Showing papers in "IEEE Transactions on Antennas and Propagation in 2018"
TL;DR: A framework of the deep neural network to address the DOA estimation problem, so as to obtain good adaptation to array imperfections and enhanced generalization to unseen scenarios andSimulations are carried out to show that the proposed method performs satisfyingly in both generalization and imperfection adaptation.
Abstract: Lacking of adaptation to various array imperfections is an open problem for most high-precision direction-of-arrival (DOA) estimation methods. Machine learning-based methods are data-driven, they do not rely on prior assumptions about array geometries, and are expected to adapt better to array imperfections when compared with model-based counterparts. This paper introduces a framework of the deep neural network to address the DOA estimation problem, so as to obtain good adaptation to array imperfections and enhanced generalization to unseen scenarios. The framework consists of a multitask autoencoder and a series of parallel multilayer classifiers. The autoencoder acts like a group of spatial filters, it decomposes the input into multiple components in different spatial subregions. These components thus have more concentrated distributions than the original input, which helps to reduce the burden of generalization for subsequent DOA estimation classifiers. The classifiers follow a one-versus-all classification guideline to determine if there are signal components near preseted directional grids, and the classification results are concatenated to reconstruct a spatial spectrum and estimate signal directions. Simulations are carried out to show that the proposed method performs satisfyingly in both generalization and imperfection adaptation.
302 citations
TL;DR: In this article, a novel frequency-selective rasorber (FSR) is proposed, which has a nearly transparent window between two absorption bands, and the insertion loss of FSR at the resonant frequency of lossless bandpass FSS is proven to be only related to the equivalent impedance of the resistive sheet.
Abstract: A novel frequency-selective rasorber (FSR) is proposed in this paper which has a nearly transparent window between two absorption bands. The FSR consists of a resistive sheet and a bandpass frequency-selective surface (FSS). The impedance conditions of absorption/transmission for both the resistive sheet and the bandpass FSS are theoretically derived based on equivalent circuit analysis. The insertion loss of FSR at the resonant frequency of lossless bandpass FSS is proven to be only related to the equivalent impedance of the resistive sheet. When the resistive sheet is in parallel resonance at the passband, a nearly transparent window can be achieved regardless of lossy properties. An interdigital resonator (IR) is designed to realize parallel resonance in the resistive element by extending one finger of a strip-type interdigital capacitor to connect the two separate parts of the capacitor. The IR is equivalent to a parallel LC circuit. Lumped resistors are loaded around the IR to absorb the incident wave at lower and upper absorption bands. With the bandpass FSS as the ground plane, the absorption performances at both the lower and upper bands around the resonant frequency are improved compared to a metal-plane-backed absorber structure. The FSR passband is designed at 10 GHz with an insertion loss of 0.2 dB. The band with a reflection coefficient below −10 dB extends from 4.8 to 15.5 GHz. A further extension to dual-polarized FSR is designed, fabricated, and measured to validate the proposed design.
215 citations
TL;DR: In this article, a compact design of multiple-input multiple-output (MIMO) Antenna with dual sharply rejected notch bands for portable wireless ultrawideband (UWB) applications is presented and experimentally investigated.
Abstract: In this paper, a compact design of multiple-input multiple-output (MIMO) Antenna with dual sharply rejected notch bands for portable wireless ultrawideband (UWB) applications is presented and experimentally investigated. The proposed UWB MIMO Antenna has a compact size of 18 mm $\times$ 34 mm. The tapered microstrip fed slot Antenna acts as a single radiating element with inverted L-shaped slits to introduce notches at wireless local area network and the IEEE INSAT/Super-Extended C-bands. The mutual coupling of less than −22 dB is achieved over the entire operating band (2.93–20 GHz). At the center of notched band, the efficiency of the Antenna drops that indicates a good interference suppression performance. The performance of the MIMO Antenna in terms of isolation among the ports, radiation pattern, efficiency, realized gain, envelope correlation coefficient, mean effective gain, and total active reflection coefficient is studied.
