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This study provides the design and demonstration of a Ku/K band horn‐fed linear polarization (LP) to circular polarization (CP) converter using a reflectarray antenna based on the holographic technique and the generalized law of total reflection without any iterative algorithms. The proposed hologram performs wide‐range frequency beam scanning with minimum gain losses and cross‐polarization levels. It comprises 2,500 diagonal slotted octagonal subwavelength metasurfaces with a periodicity of 0.266λ0 = 4 mm at 20 GHz as the center frequency. Two equations are defined to compute Y11 of the proposed unit cell regarding its dimensions for TE(0,0) and TM(0,0) Floquet modes. They significantly simplify the coding procedure and reduce the computational time for synthesizing the hologram. The antenna is simulated using the CST software from 14 to 25 GHz. As a confirmation, a prototype is manufactured and measured at 16, 18, 20, 22, and 24 GHz to verify its performance. The simulated and measured results are well‐matched. The presented hologram achieves 40% 1.8‐dB axial ratio (AR) bandwidth (16–25 GHz), 40% 3.3‐dB gain bandwidth (16–24 GHz), and above 30% 2‐dB gain bandwidth (16–22 GHz). Moreover, the antenna can perform beam scanning from 42° to 24° by changing the frequency from 16 to 24 GHz with peak gain values greater than 20.33 dBi. The LHCP pencil beams are at least 24° off‐broadside, so the proposed hologram avoids the feed blockage. These achievements make the hologram one of the best candidates for satellite communications, radar applications, short‐range communication, and point‐to‐point communication. Key Points: The antenna is designed based on the holographic technique and the law of total reflection for Ku and K band applicationsThe antenna frequency scans its main LHCP beam in a wide range with a high gain and low lossThe antenna performs LP to LHCP conversions with a wide axial ratio bandwidth and low cross‐polarization levels [ABSTRACT FROM AUTHOR]

Abstract This paper presents a feasibility study of a singlylayered dual-band reflectarray for space applications. The data links should operate simultaneously at K-band downlink frequency band 17.7-20.2 GHz with left-hand circular polarization (LHCP) and at Ka-band uplink frequency band 27-30 GHz with right-hand circular polarization (RHCP). The main aim is to present how a reflectarray can be designed so as to allow reconfigurability of its radiation pattern, especially in terms of beam steering to two different directions. The design is automated by means of a computational tool developed in MATLAB environment interfaced with the electromagnetic simulator CST Studio Suite by means of Visual Basic scripts. Simulation results are presented to demonstrate the efficiency of the proposed computational tool and reconfiguration strategy.

The feed for reflectarrays and transmitarrays is crucial for determining the overall antenna aperture efficiency, gain, and power handling. In the past, several methods, such as altering the horn shape to achieve higher modes, have been employed to modify the feed radiation pattern to improve these key parameters. However, another approach is to use gradient index (GRIN) lenses, which offer unprecedented control over the radiation pattern and can be used to shrink the overall antenna. In this paper, we demonstrate highly effective approaches for optimizing GRIN lenses to achieve different design objectives including high gain radiation with a compact feed as well as improved aperture efficiency and power handling. Additive manufacturing is employed to fabricate the lenses, and measured results agree well with simulations.

Reflectarrays (RAs) exhibit important advantages over conventional antenna arrays, especially in terms of realizing pencil-beam patterns without the employment of the feeding networks. Unfortunately, microstrip RA implementations feature narrow bandwidths, and are severely affected by losses. A considerably improved performance can be achieved for RAs involving grounded dielectric layers, which are also easy to manufacture using 3D printing technology. Regardless of the implementation details, a practical bottleneck of RA design is the necessity of independent adjustment of a large number of unit cells, which has to be carried out using full-wave electromagnetic (EM) simulation models to ensure reliability. The associated computational costs are extraordinary. A practical workaround is the incorporation of surrogate modeling methods; however, a construction of accurate metamodel requires a large number of training data samples. This letter introduces an alternative RA design approach, where the unit cells are adjusted using an inverse surrogate model established with a small number of anchor points, pre-optimized for the reference reflection phases. To ensure solution uniqueness, the anchor point optimization involves regularization, here, based on the minimum-volume condition for the unit cell. The presented approach reduces the computational cost of RA design to a few dozens of EM analyses of the cell. Several demonstration examples are provided, along with an experimental validation of the selected RA realization.

