Search

A wideband transmitarray antenna based on the magnetoelectric (ME) dipole element and 2-bit phase compensation scheme is presented for vehicular communications in this paper. A wideband 90° phase shifter is proposed and combined with the rotating method to achieve four discrete phase states. Thanks to the polarization-twisting technique and the simple structure of the phase shifter, the proposed element can be easily designed. For the transmitarray design, a multi-frequency phase compensation strategy is applied to guarantee stable performance over the operating band. To validate the design, a 12 × 12 transmitarray antenna simultaneously covering vehicle-to-satellite band (20 GHz), and 5G millimeter-wave (mmWave) bands (24 GHz/28 GHz) is designed, fabricated and measured. The experimental results show that the prototype can achieve high aperture efficiencies (>40%) within a wide bandwidth (34%). The measured peak aperture efficiency is up to 53% at 23 GHz. These results demonstrate that the proposed 2-bit transmitarray antenna enjoys the advantages of wide operating bandwidth, high aperture efficiency and comparatively low design complexity. With these characteristics, the proposed transmitarray antenna can be a promising candidate for vehicular communications that require reliable satellite links and 5G millimeter-wave connections simultaneously. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We recently proposed a direction-of-arrival (DOA) estimation method for the coexistence of uncorrelated and coherent signals, which is related to the uniform linear antenna arrays with mutual coupling (MC) in the presence of unknown nonuniform noise. This technique, however, relies on the assumption of mixed signals and is not suitable for scenarios with purely coherent signals. This paper extends the mixed signal scenario to the purely coherent signals one on one hand, and on the other hand, allows us to directly adopt the ESPPRIT algorithm to perform DOA estimation in MC environments. To be specific, with the help of the least squares (LS) criterion, the nonuniform noise is first eliminated, and the traditional middle subarray scheme can then be employed to be immune to the influence of MC. Unlike the former operation, following a different line of attack the latter can make full use of the whole array and provide a larger array antenna aperture. Furthermore, we derive a new strategy to directly determine the DOAs without taking MC into account and performing spectral search. This brings substantial benefits to the DOA estimation accuracy and computational cost. The superiority of the proposed approaches is verified by numerical examples. [ABSTRACT FROM AUTHOR]

State-of-the-art automotive radars have an angular resolution of 1°, which is insufficient for estimating the objects shape and boundaries at long distance. In this paper, we design a novel automotive radar with 1m aperture, which is an order of magnitude larger aperture than state-of-the-art automotive radars, and thus achieves super high angular resolution of 0.1°. The radar is designed to overcomes the major technical challenges of a wide aperture radar, which are: non-robust phase coherency over a wide aperture, spanning a wide aperture with sparse antenna elements, simultaneous non-interfering transmissions from a relatively large number of transmit antennas with unambiguous target speed estimation, and high complexity of near-field beamforming. We demonstrate the super high resolution performance of the radar in automotive scenarios, and show that it attains comparable results to a high resolution LIDAR at short range, and outperforms the LIDAR at long ranges. The wide aperture radar has the potential to enable autonomous driving at higher speed, and also to increase the operation of autonomous driving to more regions and climates. [ABSTRACT FROM AUTHOR]

In this study, we describe the specific features of the near-field distribution of a uniformly illuminated aperture. An analytical method based on physical optics in the time domain is used to calculate the field intensity. The primitive impulse response function makes it possible to calculate the near-field distribution of the antenna. The difference in the amplitudes of the fields during the observation point shift along the X and Y coordinate axes can reach up to 13% of their maximum relative values. This difference should be considered when calculating the antenna radiation patterns. At the end of this paper, we present the results of the comparison obtained using three methods: geometrical theory of diffraction (GTD), plane wave spectrum approach (PWS), and primitive impulse response function (IRF) method. In the near field of relatively small apertures (with respect to wavelength), the results of all three compared methods (GTD, PWS, and IRF) were very similar. The analytical IRF method, the results of which are given in this paper, is much more effective in terms of computer resources than the plane wave spectrum approach, and even more effective than the geometric theory of diffraction method.

Here, we propose a low-profile polarizing technique integrated in a parallel plate waveguide (PPW) configuration, compatible with fully metallic geodesic lens antennas. The geodesic shape of the antenna is chosen to resemble the operation of a Luneburg lens. The lens is fed with 11 waveguide ports with 10° separation producing 11 switchable beams in an angular range of $\pm \mathrm{50}^{\circ }$. Two metallic polarizing screens are loaded into the aperture of the antenna to rotate the electric field from a vertical linear polarization, which is the polarization of the transverse electromagnetic (TEM) mode supported in the lens, to a $+ \mathrm{45}^{\circ }$ linear polarization. Since the polarizing unit cells are integrated into the aperture of the antenna, the final design is compact. In addition, the size of the polarizing unit cells is about $0.55\lambda $ at the central frequency of operation making the antenna suitable to produce an array formed of stacked lenses. A prototype of the antenna in the $\text{K}_{\text {a}}$ -band was manufactured and tested, verifying the performance obtained in simulations. [ABSTRACT FROM AUTHOR]

This work presents a ${12}\,\,\times \,\,{12}\,\,\times \,\,{0.6}$ mm3 ball grid array (BGA) module made of low-cost organic substrates which integrates transmitter (Tx) and receiver (Rx) antennas for short-range 60 GHz WiGig communications. The Tx antenna is a single-element linearly polarized aperture-coupled patch (ACP) antenna achieving a worst −12 dB matching with a broadside realized gain above 5 dBi and a total efficiency higher than 50% in the 57–66 GHz band. The Rx antenna is a single-element single-fed circularly polarized ACP antenna. It exhibits a worst −14 dB matching level from ${57~}$ to 66 GHz and a worst −10 dB level from ${47~}$ to 66 GHz (33% relative bandwidth (BW) with respect to 60 GHz). The broadside realized gain is above 5 dBi from ${61~}$ to 67 GHz and the axial ratio stays below 3 dB for a 14% BW with respect to 60 GHz. Variability of the fabrication process is analyzed by means of extensive measurements of several modules. The effect of the integration of the module in the application PCB and the device casing is also studied for realistic use. The obtained results demonstrate suitability of this high-density interconnect BGA packaging technology for mass production of compact low-cost millimeter-wave (mmW) antenna module for WiGig communications. [ABSTRACT FROM AUTHOR]