213 citations
TL;DR: The design of a novel practical 28 GHz beam steering phased array antenna for future fifth generation mobile device applications is presented and the impacts of user’s hand effects are investigated.
Abstract: The design of a novel practical 28 GHz beam steering phased array antenna for future fifth generation mobile device applications is presented in this communication. The proposed array antenna has 16 cavity-backed slot antenna elements that are implemented via the metallic back casing of the mobile device, in which two eight-element phased arrays are built on the left- and right-side edges of the mobile device. Each eight-element phased array can yield beam steering at broadside and gain of >15 dBi can be achieved at boresight. The measured 10 dB return loss bandwidth of the proposed cavity-backed slot antenna element was approximately 27.5–30 GHz. In addition, the impacts of user’s hand effects are also investigated.
209 citations
TL;DR: The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure and provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance.
Abstract: In this communication, the novel compact tightly arranged pairs are employed to form a $4 \times 4$ multiple-input-multiple-output (MIMO) system and an $8 \times 8$ MIMO system operating at 3.4–3.6 GHz for fifth-generation (5G) mobile phones. Each tightly arranged pair is composed of a bent monopole and an edge-fed dipole with a compact size of $7 \times 12$ mm2. The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure. With the help of the orthogonal mode, isolation performances across the desired band of the $4 \times 4$ MIMO system and the $8 \times 8$ MIMO system are better than 20 and 17 dB, respectively, with the elements closely spaced. The measured efficiencies are 51.7%–84.5%/49%–72.9%, and the measured envelope correlation coefficients are less than 0.06/0.07 for the $4 \times 4/ 8 \times 8$ MIMO system. The proposed MIMO systems provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance.
192 citations
TL;DR: In this paper, an eight-port antenna array operating in 3.5 GHz band and 5 GHz band for 5G MIMO in mobile handsets is presented, and the measured results have exhibited good impedance matching and isolation.
Abstract: An eight-port antenna array operating in 3.5 GHz band (3400–3600 MHz) and 5 GHz band (4800–5100 MHz) for fifth-generation multiple-input multiple-output (MIMO) in mobile handsets is presented. To reserve space for 2G/3G/4G antenna configuration, the eight-antenna array formed by two quad-antenna arrays is printed along the two long frames of the smartphone. Each antenna array unit is formed by a folded monopole and a gap-coupled loop branch, and they are disposed on the upper and bottom sides of the system circuit board, respectively. As the gap between each array unit is only 10 mm, a neutralized line is introduced between the two middle antenna units for reducing the mutual coupling. The measured results have exhibited good impedance matching and isolation. To evaluate the MIMO performance, the envelope correlation coefficient, mean effective gain, and ergodic channel capacity are investigated. Furthermore, the hand phantom effects and display panel effects are also given.
181 citations
TL;DR: In this paper, a filtering antenna based on the filtering-radiating patch (FRP) is proposed, where two radiation nulls are realized at both band edges of the antenna efficiency curve, leading to a sharp band skirt and good selectivity in the boresight gain response.
Abstract: This communication demonstrates a method to design filtering antennas by using the filtering-radiating patch (FRP). The so-called FRP is a structure of a rectangular patch etched with slots. It inherits the radiation performance of conventional patch antennas, and more importantly, introduces filtering feature with a radiation null at either the upper or lower band edge of radiation efficiency curve. The frequencies of radiation nulls are easy to control. Based on the FRP, a novel filtering antenna is proposed. Two radiation nulls are realized at both band edges of the antenna efficiency curve, leading to a sharp band skirt and good selectivity in the boresight gain response. The locations of the two radiation nulls can be flexibly controlled by the lengths of slots. A prototype is fabricated and tested. The measured results show an impedance matching bandwidth of 7% with a center frequency of 5.24 GHz, two radiation nulls at 4.7 and 5.85 GHz, respectively, a realized gain of 6.6 dBi, the cross-polarization rejection larger than 23.4 dB, and the front-to-back ratio better than 15 dB. The presented method demonstrates the capability of not only achieving good filtering-radiating performances but also possessing very simple structures by only etching slots on the patch of a conventional microstrip antenna.