Microstrip reconfigurable reflectarray antennas (RRAs) have great potential for advanced systems including satellite communications and the 6th generation (6G) wireless mobile communication networks. However, as a type of microstrip antennas, RRAs generally exhibit an intrinsic issue of narrow bandwidths. This issue is further deteriorated by complicated structures for phase shifting and DC supplying in RRAs. PIN diodes have been used in recent works to control the phases of RRA elements. However, modelling them is still costly and time consuming. In this work, a simple but novel method for modelling PIN diode SMP-1340-040 is developed by using waveguides and modified simulation approaches. Based on the obtained model, a broadband 1-bit unit cell using only one substrate is also proposed, and it achieves a simulated bandwidth of 40.6% and 33.8% for linear and circular polarizations, respectively. The experimental results show an excellent agreement with the simulation, which confirms the accuracy of the proposed PIN diode model. Moreover, the performances of the unit cell demonstrate that it can be used for designing RRAs in bands X and Ku.

This paper presents a novel approach to synthesizing curved reflectarrays using Geometrical Optics (GO). It introduces the concepts of virtual normal and path length shift, which enable a vector-based formulation of the problem that can be solved using ray tracing techniques. The formulation is applied for the design of two different versions of a Dual Bifocal Reflectarray with a parabolic main surface and a flat subreflectarray. The first version aims to enhance the performance of the multibeam antenna by providing a focal ring located at the feed cluster plane. The second version focuses on improving the scanning characteristics of the antenna in the horizontal plane by incorporating two foci. The synthesis procedure yields samples of the path length shift or its derivatives. To reconstruct the phase distribution, an interpolation scheme is employed and described in this paper. Numerical results are presented for both the focal-ring and two-foci configurations, demonstrating the feasibility of this solution for multibeam or scanning satellite antennas operating in the Ka. [ABSTRACT FROM AUTHOR]

This paper presents a feasibility study of a singlylayered dual-band reflectarray for space applications. The data links should operate simultaneously at K-band downlink frequency band 17.7-20.2 GHz with left-hand circular polarization (LHCP) and at Ka-band uplink frequency band 27-30 GHz with right-hand circular polarization (RHCP). The main aim is to present how a reflectarray can be designed so as to allow reconfigurability of its radiation pattern, especially in terms of beam steering to two different directions. The design is automated by means of a computational tool developed in MATLAB environment interfaced with the electromagnetic simulator CST Studio Suite by means of Visual Basic scripts. Simulation results are presented to demonstrate the efficiency of the proposed computational tool and reconfiguration strategy. [ABSTRACT FROM AUTHOR]

This paper presents the design of two passive shaped-beam reflectarrays acting as passive intelligent reflecting surfaces (IRSs) to enhance 5G millimeter-wave coverage in the 27.2–28.2 GHz band. The reflectarray panels have been designed to generate a broadened and deflected beam in dual-linear polarization (horizontal and vertical). The reflectarray cell provides a robust performance under incidence angles of up to 50°, with more than 360° of phase variation range. Phase-only synthesis based on the generalized intersection approach has been applied to obtain the phase distribution on each reflectarray panel, so that their radiation patterns comply with the beamwidth and pointing requirements of the scenario under study. The two reflectarrays show a stable performance in the 27.2–28.2 GHz band in terms of gain, side-lobe level, and cross-polarization. The results confirm the potential of this technology to implement passive low-cost IRSs that will contribute to improve millimeter-wave coverage in 5G wireless networks. [ABSTRACT FROM AUTHOR]

Application demand for faster data rates is driving the need for wider operating bandwidth of future 5G/6G communication systems which in turn poses stringent requirements on the design of suitable antennas. A candidate antenna that can support 5G/6G systems are reflectarrays (RAs) due to their numerous potentials, such as high gain, beam shaping, beam scanning, reconfigurability and multi-beam characteristics. However, reflectarrays are usually limited by their narrowband characteristics. Hence, this work examines the state of the art of wideband reflectarrays. Wideband reflectarrays are reviewed and categorized according to four wideband phase tuning mechanisms. The bandwidth is reviewed and compared both from a unit cell and reflectarray system perspective with emphasis on the gain-bandwidth performance. Different wideband unit cell geometries are covered and grouped by the wideband phase tuning approach. The effect of each wideband phase tuning approach on the gain-bandwidth RA performance is then analyzed by considering the operating frequency, the reflection phase range, the substrate structure and material, the aperture size, the aperture efficiency, the focal distance, the cross-polarization performance as well as the gain and side lobe levels. Finally, the phase tuning approaches are compared against each other, and guidelines are provided for designing reflectarrays with wide gain-bandwidth.

