Reflectarray Design Research Articles

A Study on a Compact Double Layer Sub-GHz Reflectarray Design Suitable for Wireless Power Transfer

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed.

Gaussian to flat-top beam shaping in an off-axis reflective scenario by a millimeter-wave metasurface.

In this paper, we present a metallic reflectarray for shaping the emitted Gaussian beam of a 100GHz horn antenna in reflective and off-axis mode. The proposed reflectarray is a compact planar surface consisting of a 2D array of unit cells with a thin Rogers 5880 substrate. This reflectarray offers advantages over other beam shapers in millimeter-wave (MMW) imaging, as it generates a flat-top beam in off-axis reflective mode and is straightforward to fabricate. To conduct a feasibility study, we first introduce the 1D reflectarray. The phase profile of the 1D reflectarray is a linear combination of a beam shaping phase profile based on geometrical optics (GO) and a compensating phase profile. The design of the 1D reflectarray involves tailoring the dimensions of the unit cells in one direction. We calculate the scattered field from the 1D reflectarray using the finite element method (FEM) and then determine the generated beam using the Fresnel diffraction integral. Subsequently, we design the 2D reflectarray following the same approach by using a 2D version of the proposed phase profile. The full-wave simulation is employed to calculate the generated beam at a certain distance from the reflectarray. The results reveal the successful generation of a high-quality flat-top beam, showcasing the proposed reflectarray as an evolutionary solution among beam shapers.

Design of a 2-bit Dual-Polarized Reconfigurable Reflectarray With High Aperture Efficiency

Design of a 2-bit Dual-Polarized Reconfigurable Reflectarray With High Aperture Efficiency

Efficient Anomalous Reflector Design Using Array Antenna Scattering Synthesis

A perfect anomalous reflector is designed by employing the receiving and scattering array antenna theory to optimize the scattering characteristics of a planar reflecting surface. For periodic reflectors with a supercell consisting of a relatively few reactively loaded radiating elements, reflection amplitudes into propagating Floquet modes are controlled in an algebraic optimization of the load reactances, avoiding brute-force optimization via electromagnetic simulations. Wide-angle reflectors are numerically designed and compared with the conventional reflectarray designs, showing that the proposed design approach achieves reflection efficiencies higher than the linear reflection phase gradient method in a computationally efficient manner.

Design of Alvarez Beam Scanning Reflectarray With Inversely Proportional Focal Length

In this letter, a beam scanning Alvarez reflectarray (RA) metasurface with its focal length ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> ) inversely proportional to the phase distribution on the Alvarez RA aperture is presented for ±45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> beam scanning coverage and less than 3-dB gain loss. The beam scanning mechanism is based on mechanically tilting the Alvarez RA panel to the desired direction to steer the beam. Compared to a conventional RA where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> is directly proportional to the parabolic phase distribution, the proposed Alvarez RA shows a wider 1-dB and 3-dB gain bandwidth, higher aperture efficiency (AE <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</i> , and wider scanning range with less than 3-dB gain loss. The proposed RA has adopted an Alvarez phase distribution which is a summation of two shifted cubic phase profiles. Pancharatnam- Berry (PB) meta-atoms of sub-wavelength periodicity were utilized to provide the 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> phase range and to enhance the bandwidth of the RA. An Alvarez RA consisting of 38 × 38 PB meta-atoms has been designed, fabricated, and tested for ±45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> beam scan coverage with less than 3-dB gain loss. The simulated and measured results show that the gain of the proposed Alvarez RA metasurface is 29.1 dBi at 19.5 GHz, which corresponds to an AE of 44.2%. The 3-dB gain variation of the Alvarez RA is from 15 GHz to 23.4 GHz, which corresponds to a 3-dB gain bandwidth of 43.7%. The 1-dB gain bandwidth was 27.8% from 17.3 GHz to 22.9 GHz.