This brief presents a high-efficiency shared-aperture multiple antenna system. Unlike general shared-aperture antennas, the proposed antenna system with the size of $0.384 {\times } 0.384 {\times } 0.171 {\mathrm {\lambda }} ^{3}$ makes high reuse the aperture in the two respective frequency bands, and the antenna structures of the two bands can each generate positive mutual enhancement for their radiating characteristics in the two bands. The flat Luneburg lens can realize beam steering capability for mm-wave antenna from 25.5 to 29.5 GHz with the gain of 19.3 dBi and improve the wide-angle scanning matching impedance for the Sub-6 GHz antenna from 3.2 to 3.45 GHz with the gain of 6.2 dBi. Meanwhile, as the radiating patch of the Sub-6 GHz antenna, the meta-surface can reduce the focal distance of the lens and maintain the high gain of the mm-wave antenna. Hence, a compact antenna system can achieve beam steering capabilities (up to 112°) in the Sub-6 GHz band and (up to 56°) mm-wave band with high gain, respectively. And the port isolation of the proposed antenna system between two frequency bands is generally better than 25 dB and even up to 40 dB at the Sub-6 GHz band. As reported in the simulated and measured results in a linear array, the antenna system shows good radiating performance with a dual-polarization state. Hence, the proposed multiple antenna system is a good candidate for 5G applications because of the high-efficiency, beam steering with high gain and full 5G band. [ABSTRACT FROM AUTHOR]

Based on the generalized frequency selective surface (FSS) theory, we prove that the dual-layer dual-polarization transmission FSS can achieve 360° phase coverage at a limited loss. As a verification, a dual-layer dual-polarization full-phase unit cell with vias is proposed, which can achieve a phase range of more than 360° under 2 dB transmission loss. In addition, we innovatively apply the proposed dual-layer full-phase FSS to the design of a continuous 2-D beam scanning antenna based on the Risley prism (RP). This scheme effectively reduces the number of dielectric substrate layers required by the phase shifting surface (PSS), reduces the rotating scanning inertia, and effectively improves the aperture efficiency. The measured results show that the maximum scanning range of the 2-D beam scanning antenna can reach ±46° in the elevation plane and 360° in the azimuth plane. When operating at the center operating frequency of 21 GHz, the maximum gain of the antenna is 35.75 dBi with an aperture efficiency of 44.1%. [ABSTRACT FROM AUTHOR]

In this article, a wideband shared-aperture phased array antenna is proposed for synthetic aperture radar (SAR) applications. A metal cavity-backed slot antenna and a slot antenna are used as the L- and X-band antenna elements, respectively. Notably, the X-band antenna elements are mounted on top of the L-band ones, and their interactions are successfully isolated by loading a layer of frequency selective surface (FSS). The FSS layer reflects the electromagnetic waves in X-band and allows transmission of the L-band electromagnetic waves, making the shared-aperture antenna work properly in L- and X-bands. Furthermore, a circular patch is designed to improve the bandwidth of the X-band antenna. Simulations indicate that the proposed antenna has impedance bandwidths of 46% in X-band (7.5–12 GHz) and 21% in L-band (1.7–2.1 GHz). Moreover, the X-band antenna can scan up to ±60° in the E-plane and ±30° in the H-plane with voltage standing wave ratio (VSWR) below 3. To verify the design method, a shared-aperture antenna prototype, which consists of $6\times6$ X-band elements and one L-band element, has been fabricated and measured. Finally, the measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

In this article, a cascaded metasurface (MS) with circular-polarization-selective properties is proposed, which can achieve high reflection for left-handed circular polarization (LCP) and high transmission for right-handed circular polarization (RCP). Such MS, constructed by cascading two kinds of MS sheets, can conduct decoupled geometric phase modulations for the LCP reflection channel and RCP transmission channel by respectively rotating the two elements in the two MS sheets. In order to show its practical applications, first, the proposed MS is applied to design a reconfigurable circularly polarized (CP) transmit-reflect-array antenna (TRA) that can be switched between a high-gain LCP transmitarray antenna and a high-gain LCP reflectarray antenna (RA) dependent on the polarization state of the feed antenna. The simulated results validate its function-switchable and high-gain characteristics. Second, a CP bidirectional antenna is designed utilizing the proposed MS and validated by a fabricated prototype with good agreement between the measured and simulated performances. The results indicate that the joint bandwidth (BW) for both forward and backward aperture efficiencies larger than 20% and axial ratios smaller than 3 dB is about 16% (9.4–11 GHz), across which the antenna realizes bidirectional high-gain and high-purity LCP radiations. [ABSTRACT FROM AUTHOR]

We present a C-band amplifying reconfigurable intelligent surface (ARIS) integrated with power amplifier (PA) to enhance the reflected electromagnetic (EM) signals. An aperture-coupled patch element with two orthogonal hourglass-shaped slots is elaborately constructed to ensure a broad operation bandwidth. A power combining and dividing network is also introduced to combine the 2 $\times2$ elements into a subarray to reduce the number of PAs and the system cost. The simulation results indicate that the achieved gain of ARIS is 7.7–12.2 dB from 5.0 to 6.0 GHz. A prototype of the proposed ARIS is designed, fabricated, and experimentally verified. The measured results agree well with the simulation. The proposed ARIS is promising for applications in future wireless communication systems for signal enhancement and coverage extension. [ABSTRACT FROM AUTHOR]

In this article, a wideband aperture-coupled stacked-patch (ACSP) antenna on a flexible material for wireless applications at the WR-08 band is presented. It is shown that conventional designs of ACSP fail to achieve a large bandwidth at this frequency range, and a novel design methodology is proposed. We first propose a broadband impedance matching between the input port and the slot aperture based on two-section wideband distributed network (TWBDN). We also propose a TWBDN matched stacked patch (TMSP) network based on constant VSWR circles to attain broadband matching between the slot aperture and patches in an ACSP. To facilitate the measurements, a novel low-loss transition from a ground-signal-ground (GSG) port to a feedline is proposed. The proposed structure suppresses surface waves induced in the WR-08 band by placing via arrays around the feedline, which largely reduces unwanted resonance modes, thereby leading to uniformly high radiation efficiency across the band. The measured results of the fabricated antenna closely follow the simulations, and a measured peak gain of 7.95 dBi and $S_{11}\leq -10$ dB across a wide frequency range from 90 to 128.5 GHz is achieved. [ABSTRACT FROM AUTHOR]