This work introduces an extremely low profile ( $0.4\lambda _{high}$ ) planar ultra-wideband dual-polarized reflectarray. The unit-cell structure of the array is modular in nature, and without any electrical connection between adjacent unit-cells. The array uses tightly coupled dipoles arranged in an egg-crate fashion connected with true-time-delay lines. This array provides the required phase in the highest ever reported bandwidth of 5:1 (3 to 15 GHz) with VSWR< 2.5 for a planar reflectarray. The implementation of the delay-lines is done using a sandwich configuration between two conductive planes, which significantly improves the cross-polarization purity of our reflectarray. To validate our design concept, an $18\times 18$ element ( $135\times 135$ mm) reflectarray is designed, fabricated, and measured. The measurements exhibit excellent agreement with the simulations.

Reflectarray surfaces (RASs) can be useful as passive repeaters or intelligent reflecting surfaces (IRSs) in communication networks by providing nonspecular reflection of an incident wave. To provide adequate signal at a given location, the radar cross section (RCS), and therefore physical size, of the RAS needs to be maximized. This inevitably reduces the beamwidth and bandwidth of the RCS pattern, severely limiting their practical implementation. This article considers a shaped reflector profiled as a truncated ellipse that can give a widened “equi-ripple” beam that addresses these problems. It is shown that by careful selection of the phase profile, the beamwidth can be expanded by a factor of 3.5 (or even 7.5 if lower roll-off in the RCS pattern is allowed) with a corresponding increase in the useable bandwidth. The tradeoff is a reduction in the peak RCS. By increasing the physical size of the reflector, this loss of RCS can be compensated for, still resulting in at least 1.8 times the beamwidth of a flat reflector. The shaped reflector can be realized as an RAS using a closed-form expression. A typical design at 28 GHz is considered. In principle a 22 $\times22$ , $0.4\lambda $ spaced array offers illumination from 40° to 50° over 26–32 GHz, considerably better than the unshaped beam. [ABSTRACT FROM AUTHOR]

This communication proposes a novel unit cell for the design of dual-band dual-circularly polarized reflectarrays for space communications. The main advantage of the proposed cell is the use of one single layer for the antenna fabrication, hence yielding lower costs and fabrication with lower complexity in comparison to multilayer antennas. The proposed cell is used to design a dual-band dual-circularly polarized reflectarray with widely separated bands. Due to the physical symmetry, it provides very good polarization characteristics. The antenna performance is validated by far-field measurements and very good agreement between simulated and measured results has been verified. [ABSTRACT FROM AUTHOR]

In this article, a generalized macromodeling approach is presented to simulate complex electromagnetic (EM) surfaces consisting of unit cells with connected conductors. Macromodels of each unit cell are produced by applying the equivalence principle on fictitious surfaces encapsulating them. Unit cells often consist of multiple dielectric layers and conductor traces, featuring multiscale structures. Challenges arise when a current-carrying conductor trace traverses the fictitious surface. Hence, a new method based on half Rao–Wilton–Glisson basis functions is proposed to accurately ensure the continuity of the surface currents and avoid singularities at the intersections. The accuracy of the proposed approach is validated by comparing the results with commercial solvers for different EM surfaces. [ABSTRACT FROM AUTHOR]

In this paper, a dual circularly-polarized multilayer reflective surface (MRS) based on loaded ring-slots for reflectarray applications is presented. The MRS comprises a wideband multilayer circular polarizer cascaded with a multilayer reflective screen with independent phase shifting properties for the two orthogonal linearly polarized components. The first polarization conversion is accomplished by a four-layer polarizer based on periodic arrays of bisected split rings that converts two incident circularly-polarized waves, one left-handed (LHCPW) and other right-handed (RHCPW), into two linearly polarized waves with orthogonal polarization planes. These two waves can be phase-shifted independently by a periodic two-layer array of specially designed reflective elements. Each element consists of a ring-slot resonator loaded with two pairs of reactances orthogonally located that can be varied to obtain two linear reflection phase tapers along the array. These reflected waves are then transformed back by the polarizer into two circularly polarized waves traveling into the desired directions. To validate the proposed approach, a six-layer prototype operating at 32 GHz that provides reflection elevation and azimuthal angles for the RHCPW at 22° and 180°, respectively, and reflection elevation and azimuthal angles for the LHCPW at 18° and 0°, respectively, has been designed, fabricated, and experimentally verified.

