Shenheng Xu

A programmable metasurface with dynamic polarization, scattering and focusing control.

Diverse electromagnetic (EM) responses of a programmable metasurface with a relatively large scale have been investigated, where multiple functionalities are obtained on the same surface. The unit cell in the metasurface is integrated with one PIN diode, and thus a binary coded phase is realized for a single polarization. Exploiting this anisotropic characteristic, reconfigurable polarization conversion is presented first. Then the dynamic scattering performance for two kinds of sources, i.e. a plane wave and a point source, is carefully elaborated. To tailor the scattering properties, genetic algorithm, normally based on binary coding, is coupled with the scattering pattern analysis to optimize the coding matrix. Besides, inverse fast Fourier transform (IFFT) technique is also introduced to expedite the optimization process of a large metasurface. Since the coding control of each unit cell allows a local and direct modulation of EM wave, various EM phenomena including anomalous reflection, diffusion, beam steering and beam forming are successfully demonstrated by both simulations and experiments. It is worthwhile to point out that a real-time switch among these functionalities is also achieved by using a field-programmable gate array (FPGA). All the results suggest that the proposed programmable metasurface has great potentials for future applications.

A Single-Layer Dual-Band Circularly Polarized Reflectarray With High Aperture Efficiency

A single-layer dual-band circularly polarized reflectarray antenna has been designed, fabricated, and tested for Ka-band satellite communications. The reflectarray antenna phasing element is composed of a concentric split-ring, in combination with a modified Malta Cross, where the technique of varying rotation angle and element size has been utilized to compensate the phase delay at 20 and 30 GHz, respectively. All the element configurations have been optimized to reduce cross-polar reflection. The aperture field method has been used to predict the reflectarray radiation performance, such as gain, radiation pattern, and cross-polarization level. A reflectarray with a circular aperture of 420 mm in diameter has been designed, manufactured, and tested for verification. A planar near-field measurement setup has been utilized to measure the reflectarray radiation characteristics. The measured results demonstrate that this dual-band reflectarray has achieved aperture efficiency of 66.5% at 20 GHz and 50% at 30 GHz, respectively.

A Ka-Band Reflectarray Antenna Integrated With Solar Cells

A Ka-band reflectarray antenna integrated with solar cells has been designed, manufactured and tested. The electromagnetic characteristics of solar cells as antenna substrates have been studied and measured. The simulation and measurement results of a reflectarray antenna prototype show good radiation characteristics with measured gain of 26.3 dBi and 1-dB gain bandwidth of 8.75%, while having an optical blockage of 17.6% on solar energy. The proposed technique integrates the two largest components on a satellite platform - solar cells and high gain antennas into one, significantly reducing the volume, mass and cost of satellites.

A Novel Phase Synthesis Approach for Wideband Reflectarray Design

This communication proposes a novel wideband phase synthesis approach, which is able to considerably increase the bandwidth of the reflectarray antenna independent of the element frequency behavior. Specifically, the reference phases at the Ku-band transmitting and receiving frequencies are optimized, simultaneously, to minimize the total phase error of the reflectarray. Simulation and experimental results of reflect-arrays consisting of simple square-ring elements show that a 16.7% measured bandwidth within 1.5-dB gain variation can be achieved by a single-layer design with a thin substrate. The proposed approach is applicable to general reflectarray elements and the phase synthesis process is easy-to-implement compared with other conventional wideband reflectarray designs.

A 1-Bit

An electronically reconfigurable reflectarray antenna (RRA) with 10 × 10 elements is presented with a detailed design procedure for an improved beam-scanning performance. The element, designed at Ku band using a simple patch structure with one PIN diode and two substrate layers, can be electronically controlled to generate two states with 180° phase difference and low reflection loss. A reflectarray prototype is fabricated and experimentally studied for proof of principle. The limitations of the small aperture size are analyzed in detail, and synthetic optimizations of both feed location and aperture phase distribution are used to improve the beam-scanning performance of the prototype. Experimental results agree well with the full-wave simulations, and scan beams within ±50° range are obtained with a maximum aperture efficiency of 17.9% at 12.5 GHz. Consistent scan beams are obtained from 11.75 to 13.25 GHz. Furthermore, the versatile beam-forming capability of the RRA is also demonstrated by a wide-beam pattern synthesis. A fast beam-switching time (12 μs) is theoretically analyzed and verified by the measurement.