177 citations
TL;DR: In this article, a broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed.
Abstract: A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband $4\times 4$ SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications.
154 citations
TL;DR: In this article, a Ka-band inset-fed microstrip patches linear antenna array is presented for 5G applications in different countries, which employs 16 elements in an H-plane new configuration.
Abstract: 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° rotating sequence to decrease the mutual coupling and improve the radiation pattern symmetry. A (24.4%) measured bandwidth (24.35–31.13 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. These characteristics are in good agreement with the simulations, rendering the antenna to be a good candidate for 5G applications.
154 citations
TL;DR: In this paper, a compact metasurface-based antenna for dual-band operations is proposed on a single-layered substrate including an array of modified $3 \times 3$ squared patches, each of the four corner patches is split into four fractional patches while the four edge patches are evolved into Malta crosses and the center patch is scaled.
Abstract: A compact metasurface-based antenna is proposed for dual-band operations. The proposed metasurface is designed on a single-layered substrate including an array of modified $3 \times 3$ squared patches. Each of the four corner patches is split into four fractional patches while the four edge patches are evolved into Malta crosses and the center patch is scaled. A substrate integrated waveguide-based Y-junction cavity-fed dual slot drives the metasurface with multiple impedance resonances. Based on the predicted modal behaviors of metasurface using a characteristic mode analysis (CMA), as an example, an antenna operating at three resonant modes at 28, 33, and 36 GHz, respectively is designed for the dual-band operation for the coming 5G. The proposed design shows that the measured impedance bandwidths (return loss larger than 10 dB) are 23.7–29.2 GHz and 36.7–41.1 GHz with the achieved gain of 4.8–7.2 dBi and 8.9–10.9 dBi, respectively. The proposed dual-band antenna features the advantages of low profile and wideband, suitable for the coming dual-band 5G applications.
151 citations
TL;DR: In this article, an active metasurface composed of butterfly-shaped unit cells embedded with voltage-controlled varactor diodes was proposed to adaptively switch among linear-to-linear, linear to linear, linearto-elliptical, and linear to circular polarization conversions in a wideband.
Abstract: We propose an active metasurface whose functionalities can be dynamically switched among linear-to-linear, linear-to-elliptical, and linear-to-circular polarization conversions in a wideband. The active metasurface is composed of butterfly-shaped unit cells embedded with voltage-controlled varactor diodes. By controlling the bias voltage of the varactor diodes, the electromagnetic responses of the proposed metasurface can be tailored, leading to reconfigurable polarization conversions. The simulation results reveal that with no bias voltage, the proposed metasurface is able to reflect linear-polarization waves to cross-polarization waves in the frequency range from 3.9 to 7.9 GHz, with a polarization conversion ratio of over 80%; however, at the bias voltage of −19 V, the metasurface is tuned to be a circular polarization converter in a wideband from 4.9 to 8.2 GHz. Moreover, two equivalent circuits along the $x$ - and $y$ -directions are developed to elucidate the tunable mechanism. The experimental results are in a good agreement with the simulation results obtained from commercial software and from the equivalent circuit model.
TL;DR: In this article, a medium-based approach based on generalized sheet transition conditions and surface susceptibility tensors is proposed to obtain diffraction-free refractive metasurfaces that are essentially lossless, passive, bianisotropic, and reciprocal.
Abstract: Refraction represents one of the most fundamental operations that may be performed by a metasurface. However, simple phase-gradient metasurface designs suffer from restricted angular deflection due to spurious diffraction orders. It has been recently shown, using a circuit-based approach, that refraction without spurious diffraction, or diffraction-free, can fortunately be achieved by a transverse (or in-plane polarizable) metasurface exhibiting either loss–gain, nonreciprocity, or bianisotropy. Here, we re-derive these conditions using a medium-based—and hence, more insightful—approach based on generalized sheet transition conditions and surface susceptibility tensors, and experimentally demonstrate for the first time, beyond any doubt, two diffraction-free refractive metasurfaces that are essentially lossless, passive, bianisotropic, and reciprocal.