Lightweight, low-cost metasurfaces and reflectarrays that are easy to stow and deploy are desirable for many terrestrial and space-based communications and sensing applications. This work demonstrates a lightweight, flexible metasurface platform based on flat-knit textiles operating in the cm-wave spectral range. By using a colorwork knitting approach called float-jacquard knitting to directly integrate an array of resonant metallic antennas into a textile, two textile reflectarray devices, a metasurface lens (metalens), and a vortex-beam generator are realized. Operating as a receiving antenna, the metalens focuses a collimated normal-incidence beam to a diffraction-limited, off-broadside focal spot. Operating as a transmitting antenna, the metalens converts the divergent emission from a horn antenna into a collimated beam with peak measured directivity, gain, and efficiency of 21.30, 15.30, and -6.00 dB (25.12%), respectively. The vortex-beam generating metasurface produces a focused vortex beam with a topological charge of m = 1 over a wide frequency range of 4.1-5.8 GHz. Strong specular reflection is observed for the textile reflectarrays, caused by wavy yarn floats on the backside of the float-jacquard textiles. This work demonstrates a novel approach for the scalable production of flexible metasurfaces by leveraging commercially available yarns and well-established knitting machinery and techniques., (© 2024 Wiley‐VCH GmbH.)

We propose a multilayer unit cell consisting of Minkowski fractal-shaped reflector with aperture coupled phasing stubs to obtain a broad phase range for reflectarray antenna with smaller unit cell size and interelement spacing compared with some other studies in the literature. In the study, simulations are conducted using high-frequency structure simulator (HFSS) program with Floquet Port incidence. A unit cell with two cycles of phase range and very low reflection loss is designed. About 21.9% shrinkage is achieved in patch surface area using Minkowski fractals. Subsequently, the proposed unit cell is used to design and fabricate a full-scale 221-element reflectarray antenna. At 10 GHz, the simulation results are compared with the measured data and a good agreement is observed. [ABSTRACT FROM AUTHOR]

A simple, low-cost, linearly polarized reconfigurable reflectarray surface (RAS) is presented that can provide beam steering over a wide range of angles in one plane. The results for a prototype design demonstrated beam steering from 35° to 60° at 5.5 GHz. Simple equations describing the beam steering angle and overall size for a minimum radar cross-sectional area (RCS) are presented that aid the system designer. The concertina RAS can be manufactured using screen-printing techniques making this potentially a low-cost product that can meet the needs of widespread deployment needed by wireless systems. A sample design using an A2-sized sheet of paper increased a 5.5 GHz signal by 20 dB, eliminating a “dead spot” in the laboratory. [ABSTRACT FROM AUTHOR]

We present the design and proof-of-concept demonstration of a dual-band reflectarray antenna capable of generating two beams at $X$ - and $Ku$ -bands, whose directions of maximum radiation can be set independently of each other. The reflectarray uses dual-band polarization-rotating (PR) unit cells with 1 bit phase quantization. The proposed unit cell provides independent phase shifts at two frequency bands by controlling a cluster of two orthogonal dipoles to operate as either +90° or −90° reflective polarization rotators. Two dipole clusters are interleaved in a unit cell and used to achieve dual-band operation. Simulation results of a unit cell designed to operate at $X$ - and $Ku$ -bands demonstrate independently controlled, dual-band PR operation over 16.1% and 20% bandwidths for the lower and higher bands, respectively. The dual-band unit cells were used to construct three different static reflectarray prototypes demonstrating the different ways where such independent phase control at the two bands of a dual-band reflectarray antenna may be advantageous. The three static reflectarray prototypes were simulated, fabricated, and experimentally characterized. Simulation and measurement results of these prototypes agree well and demonstrate independent phase shift control at the $X$ - and $Ku$ -bands over a relatively wide field of view without exciting grating lobes. [ABSTRACT FROM AUTHOR]

In this article, a new subwavelength element is introduced into the broadband folded reflectarray antenna (FRA). The element comprises a rectangular split‐ring resonator with two slits and a square patch located in the center of the rectangular ring. It can achieve superior cross polarization conversion (CPC) performance from 16.2 to 26.4 GHz with 1 dB bandwidth of 45.4%, and high orthogonal polarization isolation. Furthermore, changing the positions of two splits of the element can achieve two discrete reflection phases (0° and 180°) with the high CPC efficiency and angular stability. To verify the feasibility, an FRA using the digitally quantized phase distribution method is designed and measured at 22 GHz. The measured results show that the 1 dB gain bandwidth of the proposed FRA is 30.8%, and the maximum aperture efficiency is 15.4%. This superior performance is comparable with the existing FRAs. [ABSTRACT FROM AUTHOR]

This article deals with investigations of slot reflectarray antennas constituted by composite panels and optimized for milling manufacturing. It is shown that a certain combination of the unit-cell geometry parameters may lead to the gain degradation. Analysis of the unit cell shows that this results from the parallel-plate modes excitation. The Floquet circle diagram is used to define conditions for the excitation of these modes. Examples of field plots in the unit cell are given. Theoretical data have been verified by experimental investigations. Presented results allow us to choose proper geometry parameters of the unit cell for slot reflectarray antennas at the initial stage of the development. Some slot reflectarray antennas prototypes are considered as well. [ABSTRACT FROM AUTHOR]