In the near-field meta-steering method, the near electric-field phase distribution is dynamically altered by rotating a pair of phase-gradient metasurfaces that are typically made out of dielectric lattices or metal patterns printed on bonded dielectric substrates. As a lightweight alternate, a new class of fully metallic metasurfaces (MMs) is proposed in this article. The lack of dielectrics not only substantially reduces the cost and weight but also increases its potential in space and high-power applications. More importantly, the new MMs are designed such that they can be made by cutting narrow slots in fully planar thin metal sheets, retaining structural rigidity while reducing the complexity, cost, and weight. The same MM works for any polarization. Each cell in the new MMs has close to ideal phase shift and transmission magnitude greater than −0.9 dB. A prototype was designed and fabricated to validate this MM-based beam-steering concept in the Ku-band. The maximum measured steering range in zenith is ±42°, with a full 360° steering in the azimuth. The measured 3 dB gain bandwidth is 700–800 MHz (5.6%–6.4%), and the measured gain variation (scan loss) when steering over the whole range is 2.2–4.5 dB. The weight density and thickness of each MM are 0.88 g/cm2 and $0.8\lambda _{0}$ , respectively. Including the feed, the total antenna height is $4.9\lambda _{0}$. [ABSTRACT FROM AUTHOR]

In this article, a concept of partial structure reuse is presented, and on this basis, a 3.5/28 GHz shared-aperture antenna supporting 2-D (endfire and broadside) steerable beams in the millimeter-wave (MMW) band is developed. The antenna consists of a 3.5 GHz planar inverted-F antenna (PIFA) and two 1 $\times $ 6 28 GHz substrate-integrated DRA (SIDRA) beam-steerable arrays, in which partial structures of the PIFA are reused by the two MMW arrays. To improve the performance of PIFA, two narrow slots and one lumped capacitor are introduced to reduce its H-plane cross-polarization and enhance the operating bandwidth, respectively. To verify the design, antenna prototypes were fabricated and measured. Measured results show that the antenna can cover a dual-band of 3.28–3.67 (11.2%) and 26–29.7 (13.2%) for the endfire and 25.9–29.7 GHz (13.8%) for the broadside. The peak gains of 4.8 and 10 (endfire) and 10.8 dBi (broadside) are obtained by the MW element and two 1 $\times $ 4 MMW arrays, respectively. Each of the MMW arrays can steer the beams from − 50° to + 50°, covering different parts of the space. The shared-aperture antenna has a compact size of 0.45 $\times $ 0.3 $\times \,\,0.03\lambda _{01}^{3}$ ($\lambda _{01}$ is the free-space wavelength at 3.5 GHz), making it suitable for terminal applications. [ABSTRACT FROM AUTHOR]

A novel W-band 2-D monopulse sparse array antenna with suppressed sidelobe levels is proposed in this article. The 2-D monopulse antenna is composed of a radiation sparse array, an irregular interconnected waveguide -based network, a power divider network, and a sum–difference network. The sparse array uses a box-horn as the radiation element and is optimized based on the genetic algorithm, which exhibits low sparsity and low sidelobe levels. The whole aperture of the antenna is divided into four subarrays. To feed all the radiating elements that are randomly distributed in the subarrays with the same amplitude and equal phase, an irregular interconnected waveguide -based network and a power divider network are designed. Finally, a sum–difference network is connected to the end of the four subarrays to obtain the sum and difference radiation performance results for the monopulse antenna. A 2-D monopulse sparse array antenna with 32 radiating elements is fabricated and measured. The measured $\vert \text {S}_{\mathbf {11}}\vert \le -10$ dB bandwidth of the antenna is over 6 GHz (from 90 to 96 GHz). At the center frequency, the maximal gain of the sum radiation pattern is approximately 24.0 dBi, with low sidelobe levels (both E-plane and H-plane) less than −19.0 dB. In addition, the null depth of the difference radiation pattern is less than −30.0 dB. [ABSTRACT FROM AUTHOR]

This article presents a Tx/Rx dual-band combined-aperture variable inclination continuous transverse stub (VICTS) antenna for low-earth-orbit (LEO) satellite-on-the-move (SOTM) applications. The beam directions for the Tx and Rx bands are kept consistent during beam scanning, so that the antenna allows a duplex link. The topology of the combined-aperture VICTS antenna is derived from the requirement for consistent beam directions. Nonuniform slow wave structures (SWSs) are used to achieve the required phase difference and phase-changing rate (PCR) between the radiation slots in the two bands, while maximizing the antenna efficiency. Predeflection technique is applied to the radiation slots to reduce the gain drop at a wide beam scanning angle. A prototype operating at K- and Ka-bands is designed, fabricated, and measured. Experimental results show that the antenna has a consistent beam direction during scanning in the frequency ranges of 19–21 GHz (Rx band) and 29–31 GHz (Tx band). The maximum beam directions in Tx and Rx bands exceeds ±47° at a relative rotation angle of 40°, and the gain drop during the beam scanning is reduced within 2.3 and 3.5 dB. [ABSTRACT FROM AUTHOR]

As reconfigurable intelligent surface (RIS) is expected to be implemented with a large aperture in terms of wavelengths, using a RIS to perform near-field rather than conventional far-field communications might gain some benefits. The electric fields in the near-field region from the near-field focusing and conventional far-field RISs are simulated and compared to assess and validate the benefits. Two metrics of benefit distance and near-field gain are defined to characterize the electric fields in the near-field region. The cumulative distribution function (CDF) related to the near-field gain is calculated to describe the benefits in the area of interest where the total scan patterns from the near-field focusing and conventional far-field RISs are plotted. For demonstration, the benefit distance, near-field gain, and CDFs are presented and calculated for near-field focusing RISs with assigned focal distances of 80 and 300 mm. It is concluded that the benefit distance is a critical factor affecting the CDF directly. The effects of the size of a RIS and phase quantization of elements on the benefit distance, near-field gain, and CDF are also discussed. Moreover, the maximum focal distance of a near-field focusing RIS with a certain size is derived and specified. Finally, the electric fields of three prototypes (e.g., conventional far-field RIS, near-field focusing RISs with assigned focal distances of 500 and 1500 mm) at 26 GHz are measured and compared, where the benefit distances and near-field gains are experimentally observed. [ABSTRACT FROM AUTHOR]

The irregularly located element array within the antenna aperture can be applied to obtain narrow main lobe width and low sidelobe levels with fewer elements as compared with the traditional (periodic) array configurations. In this article, a reconfigurable reflectarray antenna (RRA) combined with hyperuniform disordered distribution is presented. Based on the theoretical radiation pattern of reflectarray, it has been found that the proposed array with reduced elements holds a similar radiation pattern as that of a corresponding periodic array. Meanwhile, the reflectarray avoids the design of complicated feeding network for the disordered phased array antenna. In addition, for a reconfigurable reflectarray to achieve beam scanning, active devices are necessary. In such case, the design of RRA with fewer elements is of particular importance. A 1 bit RRA of 64 elements prototype has been designed, fabricated, and measured. The side length of each element is $0.625\lambda $. Experimental results agree well with the full-wave simulations, and scan beams within ± 50° range have been obtained with a peak gain of 17.4 dBi at 12.5 GHz. [ABSTRACT FROM AUTHOR]