TL;DR: In this paper, a planar ultrawideband modular antenna (PUMA) array is proposed to mitigate low-frequency bandwidth-limiting loop modes and shift problematic common-mode resonances out-of-band.
Abstract: The theory, design, fabrication, and measurement of a new class of planar ultrawideband modular antenna (PUMA) arrays are presented. The proposed PUMA array class achieves twice the bandwidth (from 3:1 to 6:1) of the conventional shorted via-based PUMA without using an external matching network and while retaining convenient unbalanced feeding, manufacturing, and assembly characteristics. The chief enabling technical innovation hinges upon the reconfiguration of shorting vias into capacitively-loaded vias that simultaneously: 1) mitigate low-frequency bandwidth-limiting loop modes and 2) shift problematic common-mode resonances out-of-band. A simple theoretical model based on ridged waveguides is proposed that qualitatively and quantitatively explains this novel common-mode mitigation. An infinite array operating over 3.53–21.2 GHz (6:1) is designed to achieve active VSWR < {2, 2.5, 3.8} while scanning to {broadside, 45°, 60°}, respectively, without oversampling the aperture. D-plane cross-polarization is around {−15, −10} dB for {45°, 60°} scans with high efficiency, i.e., 0.5 dB co-polarized gain loss on average. A dual-polarized prototype 256-port (128 elements per polarization) array is fabricated and measured having good agreement with full-wave finite array simulations.
TL;DR: In this article, a dual-band dual-linear polarization (LP)-to-CP converter is proposed for satellite communications at 19.7-20.2 GHz and 29.5-30 GHz.
Abstract: Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications, the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm $\times5.3$ mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer.
TL;DR: In this paper, a chessboard arranged metamaterial superstrate (CAMS) is used to enhance the antenna gain and reduce the radar cross-section (RCS) of a Fabry-Perot (FP) resonator antenna.
Abstract: The simultaneous improvement in radiation and scattering performance of an antenna is normally considered as contradictory. In this paper, wideband gain enhancement and radar cross section (RCS) reduction of Fabry–Perot (FP) resonator antenna are both achieved by using chessboard arranged metamaterial superstrate (CAMS). The CAMS is formed by two kinds of frequency-selective surfaces. The upper surface of CAMS is designed to reduce RCS based on the phase cancellation principle, and the bottom surface is used to enhance antenna gain on the basis of FP resonator cavity theory. Both simulation and measured results indicate that compared with primary antenna, the gain of the proposed FP resonator antenna is enhanced by 4.9 dB at 10.8 GHz and the 3 dB gain bandwidth is from 9.4 to 11.1 GHz (16.58%). Meanwhile, the RCS of the proposed FP resonator antenna is reduced from 8 to 18 GHz, with peak reduction of 39.4 dB. The 10 dB RCS reduction is obtained almost from 9.6 to 16.9 GHz (55.09%) for arbitrary polarizations. Moreover, the in-band RCS is greatly reduced, owing to the combined effect of CAMS and FP resonator cavity.
TL;DR: The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size, and the overall RF-to-dc efficiency of the multiport pixel rectenna is shown to be 19% when the total input RF power is −20 dBm.
Abstract: We describe the design of a multiport pixel rectenna for ambient radio-frequency (RF) energy harvesting consisting of an optimized triple-port pixel antenna and a triple-port rectifier with dc combining. The advantages of the multiport pixel approach include enhanced harvested RF power for a given area as well as a reduction in the antenna matching requirements. We formulate the design of the triple-port pixel antenna as a binary optimization problem with an objective function related to harvested RF power in the GSM-1800 band for specified power angular spectrums without the need for antenna matching components. The optimization of the triple-port pixel antenna is obtained by using successive exhaustive Boolean optimization. The design for the triple-port rectifier with dc combining is also provided and a prototype is demonstrated. The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size. The overall RF-to-dc efficiency of the multiport pixel rectenna is also evaluated and shown to be 19% when the total input RF power is −20 dBm. The effects of nonuniformity in the input RF power across antenna ports are also investigated.