An independently controllable dual-beam reflectarray antenna is presented using a broadband dual-polarized single-layer 1 bit unit cell. The unit cell independently provides two-state phase compensation for two orthogonally linearly polarized waves. The 180° reflective phase difference between the two states is achieved by tuning the magnetic resonance of State 0 and the electrical resonance of State 1. With its two resonances close to each other, the unit cell has a reflective phase difference of 180° ± 20° between two states over a broad bandwidth of 27.2–51.1 GHz. The cross-polarization levels of below −30 dB ensure the high isolation between two polarizations. Using the proposed unit cell, a fixed dual-beam reflectarray antenna is designed and excited by a dual-polarized horn to show the ability of independently controlling two orthogonally linearly polarized waves. At 33 GHz, the beams direct to 20° and −15° for the feeding of horizontally and vertically polarized ports, respectively. The 1.5 dB gain bandwidth is greater than 20% for both polarizations. The proposed dual-polarized reflectarray antenna proves that, for two orthogonally linearly polarized incident waves, the independently controllable fixed dual beams can be realized using the 1 bit phase compensation and single-layer structure. [ABSTRACT FROM AUTHOR]

We propose a new topology for printed circuit board metagratings (MGs) for manipulation of electromagnetic waves at microwave frequencies. By interleaving two single-band segmented gratings (SGs), a composite device capable of performing dual-band operation is realized. The constituent SGs are designed independently, meaning the two operating frequencies need not be harmonically related. The SGs are shielded from one another through inclusion of via fences which suppress near-field coupling. They are each engineered to be inactive within the other’s operating band, which helps retain their individually encoded functionalities. Using the proposed topology, a dual-band MG that performs perfect anomalous reflection of plane waves at 10 and 15.11 GHz is designed. The device is verified both numerically and experimentally. [ABSTRACT FROM AUTHOR]

A novel wideband, multifunctional space-fed planar array antenna is proposed in this article to independently control forward/backward beams. A novel four-layer polarization-dependent unit cell is introduced as the phasing element. A generalized-scattering-matrix (GSM)-based network model is developed to evaluate the element performance and optimize the element structure. Then, a system-level analysis in terms of source feed performance, antenna configuration, and efficiency factors are demonstrated. To verify the design concept, a $13\times 13$ -element ($195 \text {mm}\times 195 \text {mm}$) antenna prototype is designed, fabricated, and tested. The measured realized gains of the reflectarray functionality and transmitarray functionality at 10 GHz are 24 dBi with 18.6% 1 dB fractional gain bandwidth and 23.5 dBi with 22.6% 1 dB fractional gain bandwidth, respectively. Moreover, an additional experiment is implemented to verify the simultaneously bidirectional capability of the proposed antenna. Measured results match well with those of simulation, revealing potential for bidirectional wireless communication applications. [ABSTRACT FROM AUTHOR]

Controlling the phase and amplitude of light emitted by the elements (i.e., pixels) of an optical phased array is of paramount importance to realizing dynamic beam steering for LIDAR applications. In this paper, we propose a plasmonic pixel composed of a metallic nanoantenna covered by a thin oxide layer, and a conductive oxide, e.g., ITO, for use in a reflectarray metasurface. By considering voltage biasing of the nanoantenna via metallic connectors, and exploiting the carrier refraction effect in the metal-oxide-semiconductor capacitor in the accumulation and depletion regions, our simulations predict control of the reflection coefficient phase over a range $>330^{\circ }$ with a nearly constant magnitude. We discuss the physical mechanism underlying the optical response, the effect of the connectors, and propose strategies to maximize the magnitude of the reflection coefficient and to achieve dual-band operation. The suitability of our plasmonic pixel design for beam steering in LIDAR is demonstrated via 3D-FDTD simulations. [ABSTRACT FROM AUTHOR]

Reconfigurable antennas allow to meet the increasing demands of modern RF communication systems for reconfiguration capabilities, such as beam-steering, multi-band operation, polarization flexibility or frequency agility. Active reflectarrays may represent a valuable solution to satisfy the above tasks. This paper reviews several experimental implementations of reconfigurable reflectarray designs developed in recent years. The paper describes the approaches adopted in the realization of active reflectarray designs, mainly focusing on their bandwidth performances. Future challenges in the design of wideband reconfigurable reflectarrays are also outlined.

