For enhanced flexibility and robustness, the proposed antenna is realized using conductive fabric embedded into polydimethylsiloxane polymer. Promising simulation and experimental results are presented for free-space and in-vitro wearable scenarios. To our knowledge, this is the first UWB antenna with a full ground plane that is concurrently highly tolerant to harsh operating conditions, such as those encountered in wearable applications.

A Compact Dual-Band Dual-Polarized Antenna With Filtering Structures for Sub-6 GHz Base Station Applications

Abstract: This letter presents a novel compact dual-band dual-polarized antenna with filtering structures for Sub-6 GHz base station applications. It is operating at the LTE (2500–2690 MHz) and Sub-6 GHz of 5G (3300–3600 MHz) bands, where the center frequency of upper-band (UB) is 1.32 times of lower-band (LB). Mutual coupling between LB and UB is suppressed by the introduction of the filtering stubs near the feeding lines. A sufficiently high isolation between LB and UB (>25 dB) is also obtained. The size of the proposed antenna is only 0.43 ${{\rm{\lambda }}_1} \times \text{0.43}$ ${{\rm{\lambda }}_1} \times \text{0.26}$ ${{\rm{\lambda }}_{1}}$ ( ${{\rm{\lambda }}_1}$ is the free-wavelength at 2.6 GHz). The half power beam widths are 65° ± 5° over both bands at horizontal planes. A four-element array, which consists of four hybrid antennas (the UB element is nested in the LB element) with a small array width (only 105 mm) is also studied. The proposed antenna and its array are suitable for wireless communication applications.

Pattern-Reconfigurable Antenna With Five Switchable Beams in Elevation Plane

Abstract: Pattern-reconfigurable antennas with multiple switchable beams, especially with both boresight and endfire directions, are highly desired for wireless communications. In this letter, a novel pattern-reconfigurable antenna is proposed that provides an efficient solution. By reconfiguring parasitic striplines placed around a radiating dipole and reflecting metal pieces under the dipole using p-i-n diodes, the antenna main beam can be switched to five directions in the elevation plane, approximately from $-90^{\circ }$ (left endfire), $-45^{\circ }$ , 0 $^{\circ }$ (boresight), $+45^{\circ }$ , to $+90^{\circ }$ (right endfire). The proposed antenna operates at 2.45 GHz with dimensions of about 0.57 $\lambda$ $\times\, 0.45\lambda$ $\times\, 0.28\lambda$ . An antenna prototype is fabricated and measured. For all five directional beams, the measured $|S_{11}|$ values are below $-$ 13 dB, and the measured realized gains range from 5.2 to 6.5 dBi. They agree reasonably well with the simulated ones.

Design of Frequency Selective Surface Structure With High Angular Stability for Radome Application

Abstract: A design method for frequency selective surface (FSS) structure with high angular stability has been proposed in this letter. In the proposed method, bandwidth angular stability of FSS structure has been improved by adopting the bandwidth compensation technique, and structural parameters can be obtained with a curve-fitting method from the desired resonate frequency and bandwidth. Discussions on improving the bandwidth design accuracy have been presented. By taking bandwidth angular stability into consideration, the structure designed by the proposed method is more suitable to construct FSS radome. For verification, an FSS structure operating at 15 GHz with a bandwidth of 2 GHz has been designed, fabricated, and measured. Good agreements between the simulated and measured results can be observed.

Classification of Indoor Environments for IoT Applications: A Machine Learning Approach

Abstract: Evolving Internet-of-Things (IoT) applications often require the use of sensor-based indoor tracking and positioning, for which the performance is significantly improved by classifying the type of the surrounding indoor environment This classification is of high importance since it leads to efficient power consumption when operating the deployed IoT sensors This letter presents a machine learning approach for indoor environment classification based on real-time measurements of the radio frequency (RF) signal in a realistic environment Several machine learning classification methods are explored including decision trees, support vector machine, and $k$ -nearest neighbor using different RF features Results obtained show that a machine learning approach based on weighted $k$ -nearest neighbor method, which utilizes a combination of channel transfer function and frequency coherence function, outperforms the other methods in classifying the type of indoor environment with an accuracy of 993% The predication time was found to be below 10 $\mu$ s, which verifies that the adopted algorithm is a successful candidates for real-time deployment scenarios