TL;DR: In this paper, a method is proposed to suppress the unwanted higher order modes (HOMs) of the metasurfaces in multiport antenna systems for improving the radiation performances using characteristic mode analysis (CMA).
Abstract: A method is proposed to suppress the unwanted higher order modes (HOMs) of the metasurfaces in multiport antenna systems for improving the radiation performances using characteristic mode analysis (CMA). The proposed method is to control the modal currents under consideration by loading the unit cells of the metasurface with slots and vias. The positions of loads are determined with the aid of CMA of the metasurface. For proof of concept, the proposed technique is applied to a compact wideband four metasurface antenna (MA) systems operating at 5 GHz Wi-Fi bands. With the suppression of HOMs, the split and tilted radiation patterns of the MAs are significantly improved. The concept is experimentally validated for potential compact multiport antenna applications.
TL;DR: In this article, a fully metallic Luneburg lens was proposed to produce a link between 3-D homogeneous surfaces and 2-D dielectric lenses where the propagation is only in the air.
Abstract: Non-Euclidean transformations have been recently proposed to produce a link between 3-D homogeneous surfaces and 2-D dielectric lenses. Therefore, the propagation in a geometrical surface has the same response of an equivalent refractive index distribution. By using this concept, we propose here a fully metallic Luneburg lens where the propagation is only in the air. Two metallic plates, following a curved shape, are employed to support the propagation mimicking the designed curvature. To reduce the height of the required curvature, the surface has been mirrored twice with respect to two $z$ constant planes. The lens is fed by 11 waveguide ports spaced with an angle of 12.5° providing 1-D beam scanning over an angular range of ±62.5°. A prototype is manufactured and measured with a good agreement with the simulated results between 25 and 36 GHz to demonstrate the concept.
TL;DR: In this article, a low profile dual-polarized dipole antenna using wideband artificial magnetic conductor (AMC) reflector with stable radiation pattern for use in 2G/3G/4G base stations operating from 1.7 to 2.7 GHz is presented.
Abstract: A low-profile dual-polarized dipole antenna using wideband artificial magnetic conductor (AMC) reflector with stable radiation pattern for use in 2G/3G/4G base stations operating from 1.7 to 2.7 GHz is presented. The antenna consists of a pair of crossed-dipoles and a wideband AMC reflector which consists of an AMC surface, a metallic ground plane, and the air substrate between them. The AMC is designed to operate with 90° reflection-phase bandwidth of 1.64–2.88 GHz (54.8%). Compared with using perfect electric conductor reflector, the profile height of the dual-polarized dipole antenna using AMC reflector is reduced by half from 36 to 18 mm, resulting in the lowest-profile 2G/3G/4G base station antenna. Six metallic ground walls are used to stabilize the radiation pattern, and the resulted half-power beamwidths are around 68±3° and 81±3° in the H- and V-planes, respectively, across the operating band. More measured results show that wide impedance bandwidths of 1.67–2.98 and 1.64–3.05 GHz for the two input ports, isolation of more than 25 dB, and cross-polarization of less than −20 dB are achieved.
TL;DR: In this paper, a flexible dual-band antenna with a metamaterial structure (MS) is presented, which makes the antenna thin and bendable, is used as the substrate for the antenna.
Abstract: A flexible dual-band antenna with a metamaterial structure (MS) is presented. Polyimide substance, which makes the antenna thin and bendable, is used as the substrate for the antenna. When the MS is placed between the antenna and the human’s forearm, the antenna gain is increased by 9.3 and 5.37 dB, and the radiation efficiency is increased by 48.4% and 35.7%, at 2.45 and 5.8 GHz, respectively. In addition, the specific absorption rate is decreased by more than 70%, considering the limitations imposed by Federal Communications Commission and the regulation of International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the frequencies cited above. The fabricated prototype of the antenna with the integrated MS was investigated by placing it on different places of human body, as also on different human bodies. The obtained results show that the proposed antenna is safe and suitable for use, in terms of the ICNIRP standards of World Health Organization.