The future adaptability of reflectarray antenna requires a thorough investigation of its main conventional features for expected improvements. Its existing design featuring at microwave and millimeterwave frequencies can be considered as a basic platform for further studies. In this paper, a thorough review of reflectarrays on some selected areas is presented. Its design implementations involving gain and efficiency improvement are discussed in details. Various design approaches have been critically analyzed at the unit cell and full reflectarray levels for a plausible enhancement in the featured parameters with 5G compatibility.

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

The full-wave simulation of complex electromagnetic (EM) surfaces, such as reflectarrays and metasurfaces, is a challenging problem. In this article, we present a macromodeling approach to efficiently simulate complex EM surfaces composed of PEC traces, possibly with fine features, on a finite-sized multilayer dielectric substrate. In our approach, we enclose each element of the structure with a fictitious surface. By applying the equivalence principle on each surface, we derive a macromodel for each element of the array. This macromodel consists of a linear operator that relates the equivalent electric and magnetic current densities introduced on the fictitious surface. Mutual coupling between the elements of the structure is captured by the equivalent current densities in a fully accurate way. The crux of the proposed technique is to solve for equivalent current densities on the fictitious surface instead of directly solving for the actual current densities on the original scatterer. When simulating complex surfaces, this approach leads to fewer unknowns and better conditioning. We also propose a rigorous acceleration algorithm based on the fast Fourier transform to simulate electrically large surfaces. Numerical results demonstrate that the proposed approach is significantly faster and requires less memory than commercial solvers based on the surface integral equation method while giving accurate results. [ABSTRACT FROM AUTHOR]

In this article, a $7\times 7$ reconfigurable reflectarray operating at X- band is proposed and experimentally verified. The reflectarray consists of linearly polarized, dual-resonance, tunable unit cells fabricated on a single layer. Reconfigurability is achieved by loading each dual-resonance unit cell with four varactors; the two resonances provide a phase range greater than 360°. The unit cell design utilized in this reflectarray is analyzed using full-wave Floquet simulations. A biasing network supporting individual biasing of each array element is designed, allowing beamsteering in E-, H-, and diagonal planes. The proposed reflectarray is evaluated using both full-wave simulations and measurements. To facilitate measurements, a fused filament deposition 3-D printer is used to fabricate an antenna mounting fixture using micrometer stages to make fine adjustments for the final alignment. A measured gain of 15.03 dBi, 3 dB gain fractional bandwidth of 7.81%, and continuous beam scanning are demonstrated in multiple planes from −50° to +50° at 10.1 GHz. [ABSTRACT FROM AUTHOR]

This article concerns a novel solution for folded reflectarray antennas which makes use of a curved (spherical) polarizer. The proposed solution provides a high gain and stable performances on a large bandwidth. A gridded substrate is also employed to minimize the dielectric losses in each reflectarray element, allowing the use of low-cost dielectric materials. Furthermore, 3-D printing technology has been used to manufacture both the polarizer and the reflectarray substrate. A linearly polarized, 28 dBi gain, Ku-band, entirely plastic prototype has been designed, manufactured, and tested. Measurements confirm the feasibility of the proposed solution and show its good performances (54% aperture efficiency and 1 dB down gain bandwidth of about 17%). [ABSTRACT FROM AUTHOR]

The advancement in the current communication technology makes it incumbent to analyze the conventional features of reflectarray antenna for future adaptability. This paper thoroughly reviews the design and experimental features of reflectarray antenna for its bandwidth improvement in microwave and millimeter wave frequency ranges. The paper surveys the fundamental and advanced topologies of reflectarray design implementations, which are needed particularly for its broadband features. The realization of its design approaches has been studied at unit cell and full reflectarray levels for its bandwidth enhancement. Various design configurations have also been critically analyzed for the compatibility with the high-frequency 5G systems.

This letter presents a new approach for the enhancement of the axial ratio (AR) of a single-layer circularly polarized reflectarray antenna based on a circular microstrip patch with phase delay-line stubs unit cell. The AR improvement is achieved by inserting insets around the two stubs, changing the orientation of one of them and using a mirror symmetry arrangement. Two prototypes have been designed, fabricated, and tested to proof the proposed concept in K-band. A good agreement has been obtained between numerical simulations and experimental results. The measured results confirm a remarkable AR improvement with values below 1 dB and 3 dB gain and AR bandwidths larger than 23.7%. [ABSTRACT FROM AUTHOR]

This paper presents a dual-polarization reflectarray unit cell for wideband applications based on stacked Jerusalem crosses with a quarter-wavelength cell period. While unit cells with reduced interelement spacings can suffer from a reduction in phase range, the proposed cell exhibits a phase range of over 500° while maintaining a very independent response to two orthogonal linear polarizations. The unit cell is then integrated with a linear-to-circular polarizer to form a low profile fully planar structure which facilitates independent dual-circular polarization control using a modular design approach. Two prototypes, sized $13.3\lambda _{0}$ by $19.9\lambda _{0}$ at 20.5 GHz, are fabricated and measured, experimentally demonstrating the proposed concepts. [ABSTRACT FROM AUTHOR]