Design of Frequency-and Polarization-Reconfigurable Antenna Based on the Polarization Conversion Metasurface

Abstract: A frequency- and polarization-reconfigurable antenna composed of a metasurface, a planar slot antenna, and a metallic reflector is proposed in this letter. The metasurface is made up of 64 identical patches, and all the patches are on the top surface of the substrate. In order to extend the bandwidth of the antenna, the planar slot antenna adopts a double-slot structure. The reconfiguration of frequency and polarization can be achieved by adjusting the relative positions between the metasurface and the planar slot antenna. The antenna can be reconfigured to linear polarization, and left-hand and right-hand circular polarizations. At the same time, the gain of the antenna is improved. In order to verify this method, a frequency- and polarization-reconfigurable antenna is designed. Simulation and experimental results show that the polarization reconfiguration can be achieved from 8 to 11.2 GHz (fractional bandwidth of 33.33%) by adjusting the distance among the metasurface, source antenna, and metallic reflector. The maximum gain can achieve 16.5 dBi.

A Simple Planar Pattern-Reconfigurable Antenna Based on Arc Dipoles

Abstract: A simple compact planar pattern-reconfigurable antenna based on arc dipoles is proposed in this letter. The antenna consists of four identical arc dipoles and a broadband reconfigurable feeding network, which are printed on the bottom and top layers of the substrate, respectively. By switching the on/off states of the p-i-n diodes, which are integrated in the reconfigurable feeding network, four different modes with endfire radiation patterns can be obtained in the azimuthal plane. The antenna is simulated, fabricated, and measured. Experimental results indicate that the proposed antenna achieves a bandwidth of 33.6% (2.25–3.16 GHz) for impedance matching better than 10 dB. The measured average gain is 4.11 dBi. Furthermore, the radiation efficiency is up to 60%. The proposed antenna is suitable for WLAN applications in wireless communications.

Design of a Wideband Omnidirectional Antenna With Characteristic Mode Analysis

Abstract: A low-profile horizontally polarized (HP) omnidirectional metasurface-inspired antenna is presented. To realize HP omnidirectional radiation pattern, the theory of characteristic mode is utilized to facilitate the analysis of three antenna structures. Then, by properly exciting the desired characteristic mode, the antenna with a wide bandwidth and good omnidirectionality, which is based on the modification of the standard patch antenna, is obtained. The simulated results show that the proposed antenna not only can obtain a low profile of 0.06 λ 0 (where λ 0 is the free-space wavelength at 5.2 GHz), but also has a wide operating bandwidth of 16.6%. Finally, the metasurface-inspired antenna is manufactured and the error analysis between the simulated and measured results is also provided. The antenna can be applied to 5G wireless local area network systems.

Expedited Design Closure of Antennas by Means of Trust-Region-Based Adaptive Response Scaling

Abstract: In this letter, a reliable procedure for the expedited design optimization of antenna structures by means of trust-region adaptive response scaling (TR-ARS) is proposed. The presented approach exploits two-level electromagnetic (EM) simulation models. A predicted high-fidelity model response is obtained by applying nonlinear frequency and amplitude correction to the low-fidelity model. The surrogate created this way is iteratively rebuilt and optimized within the trust region framework. The utilization of the correlations between the EM models of various fidelities allows for significant reduction of the design optimization cost. The main contributions of the work are twofold: 1) the application of an ARS for antenna optimization (in particular, making it work with coarse-discretization EM models as low-fidelity models); and 2) the integration of an ARS with a TR optimization framework. The operation and performance of the algorithm are demonstrated using two antenna designs optimized for several scenarios. A comparative study reveals computational benefits of the TR-ARS over direct optimization of the high-fidelity EM model. The reliability of the optimization process is further confirmed by an experimental validation of the fabricated antenna prototypes.