TL;DR: In this paper, a simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but non-identical elements per unit cell.
Abstract: A simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but nonidentical elements per unit cell. With the technique, one needs only to optimize the distance between the two elements and the dimension of the second element, starting with a quarter of the period and the dimension of the first element. With the simple design procedure, the technique is practical and effective for the open-stopband suppression for various periodic leaky-wave antennas. Two periodic leaky-wave antennas with the technique are demonstrated. The first one is a new developed substrate-integrated waveguide antenna with two nonidentical transverse slots per unit cell. The antenna has a wide scanning range from the backward endfire to the forward direction and does not suffer from blind scanning points at endfires (if it is placed on an infinite ground plane). The antenna is theoretically investigated. The simulation and measured results are consistent with the theoretical results. The second one is a microstrip combline leaky-wave antenna, in which each unit cell contains two nonidentical open-ended stubs. The two examples validate that the technique proposed in this paper can completely eliminate the open stopband in periodic leaky-wave antennas.
TL;DR: In this article, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for beam scanning and multibeam applications at X-bands.
Abstract: Based on a transformation optics method, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for beamscanning and multibeam applications at X-bands. The transformed material properties of the planar Luneburg lens are designed with 17-layered permittivity distribution of polynomials. Each layer is discretized into $41 \times 41$ pixels made of broadband and less polarization-dependent unit cells responsible for desired index distributions. The effects of transformation, approximation, and discretization on the lens performance are analyzed comprehensively. Also, to validate the implementation method, a flat Luneburg lens with a thickness of 14.1 mm, a focal length of 28 mm, and an aperture size of $98.9 \times 98.9$ mm2 is designed and tested. A stacked aperture-coupled patch antenna operating at 10 GHz is applied as a feeder. The measured results show that the proposed antenna can operate over a bandwidth of ~20% with an antenna efficiency of 32%, a cross-polarization level of <−17.1 dB, as well as the maximum gain of 15.9/16.35 dBi and a scanning angle of ±32°/±35° for two orthogonal polarizations, respectively. The presented flat Luneburg lens antenna featuring broad bandwidth, high gain, wide scanning angle, and easy fabrication has a high potential in 5G wireless communication, imaging, and remote sensing applications.
TL;DR: In this paper, the authors proposed a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure, which is introduced by etching periodical slots on the top surface of SIW.
Abstract: In this communication, we propose a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure. The slow-wave effect is introduced by etching periodical slots on the top surface of SIW. The LWA radiation is subsequently realized by introducing sinusoidal modulation to the slots profile. Such a structure significantly improves the scanning rate of LWA due to the small group velocity at the slow-wave region. Simulation and measured results indicate that the proposed LWA scans a wide angle in a narrow bandwidth near the cutoff frequency of surface plasmon polariton. Within the frequency band 13.5–13.9 GHz (3% relative bandwidth), the measured scanning angle is from 2° to 37° with the measured gain all above 9.2 dBi.
TL;DR: In this article, a broadband dual-polarized filtering dipole antenna for base station application is presented, which consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops.
Abstract: This paper presents a broadband dual-polarized filtering dipole antenna for base-station application, which has a compact size of 50 $\text {mm} \times 50\,\,\text {mm} \times 31.8$ mm. The antenna consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops. Without using complex filtering circuits, the dual-polarized dipole antenna realizes satisfactory filtering performance and enhanced bandwidth by employing only two parasitic loops. Two specific radiation nulls are thus generated and individually controlled by the two parasitic loops. To further improve the upper stopband selectivity and bandwidth, a simple open-ended stub is added to the arms of the dipole. As a result, the bandwidth can be tuned from 7.4% to 47.6%, and the realized gain is decreased dramatically from 8.6 dBi at 2.7 GHz (in-band) to −10 dBi at 2.9 GHz (out-of-band). For demonstration, a broadband dual-polarized dipole antenna is implemented. Measured results show that the proposed antenna has more than 34 dB port isolation over 48.7% (1.66–2.73 GHz) impendence bandwidth (VSWR < 1.5). The measured in-band gain is about 8.15 dBi with stable 3 dB beamwidth 65.4°±2.4° in the horizontal plane, whereas the out-of-band radiation suppression is more than 17 dB.