A dual-band ring-focus reflector antenna with a reflectarray subreflector is proposed in this letter. Reflectarray elements present rotationally symmetric structure and a phase range of approximately 360° in the two frequency bands simultaneously. Parabolic reflector is chosen as the main reflector, and a polygonal reflectarray aperture consisting of 137 elements is designed to emulate a metal subreflector. A ring-focus reflector prototype with subreflectarrays was fabricated and measured. The simulated and measured results of the reflector antenna demonstrate a good availability of the design method for utilizing subreflectarrays into the ring-focus reflector antenna, and a good dual-band performance is shown in gain and bandwidths. [ABSTRACT FROM AUTHOR]

This letter proposes an efficient design process to reduce the cross polarization of linear-to-circular reflection polarizers illuminated by practical feeds. In particular, we propose a two-step process, where first a geometrical optimization of the unit cell is applied along one plane of the reflector, followed by a progressive rotation of the unit cell in the orthogonal plane. An offset flat polarizer comprised of dipole unit cells fed by a standard gain horn has been used to illustrate the process. Significant improvements in cross-polarization discrimination are demonstrated by simulation. Two breadboards have been manufactured, and their response is compared in order to demonstrate the validity of the design process. Good agreement with measurements is observed corroborating the proposed technique. [ABSTRACT FROM AUTHOR]

We propose a unit cell consisting of Minkowski fractal with double stubs to attain a broad phase range for the reflectarray antenna. In this study, single stub for Minkowski fractal and double stubs with orthogonal symmetry are simulated using HFSS™ program with Floquet Port incidence. It is observed that the single stub causes higher cross polarization level compared to the double orthogonal stubs. Simulation results are supported by the experimental data obtained from the measurements using waveguide setup. As a result, a broad phase response, better reflection loss, and 10.9% shrinkage in patch size are obtained using double stubs with orthogonal symmetry. Subsequently, the proposed unit cell is used to design and fabricate a full-scale 221 element reflectarray antenna, which may be used, particularly, in aeronautical and space applications. At 10 GHz, simulation results are compared with the measured data, and good agreement is observed. [ABSTRACT FROM AUTHOR]

In this paper, we report the design and realization of 2-D focus scanning of the reflected beam by exploiting the frequency dispersion characteristic of reflectarrays operating at terahertz (THz) frequencies. In the first design, we choose four focal points on a circular path at four different frequencies ranging from 0.225 to 0.3 THz and 2-D beam scanning in the focal plane is achieved as frequency increases. To increase the scanning area, we design a dual-band reflectarray and 1-D scanning is achieved in each of the operating bands with different focal positions along the direction orthogonal to the scanning. The proposed reflectarrays are fabricated and their 2-D focus-scanning abilities are measured and there are good agreements between the simulation results and the measurements. The proposed designs demonstrate and expand further the potential applications of reflectarrays in fast THz imaging and detection. [ABSTRACT FROM AUTHOR]

The method of moments (MoM) in the spectral domain is used for the analysis of the scattering of a plane wave by a multilayered periodic structure containing conducting concentric split rings in the unit cell. Basis functions accounting for edge singularities are used in the approximation of the current density on the split rings, which makes it possible a fast convergence of MoM with respect to the number of basis functions. Since the 2-D Fourier transforms of the basis functions cannot be obtained in closed-form, judicious tricks (controlled truncation of infinite summations, interpolations, etc.) are used for the efficient numerical determination of these Fourier transforms. The implemented spectral domain MoM software has been used in the design of a circularly polarized reflectarray antenna based on split rings under the local periodicity condition. The antenna has been analyzed with our spectral domain MoM software, with CST and with HFSS, and good agreement has been found among all sets of results. Our software has proven to be around 27 times faster than CST and HFSS. [ABSTRACT FROM AUTHOR]

This article describes a circularly polarized 2 × 2 microstrip antenna array with corporate feeding to be used at K‐Band (18.7‐19.2 GHz) as a reflectarray feed. A design approach is proposed for the improvement of axial ratio and impedance bandwidths of circularly polarized microstrip antenna arrays with sequential rotation. A parametric analysis is also proposed to evaluate accurately the array phase center position. An array prototype has been designed, fabricated, and tested. The good agreement obtained between simulation and experimental results provides validation of the design approach and proof of the proposed concept. [ABSTRACT FROM AUTHOR]