A 3-D-Printed W -Band Slotted Waveguide Array Antenna Optimized Using Machine Learning

Abstract: A three-dimensional (3-D) printed W -band slotted waveguide array antenna (SWAA) is proposed. The proposed SWAA consists of three different sections (two horizontal ones and a vertical one) such as a radiating waveguide array with 10 × 10 slots array with an aperture size of 31 mm × 31.4 mm, a coupling waveguide to feed the radiating waveguide array, and a vertical waveguide to feed the coupling waveguide. Machine learning technique based on artificial neural network algorithm is used to optimize the design. The optimized SWAA is fabricated using stereolithography apparatus (SLA) 3-D printing and then is metallized with silver on the inner and outer surfaces by jet metal spraying method. To metallize the inner and outer surfaces of the monolithic structure, nonradiating slots are added on the surface of the designed SWAA. The surface roughness is taken into account by employing the Huray-model methodology in simulation. The SWAA has a 22.5 dBi far-field gain, a −13.5 dB sidelobe level, and 10° half-power beamwidth (HPBW) at 78.7 GHz in measurement.

A SAR Reduced mm-Wave Beam-Steerable Array Antenna With Dual-Mode Operation for Fully Metal-Covered 5G Cellular Handsets

Abstract: In this letter, a specific absorption rate (SAR) reduced 28 GHz beam-steering array antenna with dual-mode operation for a fully metal-covered fifth-generation (5G) cellular handset is proposed. The proposed antenna consists of two subarrays, each of which has eight rotated slot antenna elements, which are arranged on the upper frame and on the part of the back cover of the handset. The subarrays are selected according to the modes by using a switch. The proposed array demonstrates good reflection coefficients in the frequency band ranging from 27.2 to 28.2 GHz and the mutual couplings between antenna elements are less than –11.8 dB. The proposed antenna has good beam-steering properties and a hemispherical beam coverage for a millimeter-wave (mm-wave) 5G cellular handset. The calculated peak SAR values on the head phantom by the proposed structure, for the beam scan angles of 0° and 40°, are 0.53 and 0.88 W/kg, respectively, when the input power of each subarray is 24 dBm.

A High-Gain Circularly Polarized Fabry–Perot Antenna With Wideband Low-RCS Property

Abstract: In this letter, a low radar cross section (RCS) and the high-gain circularly polarized (CP) antenna using a novel linear-to-circular polarization converter is presented. A simple linearly polarized patch antenna rotated 45° relative to x -axis is used as the primary source. The polarization converter is an asymmetrical metastructure composed of different metal patterns printed on the two sides of a dielectric substrate, which can transmit a CP wave. The top-side metallic pattern is an absorbing surface to realize the RCS reduction, while the bottom-side one is a partially reflective surface (PRS). A CP Fabry–Perot resonance cavity is constituted by the PRS and the anisotropic high-impedance surface (HIS) plane to obtain the gain enhancement. The simulation and measured results demonstrate that the proposed antenna exhibits good circular polarization performance in the operating frequency. In addition, the gain of the proposed antenna can be improved by about 3.2 dB at 10.7 GHz, and the RCS can be reduced significantly over a wideband ranging from 4 to 13 GHz for both polarizations, compared with the conventional patch antenna.

A Frequency- and Pattern-Reconfigurable Two-Element Array Antenna

Abstract: A frequency- and pattern-reconfigurable two-element array antenna based on a stub-loaded configuration is presented. The frequency-tuning mechanism is implemented using varactor diodes loaded with open stubs. Two independent bias voltages allow to independently add pattern reconfigurability to the array. This is achieved by slightly detuning the resonances of the two patches, thus introducing a beam-steering relative phase difference between them. The design is optimized for a relative frequency tuning range of $\text{10}\%$ extending from 2.15 to 2.38 GHz, within which it presents a continuously beam-steerable radiation pattern covering scanning angles from $-\text{23}^{\circ }$ to $+ \text{23}^{\circ }$ across broadside. An antenna prototype is experimentally characterized, which validates the proposed concept.