Support Vector Regression Models of Reflectarray Unit Cell in a Geometrical 4-D Parallelotope Domain Around a Rectangle of Stability

In this work, surrogate models based on support vector regression (SVR) of a multi-resonant unit cell in a geometrical 4-D parallelotope domain are trained and used in a reflectarray antenna design. The multiple sharp resonances of the unit cell prevent a suitable training process in the whole orthotope defined by the available degrees of freedom (DoF). Thus, a strategy to improve the training process and obtain highly accurate models is devised. It consists in defining a parallelotope around a rectangle of stability, which is in turn defined at a lower dimensionality. The SVR models with four geometrical DoF obtained in this parallelotope are shown to provide highly accurate results for the design of a large contoured-beam reflectarray for space applications. The direct optimization with the surrogate models allows to improve the cross-polarization performance several dB while considerably increasing computational performance. Furthermore, compared to lower dimensionality models, the 4-D models offer better results when applied to wideband and dual-band reflectarray direct optimization.

Structural and Radio Frequency Co-Design and Optimization of Large Deployable Reflectarrays for Space Missions

The structural and Radio-Frequency (RF) design and optimization of a large deployable faceted reflectarray (RA) generating double polarization contour beam are presented in this work. The issue addressed is the thermoelastic stability of large RAs and the impact of the thermoelastic deformation (TED) under transverse thermal gradient on the RA performances. Finite elements TED analysis are conducted on a deployable RA with self-standing structures, demonstrating the detrimental effects of the in-orbit TED impact on the RA performances, estimated to be above 3 dB losses. To this extent, a novel structural solution is proposed, based on the employ of reliable mechanical support capable to mitigate the TED. The mechanical design reorientation is contingent on the RF design reformulation. The proposed novel mechanical and RF co-design concept and methodology allows the conception of a low profile, thermo-structurally stable RA with compliant radiation patterns and high cross-polarization discrimination in the worst-case thermal load. This methodology is based on a direct optimization of nine panels faceted RA composed of advanced high-order Phoenix cells directly optimized to fulfill the contoured beam requirements and by respecting the local periodicity requirements of the layout.

Electronically Controlled Frequency Agile Beam Scanning Reflectarray Antenna with Integrated Control Unit

This paper reports the design, development, fabrication, and testing of a 225-element reconfigurable reflectarray (RRA) antenna with frequency agility and beam steering capabilities. The 15 15 (18.75 cm) RRA operating in the Ku band downlink frequency range (11.8 -12.2 GHz) of fixed satellite services (FSS) produces dual resonances switched between uplink frequency range (15-18 GHz) of FSS and earth exploration satellite range of 9.5-9.8 GHz (X Band). To attain reconfigurable multiple resonances, the unit cell is designed with a Malta cross of varying slot lengths interconnected to a square ring via a PIN diode. In the OFF state of the PIN diode connected between the concentric elements, a phase variation of 360° is obtained at 12 GHz and 9.5 GHz by varying the size of the Malta cross. By increasing the width of the outer ring in the ON state of the PIN diode, a dual resonance is obtained at 12 GHz and 17 GHz with 360° phase agility. The beam scanning is attempted at X band frequency by controlling the capacitance offered by the varactor diode connected between an inductive element and Malta cross. The proposed RRA offers 22.16 dBi, 24.5 dBi and 18.43 dBi simulated gain at 17 GHz, 12 GHz, and 9.5 GHz respectively. The simulated sidelobe levels (SLLs) and cross-polarization levels are -14.7 dB and less than -32 dB respectively. The proposed compound reconfigurable reflectarray befits fixed and mobile satellites, earth exploration satellites, radiolocation, aeronautical radio navigation, and deep space research.

Design and Development of Frequency Agile Reflectarray Antenna

This paper presents the design of a frequency reconfigurable reflectarray with concentric circular rings. The PIN diode connected between a phase delay line and the ring produces reconfigured resonances at 16 GHz and 10.4 GHz. The variation in the size of the concentric rings offer a phase change of 356º during the OFF state of the PIN diode. 360° phase variation in the PIN ON condition is achieved by varying the delay line length. A 225-element centre-fed reflectarray antenna is constructed with square geometry. A simulated gain of 23 dBi is obtained with -17 dB side lobe level and -28 dB cross-polarization level at 16 GHz. In the PIN ON condition, a simulated gain of 22 dBi is obtained with -12 dB side lobe level and -28 dB cross polarization level. This reconfigurable reflectarray finds its applications in space research, satellite communication, and RADAR.