A K-/Ka-band shared-aperture linear polarization (LP) phased array antenna and a circular polarizer are combined to realize circular polarization (CP) beam scanning. When the polarizer is close to the antenna array, its performance will become difficult to predict due to the influence of the antenna source. This will bring uncertainty to the cooperative work. We propose a codesign method of polarizer unit considering the factor of antenna array. This method can better design the polarizer working in the near field of antenna array. Next, to improve the CP scanning range, the polarizer is not composed of repeated units, but adopts a codesign partition scheme. We combine the polarizer unit specially designed for large-angle incidence and for normal incidence to a polarizer plane. The partition scheme is optimized with an algorithm according to the field distribution of antenna. This combination produces right-hand circular polarization (RHCP) at 19.7–20.2 GHz and left-hand circular polarization (LHCP) at 29.5–30 GHz, and the axial ratio (AR) of CP is less than 4 dB in the scanning range of $\pm 55^{\mathrm {\circ }}/\pm 60^{\mathrm {\circ }}$ at two operating bands. The proposed combination concept and the design results have been validated by the experimental results. [ABSTRACT FROM AUTHOR]

Based on the newly suggested wideband circularly polarized (CP) aperture-coupled magneto-electric dipole (MED), a millimeter-wave (mm-wave) frequency-scanned array (FSA) is proposed in this article. The MED is printed on two substrate layers. The electric dipole is two metal patches with perturbation structure, while the magnetic dipole is two rows of metal vias passing through the top substrate layer. The electric and magnetic dipoles, fed by a coupling slot, excite CP wave. By loading an arc-shaped vias row (AVR) at both ends of the magnetic dipole, the CP bandwidth with axial ratio (AR) less than 3 dB is extended to 40.9%. A new compact wideband transition from the rectangular waveguide (RWG) to the substrate integrated waveguide (SIW) is suggested as the feed structure for the CP FSA. A slow wave structure is etched on the ground of SIW to widen the beam scanning range. A 16-element array is designed and measured. The measured results show that the beam scanning range is 56° over 23–33 GHz band with a peak gain of 19.5 dBi. The CP mm-wave FSA has the advantages of wide scanning angle, low profile, and easy fabrication. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate that a circular advanced short backfire antenna (A-SBFA) can be optimized for high single- or dual-band aperture efficiency over a range of different aperture sizes. Optimization methods developed previously to utilize anisotropic, dispersive metasurfaces on the cavity walls of the hexagonal A-SBFA are modified and applied to achieve 100% aperture efficiency at two frequency bands for circular aperture diameters spanning a remarkably large range from $1.0\lambda _{0}$ up to $2.13\lambda _{0}$. Furthermore, a single-frequency optimization was able to achieve a design with 100% aperture efficiency for an A-SBFA with a diameter of $2.6\lambda _{0}$ , the highest known achievable efficiency for an antenna of its aperture size, and overall height. Finally, simulations revealed the first compact hard horn or open-ended waveguide design with close to 100% aperture efficiency below $1.6\lambda _{0}$. [ABSTRACT FROM AUTHOR]

We introduce and discuss a new approach to the phase retrieval (PR) of fields radiated by continuous aperture sources having circular support, which is of interest in many applications, including the detection of shape deformations on reflector antennas. The approach is based on a decomposition of the actual 2-D problem into a number of 1-D PR problems along diameters and concentric rings of the visible part of the spectrum. In particular, the 1-D problems are effectively solved by using the spectral factorization method, while discrimination arguments at the crossing points allow completing the retrieval of the 2-D complex field. The proposed procedure just requires a single set of far-field amplitudes (but for an additional bit of information) and takes advantage from up-to-now unexplored field properties. The developed technique is assessed in the case of reflector aperture fields. [ABSTRACT FROM AUTHOR]

A Ku-/Ka-band shared-aperture 2-D phased array antenna is proposed in this article. The antenna consists of an 8 × 8 Ku-band vertical-polarized dipole antenna array fed by a microstrip line to strip line transition and an 8 × 8 Ka-band horizontal-polarized waveguide antenna array fed by a microstrip line to substrate integrated waveguide (SIW) to fin line transition, which can be used to connect with T/R modules. For a dual-band radar system, the main challenge is to realize the shared-aperture array antenna having the wideband wide angle in the lower band and well-performed in the higher band. For example, the relative bandwidths of 25% in the Ku-band and 11.4% in the Ka-band are necessary for this work. The bandwidth of both bands is wider than that of existing works. To satisfy the wideband and wide beam coverage in two dimensions simultaneously, wideband radiating elements for both two bands are used. In this case, due to the wideband Ku-band radiator, the blind area in the Ka-band appears within the scanning process because of the parasitic mode, which should be eliminated by properly adjusting the Ku-band radiator. After that, the scanning angles of ± 60° at 14 GHz, ± 50° at 16 GHz, and ± 35° at 18 GHz, and ± 40° at 33 GHz, ± 40° at 35 GHz, and ± 35° at 37 GHz can be achieved in both E- and H-planes, respectively. Each Ku-band linear array is tightly inserted into its two adjacent Ka-band linear arrays along the wide side of the Ka-band element. Thanks to the extremely thin Ku-band endfire dipole antenna, the radiating aperture size of the Ka-band array keeps unchanged after adding the Ku-band radiators. The proposed antenna concept has been validated well by the experimental results. [ABSTRACT FROM AUTHOR]

The dc power collected by radio frequency energy harvesting (RFEH) absorbing surfaces is limited by their physical aperture. Here, a compact, conformable, and ultrathin sub-1 GHz large-area RFEH surface is proposed based on electrically small ($ka=0.58$) “wire-type” rectenna elements, with an effective area exceeding its physical aperture size. Using optimized large-signal complex source tuning, the rectifiers achieve up to 36% measured power conversion efficiency (PCE) at =20 dBm. The proposed 15 cm-diameter six-element array generates a 27.5 $\mu \text{W}$ at 1 V output from a $0.17~\mu \text{W}$ /cm2 incident power density across a 40 $\text{k}\Omega $ load. Owing to its series connection, the voltage output is boosted, and the load resistance dependence is suppressed enabling over 60% of the maximum RF-to-dc PCE to be preserved for loads between 7 and 100 $\text{k}\Omega $ , with an area-normalized figure-of-merit nearly 100% higher than previous arrays. The proposed array is integrated with a commercial DC-DC converter and demonstrated powering a Bluetooth low energy (BLE) wireless sensor node (WSN) from an unprecedented incident power density of 0.25 $\mu \text{W}$ /cm2. A practical demonstration using a commercial 3 W, 915 MHz Powercast source is presented, showing an 11 m operation range with a 1 V output and illustrating the impact of polarization mismatch on the proposed array. [ABSTRACT FROM AUTHOR]