A Miniaturized Extremely Close-Spaced Four-Element Dual-Band MIMO Antenna System With Polarization and Pattern Diversity

Abstract: We propose a miniaturized design of a four-element dual-band multiple-input–multiple-output (MIMO) antenna system. The dual-band function is obtained by etching an “L” slot in the radiating patch. The edge-to-edge elements spacing is only 0.023 λ0 . A decoupling structure consisting of cross-shaped metal strips shorted to the ground plane using vias is first introduced. Then, metalized walls are used to enhance the isolation level by realizing the pattern diversity. The measured resonant frequencies are centered at 3.5 and 5.7 GHz with bandwidths of 58 and 43 MHz, peak gains of 2.7 and 2.85 dBi, and peak efficiencies of 63% and 65%, respectively. A considerable measured mutual coupling reduction of 10.8 dB in the lower band and 15.6 dB in the upper band is realized. The overall size of the design is 0.41λ0 × 0.41λ0 × 0.04λ0 with minimum isolation levels of 18.4 and 22.7 dB in the lower and upper bands, respectively. The envelope correlation coefficient is lower than 0.08 across both operating bandwidths. The measured results validate the good diversity performance of the MIMO system.

Reconfigurable Linear-to-Linear Polarization Conversion Metasurface Based on PIN Diodes

Abstract: A reconfigurable linear-to-linear polarization conversion metasurface (Re-PCM) based on positive-intrinsic-negative (PIN) diodes is proposed, which can be reconfigured between the conversion mode and the reflection mode by switching the loaded PIN diodes. The unit cell of the Re-PCM consists of two slotted metal square rings and bias lines, which are all etched on a substrate backed by a metal ground. In the conversion mode, the Re-PCM reflects linearly polarized incident waves with 90° polarization rotation. The simulated results show that the polarization conversion ratio is more than 88% over 3.39–5.01 GHz for x -polarized and y -polarized normally incident waves. In the reflection mode, it exhibits total reflection characteristic like a metal plate. The magnitude of co-polarization reflection is over −1 dB from 3.83 to 4.74 GHz. The physical mechanism and equivalent circuit of the Re-PCM are analyzed. To validate the simulation, a prototype of the Re-PCM is fabricated and measured. Reasonable accordance between the simulated and measured results is obtained.

An Implantable and Conformal Antenna for Wireless Capsule Endoscopy

Abstract: This letter proposes an implantable antenna with ultrawide bandwidth operating in the medical device radio communications service band (401–406 MHz) for the wireless capsule endoscopy (WCE). The simulation and experimental results show the proposed antenna has a good performance in terms of the return loss and hence the bandwidth from 284 to 825 MHz. The maximum realized gain of this antenna is –31.5 dBi at 403 MHz. The maximum simulated input power is <1.7 mW in order to satisfy the specific absorption rate (SAR) regulations in the IEEE standard. The tolerance of the antenna owing to bendability and different WCE shell thicknesses is investigated. These indicate that the proposed antenna is a good candidate for the WCE.

Double-Differential-Fed, Dual-Polarized Patch Antenna With 90 dB Interport RF Isolation for a 2.4 GHz In-Band Full-Duplex Transceiver

Abstract: This letter presents a 2.4 GHz, dual-polarized microstrip patch antenna with extremely high interport isolation for a shared antenna architecture-based in-band full-duplex transceiver. The presented antenna configuration is based on four-ports linearly polarized single radiating element with differential feeding for both transmit $(T_{x})$ and receive $(R_{x})$ operation. The double-differential feeding using two identical 3 dB/180° ring hybrid couplers with nice amplitude and phase balance effectively suppresses the interport RF leakage to achieve very high isolation. The prototype of the proposed antenna architecture is implemented using a 1.6 mm thick general-purpose FR-4 substrate. The implemented antenna provides more than 90 and 80 dB interport RF isolation for 20 and 40 MHz bandwidths, respectively, in addition to more than 98 dB port-to-port peak isolation when measured inside an anechoic chamber. To the best of our knowledge, this is the highest amount of RF isolation reported for a single dual-polarized patch antenna.