TL;DR: In this article, an electronically controllable microstrip leaky-wave antenna (LWA) is proposed to steer the radiations at a fixed frequency, which is composed of a corrugated microstrip line loaded by the varactor diodes with triangular-modulated surface impedance.
Abstract: An electronically controllable microstrip leaky-wave antenna (LWA) to steer the radiations at a fixed frequency is presented. The proposed LWA is composed of a corrugated microstrip line loaded by the varactor diodes with triangular-modulated surface impedance. Due to the periodical modulation of the surface impedance, the guided waves can be converted into the leaky-wave radiations efficiently with frequency-scanning property. Furthermore, the surface impedance of the LWA can be reconfigured by changing the capacitance of the varactor diode through dc bias voltage, which will make the radiation beam steer in a large angle range accordingly at a fixed frequency. Both numerical simulations and experimental results show that the radiation beams can be controlled for continuously steering at each frequency from 5.5 to 5.8 GHz by changing the dc bias voltage from 0 to 20 V, in which the scanning angle can reach as high as 45°.
TL;DR: In this paper, the authors proposed a novel antenna system that combines the functionalities of TAs and RAs, which consists of a specially designed bifunctional metalens and a self-made Vivaldi antenna (feed source).
Abstract: The use of microstrip transmitarrays (TAs) and reflectarrays (RAs) is essential in long-range communication systems because of their high-gain radiations, narrow beam widths, simple configurations, and easy fabrication. We propose a novel antenna system that combines the functionalities of TAs and RAs. The antenna system consists of a specially designed bifunctional metalens and a self-made Vivaldi antenna (feed source). The metalens can focus the y-polarized incident wave at the transmission side and focus the x-polarized wave at the reflection side with the same focal length. By launching the metalens with differently polarized Vivaldi antennas, we were able to obtain a TA and RA. Moreover, the realized RA can deflect the radiation beam to a specified angle to avoid blockage of the feed antenna. Our numerical and experimental results coincided, indicating that the proposed antenna system demonstrated several improvements, including the ability to achieve multiradiation patterns, realize high gains, and adopt simple standard print circuit board technology. Our findings significantly expand the capabilities of metasurfaces in controlling electromagnetic waves and open up a new avenue for the design of high-performance multifunctional antenna systems and metadevices.
TL;DR: In this article, the authors presented a novel method of decoupling inverted-F antennas (IFAs) with high-order modes of a ground plane in 5G mobile multiple-input multiple-output (MIMO) platform.
Abstract: This paper presents a novel method of decoupling inverted-F antennas (IFAs) with high-order modes of a ground plane in 5G mobile multiple-input multiple-output (MIMO) platform. The proposed method is illustrated in a dual-antenna 5G mobile platform operating at 3.5 GHz. An IFA excites a high-order mode of the field distribution in the ground plane at 3.5 GHz. The electric field of the excited high-order mode forms several stable null-amplitude field points located on the edge of the ground plane. The other IFA is then placed in one of the stable null points. By doing this, the two IFAs are decoupled with high isolation. The simulated results show that isolation improvements of 20–40 dB can be achieved when the positions and orientations of the two IFAs are optimized. The measured results confirm that the fabricated antennas have peak isolations of 45–56 dB. Finally, the proposed method is applied to design a three-IFA-based MIMO platform which verifies that the suggested concept can effectively simplify the decoupling mechanism and works well in a multiantenna-based mobile MIMO terminal.
TL;DR: In this paper, phase and amplitude control reflected metasurface (MS) antennas have been proposed to simultaneously manipulate the antenna's main lobe and sidelobes, achieving a high gain of 20.7 dB at 10 GHz.