A wide variety of desirable antenna beam patterns can be synthesized by optimal excitation and phasing of the HE11 and HE12 modes in scalar corrugated feedhorns. However, the bandwidth of such two-mode horns is often limited by modal dispersion. In this paper we introduce a class of low dispersion, two-mode feedhorns that can operate, in some cases, over operating bandwidths of 40-50%. We provide example designs that include horns with high coupling efficiency to: 1) a pure HE11 mode for single-mode excitation of corrugated pipe transmission lines; 2) a LG00 and LG02 combination for radiometry, with narrow beams; 3) a pure Laguerre Gaussian LG00 mode for quasi-optical instrumentation with constant phase centers; 4) a constant gain antenna for uniform illumination with frequency; 5) Airy patterns or “top hat” patterns for radar or communications applications, designed to maximize aperture efficiencies when used with larger reflect or lens antennas. More generally, we show methods to generate and phase multiple ${\text{HE}}_{1n}$ modes, to synthesize symmetric output beams at any desired frequency or gain.

A novel miniaturized, aperture-shared, vertically polarized (VP), zeroth-order resonance (ZOR)-based, metasurface antenna with pattern reconfigurability is proposed for sub-6 GHz fifth-generation (5G) application in this article. By exploring an aperture-shared ZOR metasurface with only four p-i-n diodes, the proposed pattern reconfigurable metasurface radiator can be operated at nine radiation states (one omnidirectional beam and eight scanning beams with 45° step). This novel reconfigurable ZOR metasurface is analyzed by equivalent circuit, array theory, and field distribution. To validate the proposed working principles and design guidelines, this VP metasurface-based pattern reconfigurable antenna with a low profile of $0.05\lambda _{0}$ is fabricated and measured. It exhibits an 11.5% overlapped −10 dB impedance bandwidth (3.40–3.8 GHz, well covering B42/B43 LTE bands) and a 4.5 dBi peak gain in different radiation states. With the advantages of a miniaturized size (low profile), broadband, flexible pattern switching capacity, good radiation performance, and simple design, it is well poised for space-limited sub-6 GHz microcell applications. [ABSTRACT FROM AUTHOR]

In this article, a single-sheet metasurface (MS) for independently manipulating the transmissive phase and amplitude of linearly polarized electromagnetic (EM) wave is proposed. The amplitude modulation is achieved via imposing a rotation angle to flexibly control the ratio of polarization conversion, while the phase modulation is realized by tuning the physical parameters of the unit cell to change its resonance. By integrating the proposed single-sheet MS, a low-profile metalens antenna operating around 12.2 GHz is designed, fabricated, and experimentally validated. In particular, spatially varying amplitude on the MS aperture is designed to meet the Taylor distribution, thus reducing the sidelobe level (SLL) of the metalens antenna. In addition, special MS elements rotation strategy is performed to maintain good polarization isolation-level (PIL) performance. The measured results show that the proposed metalens antenna achieves the peak gain of 25.3 dBi at 12.6 GHz with 3 dB gain bandwidth of 16.4% (11.2–13.2 GHz). Within the 3 dB gain bandwidth, this metalens antenna achieves SLL lower than −20.5 dB with an average value of −23 dB and PIL lower than −22.2 dB with an average value of −26.5 dB. Compared with metalens antenna with phase-only modulations, the proposed metalens antenna realizes a 5.7 dB average SLL suppression. The proposed metalens antenna is a promising candidate in point-to-point communications for wireless and satellite system applications. [ABSTRACT FROM AUTHOR]

In this article, the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an $LC$ series resonator modeling the feed plus two capacitively coupled $LC$ parallel resonators accounting for the radiating patches. Then, a deembedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modeling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments. [ABSTRACT FROM AUTHOR]

The optimal design of aperiodic/irregular clustered phased arrays (PAs) for base stations (BSs) in multi-user (UE) multiple-input–multiple-output (MU-MIMO) communication systems is addressed. This article proposes an ad hoc synthesis method aimed at maximizing the UEs traffic capacity within the cell served by the BS while guaranteeing a sufficient level of the signal at the terminals. Toward this end, the search of the optimal aperiodic clustering is carried out through a customized tiling technique able to consider both single and multiple tile shapes and assure the complete coverage of the antenna aperture for the maximization of the directivity. Representative results, from a wide set of numerical examples concerned with realistic antenna models and benchmark Third Generation Partnership Project (3GPP) scenarios, are reported to assess the advantages of the irregular array architectures in comparison with regular/periodic layouts proposed by the standard development organizations as well. [ABSTRACT FROM AUTHOR]

This article presents a new type of beam-tilted circularly polarized (CP) radial line slot array (RLSA) antennas. When the conventional beam tilting method is applied to CP-RLSA antennas, the aperture efficiency of the antenna degrades significantly due to very sparse slots in some parts of the antenna. A new method is presented to prevent this, and hence a much higher gain and aperture efficiency are achieved from the same antenna area. The key to the new method is an aggressively biased truncation of the slot layout that leaves out sparse slots. Consequently, the feed point moves closer to an edge of the TEM waveguide. A reflecting wall is introduced to prevent leakage from this edge. It is shown that the gain of RLSAs with beams tilted to 25° and 45° (measured from normal direction) can be increased by 5.5 dB (from 20.5 to 26 dBic) using the new method as opposed to the conventional method. The new concept and predicted results are validated using a prototype antenna with the beam-tilted to an angle of 25°. The aperture diameter and overall thickness of the prototype are $12\lambda _{0}$ and $0.4\lambda _{0}$ , respectively, where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 18 GHz. The measured results confirmed a higher gain of 26.2 dBic, an aperture efficiency of 30%, the overall efficiency of 93.2%, and sidelobe levels (SLLs) less than −25 dB at 18 GHz. The measured 10 dB return loss bandwidth of the antenna is greater than 63.7%, 3 dB axial-ratio bandwidth is 13.3%, and 3 dB gain bandwidth is 6.7%. [ABSTRACT FROM AUTHOR]

This article introduces an amplitude and phase independently adjustable transmitarray aperture with a thin profile and low cost to fabrication characteristics, and a transmitarray antenna (TA) featuring the high gain and low sidelobe level (SLL) is realized based on it. The TA is made up of a standard feed horn and a transmitarray aperture, each of which comprises a three-layer metasurface that is well-designed to tune the transmitted phase and amplitude on its own. As a result, the transmitarray aperture can cover the 360° phase range required for phase compensation while also realizing the amplitude distribution calculated by the Taylor design, contributing to the low SLLs. The advantage of independently controlling the amplitude and phase not only enables the proposed TA to be easy to realize and less cost on optimization but also improves the performance of high gain and low SLLs with a low profile and easy fabrication. Theoretical analyses and simulations are carried out, and a prototype is fabricated and measured. At 10 GHz, the measured peak gain is 21.16 dBi, with SLLs of −31.21 and −29.93 dB in the H- and E-planes, respectively. As a result, the tight agreements between measurement and simulation validate the design concept. [ABSTRACT FROM AUTHOR]