Circularly Polarized Implantable Antenna for 915 MHz ISM-Band Far-Field Wireless Power Transmission

Abstract: A wireless power link with circular polarization is studied in this letter for far-field wireless power transmission. First, a miniaturized circularly polarized (CP) implantable antenna is designed at 915 ISM band. The proposed antenna features a good miniaturization with the dimensions of 11 × 11 × 1.27 mm3 by employing the stub loading and capacitive coupling among the stubs. It has the smallest size and maintains good radiation performance, compared with previous CP implantable antennas. The simulated impedance bandwidth covers from 889 to 924 MHz for | S 11| less than −10 dB, and the axial-ratio (AR) bandwidth (AR < 3 dB) is from 901 to 912 MHz. The results show that the antenna is suitable for far-field wireless power transmission. The proposed wireless power link achieves higher converted dc power compared to previous similar letter.

Transmit Beampattern Synthesis for the FDA Radar

Abstract: The frequency diverse array (FDA) radar has drawn great attention due to the periodicity of the beampattern in range, angle, and time. In this letter, we restudy the recent work that designed a time-invariant beampattern of the FDA radar, which can focus the transmit energy in a desired position. We reanalyze the derivation of the FDA beampattern synthesis and point out the neglected constraint condition, which leads the research of the FDA beampattern synthesis to an impractical direction. By comparing the replication of one of the prior works with our result, we draw a conclusion that it is impossible to obtain a beampattern merely focusing on some specific spatial positions and lasting for some specific time.

Design of a Broadband Polarization-Reconfigurable Fabry–Perot Resonator Antenna

Abstract: In this letter, a broadband polarization-reconfigurable Fabry–Perot (FP) resonator antenna is presented for WLAN/WiMAX applications. The open air-filled FP cavity is constructed by a partially reflective surface (PRS) layer directly placed over a fully reflective ground plane. A two-element patch array is employed to serve as a feeder. To achieve polarization reconfigurability, the feeding antenna is designed to have the capability of switching between horizontal linear polarization (HP) and vertical linear polarization (VP) by controlling the on/off states of four pairs of p-i-n diodes. By combining the frequency resonances of the FP cavity and the feeding antenna, the proposed FP resonator antenna obtains broadband performance. Furthermore, the proposed antenna achieves a broadband 3 dB gain bandwidth by designing the PRS layer to have a reflection phase with positive slope over as wide a frequency band as possible. The proposed antenna was fabricated and experimentally characterized. Measurements demonstrate that it achieves a −10 dB impedance bandwidth of 21 $\%$ ranging from 2.2 to 2.72 GHz, which can well cover WLAN/WiMAX band of operation. The 3 dB gain bandwidths of 12.5 $\%$ and 14.6 $\%$ are obtained with peak realized gains of 15.1 and 14.8 dBi for the HP and VP, respectively.

Double-Layer Circuit Analog Absorbers Based on Resistor-Loaded Square-Loop Arrays

Abstract: Based on the equivalent circuit model, it is demonstrated that five resonances can occur within the absorption band of a circuit analog absorber containing two lossy layers. The lossy layers are composed of resistor-loaded square-loop and double-square-loop arrays. In the absence of a dielectric skin, an initial design with four resonances observed from its reflectivity exhibits a simulated bandwidth ratio (BWR) of 1:8.45 for at least 10 dB absorption. To facilitate physical implementation of the wideband absorber, a modified design is proposed to compensate the effect of parasitic parameters of actual resistors on reflectivity. It is shown through measurement that an operating BWR of 1:8.78 is achieved with the reflectivity smaller than −10 dB under normal incidence. The total thickness of the absorber prototype is only 0.096 λ at the lowest operating frequency. The agreement between simulation and measurement validates the proposed design.