Light-Controlled Large-Scale Wirelessly Reconfigurable Microstrip Reflectarrays

In this article, the concept and design of light-controlled large-scale wirelessly reconfigurable microstrip reflectarrays are proposed. Unlike conventional electrically reconfigurable microstrip reflectarray antennas (RAs) that control the aperture phase distribution by conducting wires for transmitting control signals, the proposed method utilizes light to control the ON- and OFF-state of the integrated positive-intrinsic-negative (p-i-n) diodes wirelessly and binaurally through light-sensitive resistance of photodiodes (PDs). The concept is validated by simulation first, where a 1 bit 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times32$ </tex-math></inline-formula> wirelessly reconfigurable microstrip RA is designed at 10 GHz with a beam-steering range of ±60° for sidelobe levels < −10 dB, marking a record of 1024 elements with a tri-layer configuration. Experimentally, the light-control scheme is further validated by a smaller porotype of 256 elements, where a light-controlled beam steering from 30° to 45° is demonstrated. Compared with conventional wired reconfigurable microstrip RAs, the proposed method resolves the wire-routing complexity on the RA and offers a new possibility for further improving the maximum directivity, upper operating frequency, and the number of independently controllable polarizations of reconfigurable microstrip reflectarrays, paving the way for developing very-large reconfigurable intelligent surfaces (VRIS). Also, the proposed concept provides a new infrastructure for information exchange between light and microwaves.

A Single-Layered Broadband Reflectarray Employing 0.15-Wavelength Elements

A single-layered broadband reflectarray antenna employing 0.15-wavelength elements is proposed and investigated in this letter. The unit cell is constituted by a ring patch inserted with an interior concave arm and arranged in a grid size of 4.5 mm × 4.5 mm, corresponding to only 0.15 wavelength at 10 GHz. Despite such a small grid spacing, a linear phase close to 360° can still be obtained by changing the height of the embedded concave arm, without adjusting the external ring size. A planar reflectarray antenna composed of 2116 unit cells is designed, manufactured, and tested. According to the measured results, the 1 dB gain bandwidth of the reflectarray antenna is 29%, while the peak aperture efficiency is 66%. Besides, satisfactory sidelobe and cross-polarization levels are also achieved. These promising features show a good overall performance of the proposed array and also successfully demonstrate the feasibility of employing 0.15-wavelength element for wideband reflectarray designs.

Reflectarray Design Using a Discrete Dipole Framework

We propose and numerically validate a patch reflectarray modeling approach suitable for small patches that describes each patch as a pair of polarizable magnetic dipoles. We introduce an extraction technique to obtain the effective polarizability of the patch dipoles via full-wave simulations on individual patches, followed by a beamforming design routine valid under weakly scattering configurations. This dipole framework serves as an alternative to the ray tracing model often used in reflectarray designs, in which rays are drawn from the feed point and scattered off of the patch elements. Whereas the ray tracing method solves the design problem in terms of phase delays, the dipole framework presented here has the potential to accurately design and predict beam patterns using a fully dipolar treatment of empirically characterized patches. We illustrate this technique by applying it to two modulation strategies: a variable patch size reflectarray in which the phase can be continuously tuned (grayscale patch response), and a fixed patch size (binary patch response) in which on/off modulation is achieved through selective patch electrical shorting. Methods for incorporating these cases into the dipole design framework are discussed and the results compared to those from full wave simulation.