A millimeter-wave (mm-wave) system architecture with enhanced-gain antenna solution is proposed for fifth-generation (5G) wireless communications. To enhance the antenna gain, the surface wave currents are converted to constructive far-field radiations through a novel two-stage metallic and dielectric rings. By applying low-profile dielectric ring, the electric near-field distributions of the grounded quarter-wavelength metallic ring are modified to create radiation apertures with appropriate polarization and orientation. The mutual coupling between transmit/receive antennas and cross polarizations is reduced by 7 and 5 dB, respectively, and the gain is enhanced over 4 dB. Low-loss mm-wave transitions are implemented in a standard FR-4 printed circuit board and in an interposer substrate to integrate the active antenna with the rest of the wireless system on a compact universal serial bus (USB)-interface platform. To evaluate the interposer package and define the output power of the embedded 60-GHz RF IC, an evaluation module with a standard WR-15 waveguide interface is designed and implemented. A prototype of the architecture, which is entirely realized using low-cost organic substrates, is presented and evaluated by experiments. Excellent correlations are achieved between simulations and measurements, demonstrating more than 25 dBm of equivalent isotropically radiated power (EIRP) over the unlicensed 60-GHz frequency band. [ABSTRACT FROM AUTHOR]

A new approach is proposed to develop aperture-shared dual-band antennas using partially reflecting surfaces (PRSs). A fully aperture-shared dual-band antenna consisting of a low-band antenna (LBA) and a high-band antenna (HBA) right below the LBA is first investigated. The aperture sharing has little influence on the LBA but causes a severe shielding effect on the HBA. To alleviate the shielding effect, a low-pass PRS is inserted between the LBA and HBA, forming an air-filled quasi-Fabry–Perot cavity, which can make compensation for the radiation from the HBA but with little influence on the LBA. The second PRS is introduced above the LBA to enhance the bandwidth (BW) for HBA. It is shown that the fully aperture-shared dual-band antenna achieves an impedance BW ($\vert \text{S}11\vert < -15$ dB) of ~43.7% (0.68–1.07 GHz) for the LBA and ~45% (1.7–2.7 GHz) for the HBA with an average gain of ~8 dBi and stable radiation patterns. Based on the PRSs, an aperture-shared dual-band antenna subarray is finally developed for base-station applications, which covers the frequency bands of 0.68–0.96 and 1.7–2.7 GHz for 2G/3G/4G mobile communications. [ABSTRACT FROM AUTHOR]

A phased array loaded with a reactive impedance surface (RIS) is proposed for wideband wide-scanning performance. The mushroom-like RIS structure, etched on the same printed circuit board (PCB) of the antenna, is introduced as a superstrate over the antenna aperture. The reactance of the RIS structure compensates for the scan impedance variation of the antenna during the beam scanning, explained by the equivalent transmission-line model. A superior scanning performance in all azimuth planes is achieved, and the scan blindness in the H-plane is alleviated, especially. The total compact design is capable of operating over a 2.3:1 (6 –14 GHz) bandwidth in broadside and over a 1.8:1 bandwidth in ±60° E-plane, ±70° D-plane, and ±65° H-plane scanning. The array is implemented in a triangular lattice, and edge elements in the E-plane are connected to metal walls for edge effect elimination. A 45-element ($5\times 9$) array prototype is fabricated and measured. Active reflection coefficients are calculated, and scanning patterns are synthesized. [ABSTRACT FROM AUTHOR]

The modular design of planar phased arrays (PAs) arranged on orthogonal polygon-shaped apertures is addressed and a new method is proposed to synthesize domino-tiled arrays fitting multiple, generally conflicting, requirements. Starting from an analytic procedure to check the domino-tileability of the aperture, two multi-objective optimization techniques are derived to efficiently and effectively deal with small and medium/large arrays depending on the values of the bounds for the cardinality of the solution space of the admissible clustered solutions. A set of representative numerical examples is reported to assess the effectiveness of the proposed synthesis approach also through full-wave simulations when considering nonideal models for the radiating elements of the array. [ABSTRACT FROM AUTHOR]

A collocated phased-subarray multiple-input and multiple-output (MIMO) radar system that reduces the number of MIMO channels to implement a large antenna array is proposed. Both the transmitter (TX) and receiver (RX) arrays are divided into phased subarrays, which consist of several RF beamforming antenna elements. Each phased subarray is exploited as an MIMO channel. To estimate the angular information of targets, a hybrid beamforming technique that incorporates RF beamforming of the phased subarrays and digital beamforming of the MIMO virtual array is used. Antenna configurations of the phased-subarray MIMO radar and the corresponding virtual array are also presented. A space between the TX phased subarrays larger than one TX subarray aperture is introduced to facilitate the larger antenna aperture. Because this involves unwanted overall grating lobes, a grating lobe cancellation method is proposed using sum and difference RF subarray beams. This provides a higher angular resolution with the same number of antenna elements. The proposed phased-subarray MIMO radar concept with the corresponding grating lobe cancellation method is demonstrated by implementing a 60-GHz 16-element phased-subarray 2 ${\times }$ 2 MIMO frequency-modulated continuous-wave (FMCW) radar system. [ABSTRACT FROM AUTHOR]

Soil Moisture and Ocean Salinity mapping by Earth observation satellites has contributed significantly toward a better understanding of the Earth system, such as its hydrosphere or climate. Nevertheless, an increased spatial resolution below 10 km with a radiometric resolution in the range of 2 K–3 K of radiometric data could yield a more complete picture of global hydrological processes and climate change. Operational radiometers, such as SMOS, have already approached prohibitive sizes for spacecraft due to the required large antenna apertures. Therefore, radiometer concepts based on a large number of satellites flying in close proximity (swarms) have been proposed as a possible solution. This article investigates the orbit mechanics of placing a satellite swarm-based motion induced synthetic aperture radiometer (MISAR) in low Earth orbit for Earth observation applications. The aperture synthesis antenna array is formed by a large number of individual antennas on autonomously controlled nanosatellites (deputies) and a correlator antenna in the Y-configuration carried by a chief satellite. The proposed design methodology is based on the optimization of satellite positions within a plane and the subsequent translation of coordinates into initial conditions for general circular orbits (GCOs). This enables a more computationally efficient orbit optimization and ensures the time invariance of the antenna array response. Based on this methodology, simulations have been performed with swarms consisting of up to 96 satellites. Simulations show that the spatial resolution of an aperture synthesis radiometer can be increased to less than 10 km for applications where the requirements on radiometric sensitivity are more relaxed ($\Delta T\sim 3$ K). [ABSTRACT FROM AUTHOR]