A Compact Broadband Dual-Polarized Antenna Array for Base Stations

Abstract: A compact $\pm \text{45}^{\circ }$ dual-polarized broadband antenna array is proposed in this letter for base stations. For the sake of structural simplicity, low profile, and ease of mass production, printed dipoles are adopted as the dual-polarized antenna element. To achieve the broadband performance, radiators are designed to be spline-edged bowties, and they are fed by tapered transmission lines. Moreover, to improve the symmetry and stability of the radiation pattern, the Pawsey stub baluns are used to balance the antenna structure. Finally, an eight-element antenna array prototype backed by a folded reflector is fabricated and measured. The compact antenna array has a broad bandwidth of 68% (1.427–2.9 GHz) with a voltage standing-wave ratio less than 1.5 and stable radiation properties to provide international mobile telecommunication services over 2G/3G/LTE systems and L- and S -bands released recently.

Low-Profile and Wideband Microstrip Antenna With Stable Gain for 5G Wireless Applications

Abstract: A low-profile microstrip antenna with stable radiation pattern in a relatively wide band is presented for 5G operation. Four resonant modes with different frequencies are integrated in a single structure to enhance the bandwidth with stable gain, and well matched by introducing the folded walls. An impedance bandwidth of 58.3% has been achieved from 2.84 to 5.17 GHz with a compact structure of ${\text{0.84}}\lambda _{0}\,\times \,{\text{0.68}}\lambda _{0}\,\times \,{\text{0.06}}\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the center frequency of 4 GHz. The measurement results show that the proposed antenna is with the merits of average gain of 5 dBi, stable radiation patterns, low cross polarization, and low backlobes, exhibiting potentially use for the applications of 5G wireless communication systems.

Stacked Microstrip Linear Array for Millimeter-Wave 5G Baseband Communication

Abstract: A 42-element microstrip parasitic patch antenna is developed in the millimeter-wave band for fifth-generation mobile communication base stations. A metalized elliptical stripline-to-embedded-microstrip transition with adaptive via-hole arrangement as well as a 20 dB Chebyshev tapered six-way power divider is proposed to have an insertion loss of 0.045 dB. To confirm the feasibility of the antenna, it has been measured to provide a 6.3% fractional bandwidth from 26.83 to 28.56 GHz at VSWR of less than 1.96. The array antenna gains of more than 21.4 dBi have been realized with sidelobe levels of better than –19.1 dB, operating within 27.5–28.5 GHz in both the azimuth and elevation directions.

Low-Profile Spoof Surface Plasmon Polaritons Traveling-Wave Antenna for Near-Endfire Radiation

Abstract: This letter proposes a low-profile and highly efficient endfire radiating traveling-wave antenna based on spoof surface plasmon polaritons (SSPPs) transmission line. The aperture is approximately $0.32\lambda _0\times 0.01\lambda _0$ , where $\lambda _0$ is the space wavelength at the operational frequency 8 GHz. This antenna generates near-endfire radiation beams within 7.5–8.5 GHz. The maximum gain and total efficiency reach 9.2 dBi and $96\%$ , respectively. Measurement results are finally given to validate the proposed SSPPs antenna.

Low-Profile Dual-Polarization Frequency-Selective Rasorbers Based on Simple-Structure Lossy Cross-Frame Elements

Abstract: The low-profile dual-polarization frequency-selective rasorbers with very simple structures are investigated. Based on an equivalent circuit model, the operating principle and design method are first studied. One rasorber using lossy cross-frame elements and double-square loops is then proposed, which exhibits two absorption bands at the two sides of one passband. Moreover, the rasorbers with reduced cell size are further developed to stabilize the angular response. Under normal incidence, an insertion loss of about 0.26 dB is obtained at 4.25 GHz, the fractional bandwidth for reflection less than −10 dB is over 100%, and the thickness is around ${\text{0.1}}\,\lambda _{L}$ . For demonstration, the rasorber prototypes are fabricated and measured, while reasonable agreements are observed accordingly.