Abstract: The metasurface (MS) antenna is an important microwave component in the communication system due to its unique beam radiation capability. However, current studies mainly pay attention to improve the performance of the main lobe of the MS antenna, leaving the sidelobe unexplored although it is also essential in some practical applications. In this paper, several phase- and amplitude-control reflected MSs have been proposed to simultaneously manipulate the antenna’s main lobe and sidelobes. The MSs consist of modified I-shaped particles which can independently manipulate the phases and amplitudes of the cross-polarization waves by changing the split size and orientation, respectively. A focusing phase distribution and different Taylor amplitude distributions have been fixed on the MSs. By illuminating the MSs with a self-made antenna, we have successfully designed four MS antennas. For the first antenna, we solely pay attention to improve the main lobe and achieve a high gain of 20.7 dB at 10 GHz. For the other three antennas, we also aim to manipulate their sidelobes. The resultant sidelobe levels (SLLs) are about −25 dB in the $xoz$ plane for the second antenna, −29 dB in the $yoz$ plane for the third antenna, and both of the former two characteristics for the fourth antenna. Compared with the first MS antenna, the last three antennas suffer from gain reductions of 2, 1.7, and 3 dB, respectively. These proposed MS antennas provide a new way to manipulate both main-lobe levels and SLLs and also greatly promote the integration of MSs and antennas.
TL;DR: In this article, a planar millimeter-wave 2D beam-scanning multibeam array antenna fed by compact 16-way beamforming network (BFN) in multilayered substrate integrated waveguide (SIW) technology is addressed.
Abstract: A planar millimeter-wave 2-D beam-scanning multibeam array antenna fed by compact 16-way beam-forming network (BFN) in multilayered substrate integrated waveguide (SIW) technology is addressed. The BFN is formed by connecting two stacks of sub-BFNs, the E-plane sub-BFN and the H-plane sub-BFN. The H-plane sub-BFN is realized by a traditional H-plane $4 \times 4$ Butler matrix (BM). The key point of this design is to propose an E-plane $4 \times 4$ BM which realizes a planar E-plane sub-BFN. These two sets of sub-BFNs can joint directly without resorting to any connectors or connecting networks to form such a compact 16-way BFN with a reduced area of merely $3\lambda \times 12\lambda $ . After that, to be compatible with the proposed BFN, a ladder-type $4 \times 4$ slot antenna array is employed, which is comprised of four linear $1 \times 4$ slot antenna arrays. Different from traditional array, the four subarrays are distributed in separate layers for the purpose of jointing to the BFN more conveniently. Transition network are also required to connect the BFN with the antenna array. Finally, a compact 2-D scanning multibeam array antenna based on the planar SIW BFN are fabricated and measured, which would be an attractive candidate for 5G application.
TL;DR: In this article, a triple band differential rectenna for RF energy harvesting applications is proposed, which is designed to operate in frequency bands of universal mobile telecommunication service (2.1 GHz), lower WLAN/Wi-Fi (2, 2.48 GHz), and WiMAX (3.3-3.8 GHz).
Abstract: A triple band differential rectenna for RF energy harvesting applications is proposed in this paper. The rectenna is designed to operate in frequency bands of universal mobile telecommunication service (2.1 GHz), lower WLAN/Wi-Fi (2.4–2.48 GHz), and WiMAX (3.3–3.8 GHz). For designing the proposed rectenna, first a differentially fed multiband slot antenna that works as the front-end receiving unit is designed, fabricated, and tested to check its performance. It is observed that a peak antenna gain of 7, 5.5, and 9.2 dBi is achieved at 2, 2.5, and 3.5 GHz, respectively. In the next step, a triple band differential rectifier is designed using the Villard voltage doubler where interdigital capacitors (IDCs) in lieu of lumped components are used. The full rectifier circuit comprising of the rectifying unit and impedance matching circuit is fabricated and tested to check its performance in the desired bands. The peak RF-dc conversion efficiency of 68% is obtained using the three-tone measurement. In the final stage, both antenna and the rectifier circuit are integrated through SMA connecter in order to implement the proposed rectenna. Measurement of the proposed rectenna shows an approximate maximum efficiency of 53% at 2 GHz, 31% at 2.5 GHz, and 15.56% at 3.5 GHz.