This work presents a design of an aperture-coupled complementary antenna for realizing circularly polarized (CP) broadside radiation at millimeter-wave (mm-wave) frequencies. The proposed antenna constructively combines a patch dipole (electric dipole radiation) and a folded loop antenna (magnetic dipole radiation), which are differentially excited by a longitudinal slot etched on the top layer of the substrate integrated waveguide (SIW). The combination of the proposed patch dipole and the folded loop antenna results in a paralleled electric dipole and magnetic dipole which can generate two orthogonal electric field components and 90° phase difference in the far-field radiation when they are in-phase excited. The proposed antenna achieves a wide impedance bandwidth of 46% from 48.47 to 77.46 GHz and a wide 3 dB axial ratio bandwidth (ARBW) of 47.3% from 51.64 to 83.61 GHz with an overlapped bandwidth of 40%. To further enhance the antenna gain, sequential rotation technique is adopted to construct a $2 \times 2$ subarray, which is further employed in a $4 \times 4$ subarray. The $4 \times 4$ subarray is then used to construct an $8 \times 8$ antenna array, which achieves a wide impedance bandwidth of 33.8% from 56.11 to 78.95 GHz and a wide 3 dB ARBW of 38.8% from 53.57 to 79.32 GHz, with a maximum antenna gain of around 25.2 dBic. The proposed antenna element and array design would be a competitive candidate for future wireless applications operating at mm-wave spectrum. [ABSTRACT FROM AUTHOR]

In this article, a triple-band shared-aperture dual-polarized antenna array is proposed for fifth generation (5G) base station applications. The shared-aperture antenna array consists of an antenna operating in the low-band (LB) 0.69–0.96 GHz, a $2\times $ 2 antenna array operating in the middle-band (MB) 1.8–2.7 GHz, and a $4\times $ 4 antenna array operating in the high-band (HB) 3.3–3.8 GHz. A wideband bandstop frequency selective surface (FSS) is introduced to eliminate the influence of the LB antenna on the MB/HB antenna array. The MB antenna is co-designed with the wideband bandpass FSS, such that it does not affect the radiation performance of the HB antenna array. Therefore, the LB antenna, MB antenna array, and HB antenna array are successfully integrated within a compact volume of $0.69\lambda _{L} \times 0.69\lambda _{L} \times 0.177\lambda _{L}$ ($\lambda _{L}$ is the free-space wavelength at 0.69 GHz). Measured results demonstrate that the proposed low-profile shared-aperture antenna array offers stable radiation patterns and an average gain of 6.5, 7.6, and 8.2 dBi in the LB, MB, and HB, respectively. Owing to the wide bandwidth, low-profile height, shared-aperture, and compact size, the proposed antenna array is promising for 5G massive MIMO applications. [ABSTRACT FROM AUTHOR]

This article presents the design, fabrication, and testing of a modulated metasurface (MTS) antenna for monopulse radar tracking at Ka-band. The antenna consists of a circular, thin grounded dielectric layer printed by a texture of metallic patches modulated in shape and size. The patch layer can be modeled as a spatially variable capacitive impedance sheet, which together with the grounded slab contribution provides an overall, modulated, inductive boundary condition (BC). The antenna aperture is divided into four identical angular quadrants each of them radiating independent broadside beams when excited by an individual monopole launcher. Each of the four launchers excites a TM cylindrical surface wave (SW), which is progressively converted into a leaky-wave (LW) by the MTS. The four subapertures are virtually separated by properly designing the MTS modulation. To this end, the LW attenuation constant is calibrated for dumping sufficiently each individual SW, thus preventing the interaction between the adjacent regions. Therefore, the printed structure is not delimited by any physical separation, but only by a continuous change of the equivalent BCs. The monopulse-type linearly polarized $\Sigma $ , $\Delta \Delta $ , $\Delta _{\mathrm{ E}}$ , $\Delta _{\mathrm{ H}}$ beams are obtained by combining the source excitation with a simple phasing scheme. Notably, this solution does not affect the overall lightness, low profile, feed simplicity, and low fabrication cost of the structure, which constitutes an inherent advantage with respect to more traditional waveguide-based solutions. [ABSTRACT FROM AUTHOR]

The shared aperture antenna is regarded as one of the promising approaches to support new frequencies with very efficient space utilization. To the best of the authors’ knowledge, there are few shared aperture antennas that include both the sub-6 GHz antenna and the millimeter-wave (mm-wave) beam-steering array for broadside applications. In this article, a broadside sharing aperture technique is developed so that a 2 $\times4\,\,26$ GHz beam-steering substrate-integrated DRA (SIDRA) array can be integrated into a 3.5 GHz bandwidth enhanced perforated patch antenna in a coplanar and aperture-shared way. The proposed solution benefits from several aspects. First, the 3.5 GHz antenna features a compact size as this part is built on the substrate (where the mm-wave SIDRA is constructed) with a high permittivity. Second, the mm-wave SIDRA is a 3-D-type device, and in the case of coplanar integration, its height can be freely adapted to the thickness of 3.5 GHz antenna without concerning the impact from surface waves as many 2-D-type antennas have to do. Third, the antenna can be implemented with the multi-layer printed circuit board (PCB) process, yielding a high integrity level. The dual-frequency antenna was designed, fabricated, and measured. The performances of the antenna are reported with reasonable agreement between the measured and simulated results observed. [ABSTRACT FROM AUTHOR]