10 \times 10

A novel metal-only reflectarray antenna is proposed in this letter. By using a unique unified slot structure, the dielectric substrate commonly applied in conventional reflectarray antennas can be avoided. Various slot elements are investigated, and a prototype reflectarray antenna working at 12.5 GHz is studied for experimental verification. The simulation and measurement results show that good radiation characteristics are achieved by the proposed design. The measured gain is 32.5 dB with 1-dB gain bandwidth of 8.3%, which is comparable to reflectarrays consisting of conventional patch elements. The metal-only structure provides an innovative reflectarray configuration to better withstand the extreme outer space environment and effectively reduce the antenna cost.

Reconfigurable Reflectarray Antenna: Design, Optimization, and Experiment

This paper experimentally demonstrates the use of a microstrip reflectarray as a low-profile planar substitute to a conic section subreflector (hyperboloidal type) in a symmetric dual reflector system at Ku-band. At first, a brief discussion on the simulation and measurement techniques utilized in the paper is provided. A nominal dual reflector Cassegrain system is synthesized through simulations where a feed horn is used to illuminate the hyperboloidal subreflector. Next, a flat metallic subreflector is placed at the subreflector location. This is a critical task as it shows the importance of phase compensation. Due to the flat subreflector, the feed is defocused from the image of the focus and creates phase aberration, leading to beam bifurcation, pattern degradation, and performance deterioration of the dual reflector system. A planar microstrip patch-type subreflectarray is then designed to mimic a hyperboloidal subreflector. Ray tracing is applied to the subreflector-feed system to calculate the phase needed to compensate for the axial defocusing of the feed. A prototype subreflectarray based on the ray-optics approach is fabricated. Radiation pattern measurements and back-projection holographic diagnostics demonstrate that the subreflectarray acts as a hyperboloidal subreflector and restores the antenna performance with a well-defined main beam and low side lobes.

A Metal-Only Reflectarray Antenna Using Slot-Type Elements

A novel transmitarray element consisting of only two layers of modified Malta crosses printed on a dielectric substrate is proposed, and vias are employed to augment the transmission magnitude and enhance its phase shift range. A prototype transmitarray with a circular aperture of 338 mm in diameter is then designed, fabricated, and tested to validate the proposed design. The simulation and measurement results show good radiation characteristics with measured gain of 33.0 dBi at 20 GHz and aperture efficiency of 40%. The proposed element considerably simplifies the complexity of a transmitarray, reducing its thickness, mass, and cost.

Experimental Demonstration of Reflectarrays Acting as Conic Section Subreflectors in a Dual Reflector System

A 100-GHz metal-only reflectarray antenna is designed, fabricated, and tested. The required phase shift is achieved by simply tuning the metal block height, aiming to eliminate dielectric losses at high frequencies. An equivalent circuit model is employed to analyze the element reflection performance. A prototype reflectarray with a 30-mm square aperture is then fabricated and tested using near-field measurement setup. The measured results show an aperture efficiency of 50.1% at 100 GHz, and the measured radiation patterns agree very well with the full-wave simulation results. To compare the radiation performances, a parabolic reflector, a Fresnel zone plate reflector, and an unwrapped reflectarray of same size are also evaluated. The full-wave simulation results demonstrate that the proposed design not only achieves good radiation performance, but also exhibits advantages such as low profile, easy fabrication, and low cost.

A Double-Layer Transmitarray Antenna Using Malta Crosses With Vias

A novel design methodology for single-layer dual-band reflectarray antennas with wide frequency ratios is proposed by exploiting the unique reflection phase properties of Phoenix elements. Full 360° phase ranges at both frequency bands are achieved simultaneously by using only one element set. Compared to conventional approaches that use two sets of elements for dual-band operation, physical and electromagnetic mutual interferences between the elements operating at different frequency bands can be completely avoided. A detailed design procedure for single-layer dual-band reflectarrays with a wide frequency ratio up to 2.5 is presented, and a set of three center-fed dual-band reflectarrays operating at 15/10, 20/10, and 25/10 GHz, respectively, are designed and numerically verified using full-wave simulations. Furthermore, an offset-fed single-layer dual-band reflectarray operating at 20/10 GHz with a circular aperture of 400 mm in diameter is designed, fabricated, and tested for experimental verification. The measured gains are 36.1 dBi with an aperture efficiency of 58.0% at 20 GHz and 30.3 dBi with an aperture efficiency of 61.1% at 10 GHz, respectively. The measured 1-dB gain bandwidth is 9.1% and 14.0% at the upper and lower bands, respectively. Both the simulated and measured results successfully demonstrate the effectiveness of the proposed design methodology.