Microstrip Reflectarray Design for 26 GHz

This paper presents microstrip reflectarray design using variable size unit cell approach for 26 GHz, and investigates the effect of feed antenna distance to the surface. The unit cell structure is made up of a 1.5 mm foam layer (εr=1.37) and a 0.787 mm substrate layer (εr=2.2) between the ground and reflective layers. Two arrays of 14λx14λ in size were designed to reflect the incoming wave in the θ=25º direction; the distance to the feed was 160 mm in one design and 320 mm in the other design. Simulation results show gain of 30.2 dBi for the former and 29.8 dBi for the latter. 3-dB gain bandwidths were 11 % and 14 %, respectively

Analysis and design of terahertz reflectarrays based on graphene cell clusters

In this paper, the graphene cell-cluster is introduced, which is composed of an array of identical unit-cells placed in a geometrical configuration. Such graphene cell-clusters are then used for the realization of a reflectarray. To the best of our knowledge, identical unit-cells in a particular geometrical configuration have already been introduced, but the analytical formulas for this model have not been investigated so far. In this paper, the Fourier-optics and aperture field estimation methods are applied to investigate the effect of cell-cluster dimensions on the generation of specified far-field radiation patterns. Implementing cell-clusters in graphene reflectarrays and similar structures, and also applying the proposed formulas, lead to the simplicity of configuration and enhancing the design accuracy. First, the effect of cell-cluster dimensions on the reflectarray radiation pattern is investigated. Then, a reflectarray composed of graphene cell-clusters is designed. A new configuration of graphene unit-cell composed of two graphene layers is proposed, where a middle layer of metallic patch is inserted. In the common graphene unit-cells, the rate of amplitude variations is quite high and greatly depends on the variation of phase in the proposed unit-cell. However, the amplitude variation is quite smaller than the phase variations.

3D Printed “Kirigami”-Inspired Deployable Bi-Focal Beam-Scanning Dielectric Reflectarray Antenna for mm-Wave Applications

This article presents a state-of-the-art 3-D-printed dielectric reflectarray antenna featuring one-shot deployability and wide-angle beam-scanning ability. The design is enabled by a series of a “kirigami”-inspired two-stage snapping-like element structure that can be retracted by 66% to save space. The prototype is fabricated with a stereolithography (SLA) 3-D printing method with the Formlabs Flexible 80A photopolymer. A bifocal phase distribution method is utilized to optimize the RF performance of the array, realized −30° to −10° and 10° to 30° beam-scanning ability. The outcome of this work demonstrated a high-performance dielectric reflectarray design with ease of fabrication for 5G and satellite communication applications.

Design of Planar and Conformal, Passive, Lossless Metasurfaces That Beamform

A general technique for synthesizing both planar and conformal beamforming metasurfaces is presented that utilizes full-wave modeling techniques and rapid optimization methods. The synthesized metasurfaces consist of a patterned metallic cladding supported by a finite-size grounded dielectric substrate. The metasurfaces are modeled using integral equations which accurately account for mutual coupling and the metasurface's finite dimensions. The synthesis technique consists of three phases: a direct solve phase to obtain an initial metasurface design with complex-valued impedances satisfying the desired far-field beam specifications, a subsequent optimization phase that converts the complex-valued impedances to purely reactive ones, and a final patterning phase to realize the purely reactive impedances as a patterned metallic cladding. The optimization phase introduces surface waves which facilitate passivity. The metasurface is optimized using gradient descent with a semi-analytic gradient obtained using the adjoint variable method. Three examples are presented: a low-profile directly-fed metasurface antenna with near perfect aperture efficiency, a scanned-beam reflectarray design with controlled sidelobes, and a conformal metasurface reflectarray. The far-field and near-field performance of the metasurfaces are verified and the bandwidth and loss tolerance of the metasurfaces are investigated.