In fast Fourier transform (FFT)-based iterative methods for electromagnetic analysis of planar structures, the convolution between Green’s function (GF) and the basis functions is carried out by a product in the spectral domain. In layered media, the GF is known analytically but exhibits singularities in the spectral domain, giving rise to numerical inaccuracy when processed by a direct FFT. We propose a direct spectral approach where the convolution is carried out with due account for the presence of a singular kernel. Using Contour-FFT, the integration contour is deformed and the spatial convolution is expressed as a rapidly converging series of FFTs. We also introduce a novel inverse Contour-FFT operator required for the process. As other FFT-based methods, the short-range interactions are corrected using a precomputed sparse operator, to which we propose an implementation compatible with the Contour-FFT. We control the accuracy of the method with a simple scheme that adapts the method’s parameters to the problem at hand. Several practical numerical examples demonstrate the efficiency and accuracy of the method for the analysis of large nonregular printed structures. [ABSTRACT FROM AUTHOR]

This paper is concerned with reflectarray antenna design with multiple unit cells in order to enhance the gain at the design frequency, while keeping an acceptable bandwidth to work for 5-G mobile base station applications. The design is based on five unit cells. The design begins with an investigation of the phase responses of all unit cells. It is required to choose a unit cell that can span 360° with linear characteristics. Unfortunately, none of the unit cells has perfectly linear phase characteristics. Each of them has a limited linear phase region. The proposed reflectarray design method selects the most linear region from each phase curve for selecting the appropriate unit cell with the appropriate size for each required phase using a phase gradient approach. With this approach, piece-wise linear phase characteristics are adopted for the design of the reflectarray to enhance the gain at the design frequency. [ABSTRACT FROM AUTHOR]

An innovative strategy based on an advanced statistical learning method is introduced to efficiently and accurately predict the electromagnetic response of complex-shaped reflectarray elements. The computation of the scattering coefficients of periodic arrangements, characterized by an arbitrary number of degrees of freedom, is first recast as a vectorial regression problem and then solved with a learning-by-example strategy exploiting the ordinary kriging paradigm. A set of representative numerical experiments dealing with different element geometries is presented to assess the accuracy, the computational efficiency, and the flexibility of the proposed technique also in comparison with state-of-the-art machine learning methods. [ABSTRACT FROM AUTHOR]

For decades, the design of reflectarray antennas followed a unified strategy of selecting a certain unit cell for the whole design. After that, the dimensions or orientations of this unit cell are changed to achieve the required phase shift at each position on the reflectarray surface. This strategy requires a 360° span of the phase characteristics of the selected unit cell versus a control parameter. In addition, it requires maximal linearity of the phase characteristics of the unit cell. This paper considers a different and more flexible strategy for the design of reflectarrays. This strategy is based on switching between unit cells to make use of the regions of the characteristic phase curves of best linearity for each unit cell. With this strategy, we can use unit cells with similar polarization, and unit cells that do not span 360° in phase characteristics in the design process of the same reflectarray. The single criterion for switching between unit cells is the maximal linearity of the phase characteristics of the unit cell at the required phase. This strategy guarantees maximization of the gain, and minimization of the side-lobe level (SLL) at the design frequency. The proposed strategy is validated for the design of a reflectarray antenna to work at 28 GHz using five different unit cells for possible 5G applications. The simulation results reveal the feasibility of the proposed strategy for achieving high gain and low SLL at 28 GHz. [ABSTRACT FROM AUTHOR]

Abstract: The development of flat, compact beam‐steering devices with no bulky moving parts is opening up a new route to a variety of exciting applications, such as LIDAR scanning systems for autonomous vehicles, robotics and sensing, free‐space, and even surface wave optical signal coupling. In this paper, the design, fabrication and characterization of innovative, nonvolatile, and reconfigurable beam‐steering metadevices enabled by a combination of optical metasurfaces and chalcogenide phase‐change materials is reported. The metadevices reflect an incident optical beam in a mirror‐like fashion when the phase‐change layer is in the crystalline state, but reflect anomalously at predesigned angles when the phase‐change layer is switched into its amorphous state. Experimental angle‐resolved spectrometry measurements verify that fabricated devices perform as designed, with high efficiencies, up to 40%, when operating at 1550 nm. Laser‐induced crystallization and reamorphization experiments confirm reversible switching of the device. It is believed that reconfigurable phase‐change‐based beam‐steering and beam‐shaping metadevices, such as those reported here, can offer real applications advantages, such as high efficiency, compactness, fast switching times and, due to the nonvolatile nature of chalcogenide phase‐change materials, low power consumption. [ABSTRACT FROM AUTHOR]