This article presents a frequency selective surface (FSS)-based dual-band dual-polarized antenna with compact size and high gain. The proposed dual-band antenna consists of a low-band (LB) and high-band (HB) antenna elements. The HB element is coaxially located under the radiator of the LB element, minimizing the overall size. The proposed LB element consists of a two-layer-FSS-based radiator (FSS-radiator) and two pairs of differential feeding probes. Besides, the passband of the proposed FSS-radiator is designed to cover the operating band of the HB element. As a result, the radiation of the HB element can transmit through the FSS-radiator of the LB element. Without reducing HB element gain, instead, the average HB element gain can be improved more than 1 dB by the feeding probes of the LB element. For demonstration, a prototype of the dual-band antenna operating in the LB of 2.3–2.7 GHz and the HB of 3.3–3.8 GHz is fabricated and measured. The dual-band prototype features high gain (~9.1 dBi in the LB and ~8.6 dBi in the HB) in a compact radiation aperture of $0.32\lambda _{lc} \times 0.32\lambda _{lc}$ or $0.45\lambda _{hc} \times 0.45\lambda _{hc}$ (where $\lambda _{lc}$ and $\lambda _{hc}$ , respectively, denote the guided wavelengths at the central operating frequencies in LB and HB). Moreover, easy fabrication and low cost are achieved. These merits make the proposed antenna suitable for multiband aperture-shared array. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MTAI) has been widely used in biomedical science, and has the potential as an auxiliary measure for clinical diagnosis and treatment. Recently, there are increasing interests in using ultrashort microwave-pumped thermoacoustic imaging techniques to obtain high-efficiency, high-resolution images. However, the traditional imaging system can only provide uniform radiation in a relatively small area, which limits their large field of view in clinical applications (such as whole-breast imaging, brain imaging). To address this problem, we propose an ultrashort pulse microwave thermoacoustic imaging device with a large size aperture antenna. The system can provide a microwave radiation area of 40 cm × 27 cm and a uniform imaging view of 14 cm × 14 cm. With 7 cm imaging depth and a 290 μm resolution. The practical feasibility of the system for breast tumor screening is tested in phantoms with different shapes and in an ex vivo human breast tumor which is embedded in the excised breast of an ewe (π × 5 cm × 5 cm). The tumor can be identified with a contrast of about 1:2. The results demonstrate that the dedicated MTAI system with the uniform large field of view, high imaging resolution, and large imaging depth have the potential for clinical routine breast screening. [ABSTRACT FROM AUTHOR]

We introduce a novel formulation for flat radial GRadient INdex (GRIN) lenses allowing for the optimal lens design through closed-form expressions. The validity of the proposed formulation covers a very large range of GRIN lens design parameters (focal distance, lens thickness, and maximum refractive index). The formulation is based on the derivation of a new form of nonlinear integral equation representing the equalization of all the optical ray-path lengths, denoted as regularized ray congruence (RRC) equation, and on its closed-form solution. An analytical form of aperture efficiency is given for standard feed patterns. The application of the formulas presented here allows for an instantaneous design for medium/high gain antennas with controllable total aperture efficiency till 80%. The accuracy of the formulation is tested by a full-wave analysis and compared with other formulations available in the literature. We found that the new formulation proposed here significantly reduces the phase error in a wide range of the lens parameters, thus allowing for a more efficient, accurate, and flexible design for GRIN lenses. As a proof of concept, a thin GRIN lens antenna for operation in E-band (60–90 GHz) is designed, demonstrating high aperture efficiency (63%) across a wide frequency range. [ABSTRACT FROM AUTHOR]

In this article, a low-profile compact array antenna using polarization-agile and frequency-tailored capabilities with digital-controllable radiation beams is presented. The antenna element consists of a square patch loaded by four capacitors and four switchable feeding ports which are controlled by a field-programmable gate array (FPGA). The frequency of the resulting structure can be altered from 1.35 to 2.19 GHz based on a compact size by choosing different capacitance values from 0.31 to 3.14 pF. By designing the coding patterns of the digital radiating elements, various radiation beams with three different linear polarization (+45°-LP, −45°-LP, and V-LP) can be achieved and arbitrarily controlled based on one antenna aperture. The simulation and experimental results demonstrate an acceptable agreement, which proves the polarization-agile and beam-controllable characteristic of the designed array antennas at three different frequency bands corresponding to 0.3, 1.0, and 3.0 pF. The multifaceted reconfiguration capability enables it to meet the needs of signal quality stability in many future communication systems. [ABSTRACT FROM AUTHOR]

A millimeter-wave high-gain dual-polarized antenna array with an enhanced bandwidth is presented. An innovative air-filled differential feeding cavity loaded with a short-ended cross-shaped waveguide is investigated to serve as the feed network and the mode splitter simultaneously of the $2\,\,\times2$ dual-polarized subarrays. Wideband characteristics and a compact planar size that are desirable for the wideband array design are achieved. Moreover, a wideband dual-polarized waveguide-fed magnetoelectric (ME) dipole antenna with a lightweight self-support geometry and wideband H-plane parallel feed networks with modified dual-layered configurations are proposed, which are convenient to connect with the differential feeding cavity directly. With the use of a commercial metallic 3-D printing facility, the proposed radiating elements, feeding cavities, and feed networks can be combined successfully in a whole piece with a lightweight geometry. The printed $8 \times 8$ array prototype operating in the Ka-band confirms a wide bandwidth of about 30%, a gain of up to 28.5 dBi, and stable unidirectional radiation patterns for the two polarizations. Benefitted from the advantages of the promising wideband dual-polarized radiations and convenience of fabrication, the proposed antenna array would be attractive for millimeter-wave polarization diversity applications. [ABSTRACT FROM AUTHOR]

In this article, a new H-plane horn antenna is designed using gap waveguide (GW) technology. This antenna consists of a semicircular groove GW (GGW) partially filled by a dielectric to provide uniform field distribution across the antenna aperture in a very compact range. In the proposed structure, the antenna aperture is loaded by an elliptical dielectric which collimates the antenna beam in E-plane resulting in gain enhancement. The designed antenna shows proper radiation performance in both E- and H-planes with low sidelobe levels (SLLs). A sample antenna is designed and simulated for Ku band and a prototype is fabricated. For the designed antenna, the impedance bandwidth ($S_{11} < -10$ dB) of 49% covering the whole Ku-band is obtained. Likewise, the obtained SSL and gain are −10 dB and 14–17 dBi, respectively, over the operating bandwidth. In comparison with state-of-the-art designs, the proposed antenna introduces higher gain with lower size. [ABSTRACT FROM AUTHOR]

This article presents an aperture-shared dual-band large frequency-ratio high gain antenna for sub-6 GHz and millimeter-wave (mm-wave) bands applications. Initially, the partially reflective surface (PRS) of the Fabry–Pérot cavity (FPC) antenna operating at the sub-6 GHz band is realized by using single-layered periodic grid patches while the opaque region of the mm-wave bandwaveband Fresnel zone plate (FZP) lens antenna is implemented by using periodic double-screen dipoles. Then, the PRS and the FZP lens are hybridized together and upgraded into a kind of composite metasurface, which simultaneously functions as the PRS of the sub-6 GHz FPC antenna and the mm-wave bandwaveband FZP lens with little dual-band mutual interference. Thus, the FPC antenna and the FZP lens can share the same aperture with high aperture reuse efficiency. Because the principles are based on the FPC resonance and the collimating FZP lens, high gains are achieved at both bands without a feeding network. Meanwhile, a dual-band large frequency-ratio antenna is designed as the feed. A prototype working at 3 and 28 GHz bands is designed, fabricated, and measured to verify the idea. [ABSTRACT FROM AUTHOR]