A Wideband Circularly Polarized Folded Reflectarray Antenna With Linearly Polarized Feed

The design and implementation of a wideband circularly polarized folded reflectarray antenna (CPFRA) with a linearly polarized (LP) feed antenna is presented in this letter. The subreflector of the proposed CPFRA is in the form of a polarization-sensitive frequency selective surface (FSS) based on the antenna-filter-antenna (AFA) technology other than the traditional polarizing grid. The AFA FSS is designed to convert the LP incident wave into circularly polarized (CP) wave within its passband and reflect the orthogonal LP incident wave over a wide frequency band. Futhermore, the sequential rotation technique is applied in the design of main reflectarray and subreflector to greatly enhance the axial ratio (AR) bandwidth of the CPFRA. An antenna prototype has been fabricated and measured at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band. Good agreement between the measured and simulated results has been achieved by the wideband CPFRA. The measured results show that the maximum antenna gain reaches up to 28.2 dBic at 10.2 GHz with its aperture efficiency of 43.3%. The 3 dB gain frequency band is from 9.1 to 10.6 GHz and the 3 dB AR frequency band from 8.7 to 11.2 GHz, respectively.

Holographic transmitarray antenna with linear polarization in X band

For the first time, we present the design and demonstration of holographic transmitarray antennas (TAs) based on the susceptance (reactance) distribution in this paper. According to the holographic theory, the amplitudes and phases of electromagnetic waves can be recorded on a surface, and then they can be reconstructed independently. This concept is used to design single-beam and multi-beam linearly polarized holographic TAs without using any time-consuming optimization algorithms. Initially, an impedance surface is analyzed for both transmission and reflection modes. As there are differences between the susceptance (reactance) distribution of these modes, a new approach (different from reflectarray designs) is proposed to apply the holographic technique to transmitarray designs. Then, interferograms are described based on the scalar transmission susceptance distribution according to the number and direction of the radiation beams. Subsequently, a transmission metasurface of dimensions equal to 0.26λ0 is hired to design holographic TAs at 12 GHz. Several holograms are designed using the unit cell to verify the proposed method. Finally, as a proof of concept, a linearly polarized circular aperture wideband holographic transmitarray antenna with a radius of 13.3 cm is manufactured and tested. The antenna achieves 12.5% (11.4-12.9 GHz) 1-dB gain bandwidth and 23.8 dB maximum gain, leading to 21.46% aperture efficiency. Furthermore, the antenna achieves 95.94% simulated radiation efficiency mainly due to using subwavelength elements, which becomes possible by applying the holographic technique.

Analysis and Design of an X-Band Reflectarray Antenna for Remote Sensing Satellite System.

This paper presents the analysis and design of an X-band reflectarray. The proposed antenna can be used for a medium Earth orbit (MEO) remote sensing satellite system in the 8.5 GHz band. To obtain a nearly constant response along the coverage area of this satellite system, the proposed antenna was designed with a flat-top radiation pattern with a beam width of around 29° for the required MEO system. In addition, broadside pencil beam and tilted pencil beam reflectarrays were also investigated. The feeding element of the proposed reflectarray antennas is a Yagi–Uda array. The amplitude and phase distribution of the fields due to the feeding element on the aperture of the reflectarray antenna are obtained directly by numerical simulation without introducing any approximation. The required phase distribution along the aperture of the reflectarray to obtain the required flat-top radiation pattern is obtained using the genetic algorithm (GA) optimization method. The reflecting elements of the reflectarray are composed of stacked circular patches. This stacked configuration was found to be appropriate for obtaining a wide range of reflection phase shift, which is required to implement the required phase distribution on the reflectarray aperture. The antenna was fabricated and measured for verification.

Ka-Band Reconfigurable Reflectarrays Using Varactor Technology for Space Applications: A proposed design

In this article, Ka-band reconfigurable reflectarray antennas based on varactor diodes are investigated. Varactor diodes enable high radiation pattern flexibility while maintaining acceptable costs. The design of a dual-band reconfigurable reflectarray based on varactor technology is described in detail. The antenna, considered for a fixed or mobile ground station for satellite telecommunications systems, could be used for several other applications. To demonstrate and validate experimentally the proposed concept, the design of a reduced-sized antenna is presented. The manufacturing and testing of its reconfigurable reflecting surface are then described and discussed. This antenna design could also be considered as a baseline for a data downlink antenna employed on a satellite.