Reflectarray Configuration Research Articles

Dual-Layer Beamscanning Reflectarray Antenna Operating at Ku-Band

This paper presents a beam scanning electronically reconfigurable reflectarray configuration for Ku-band applications using a single varactor diode. A 15×15 center-fed reconfigurable reflectarray antenna is designed consisting of 225 octagonal shaped unit cells. The proposed tunable element has a unit cell size of 9.8 mm, developed on a 1.575 mm thick Taconic TLY-5 substrate. A single varactor diode is integrated with the tunable element to produce a reflection phase variation of 340° at 14.1 GHz. In this work, both the varactor and biasing circuit are placed beneath the substrate to avoid unexpected reflections, which leads to achieving a pencil beam of 8.1° beamwidth. The simulation results of the reconfigurable reflectarray antenna (RRA) shows good beam-scanning radiation performance of scanning range ±30° and a peak gain of 27.6 dBi. This structure provides a convenient solution for Ku-band distinctive applications like uplink operation in the direct broadcast satellite system, digital video broadcasting, earth exploration satellites, space research satellites, and defense systems.

Enhanced Efficiency and Reduced Side Lobe Level Convex Conformal Reflectarray

In this work, the design of a convex conformal reflectarray (CRA), suitable to be used for high gain on board antenna in mobile communication systems, is presented. The reflector is not planar, as in usual reflectarray configurations, but the re-radiating elements are printed on a surface conformed to a cylinder to mimic a curved surface, such as the fuselage of an airplane, on which the reflectarray could be mounted. To compensate for the loss in efficiency due to the curvature, an ad hoc feed is designed; the results obtained with the simulation of the entire structure and the measurements of its prototype prove the effectiveness of the design procedure and its capability in enhancing the CRA features, in comparison with similar but more conventional solutions.

A Reconfigurable Intelligent Surface at mmWave Based on a Binary Phase Tunable Metasurface

Originally introduced in the early 2010's, the idea of smart environments through reconfigurable intelligent surfaces (RIS) controlling the reflections of the electromagnetic waves has attracted much attention in recent years in preparation for the future 6G. Since reconfigurable intelligent surfaces are not based on increasing the number of sources, they could indeed pave the way to greener and potentially limitless wireless communications. In this paper, we design, model and demonstrate experimentally a millimeter wave reconfigurable intelligent surface based on an electronically tunable metasurface with binary phase modulation. We first study numerically the unit cell of the metasurface, based on a PIN diode, and obtain a good phase shift and return loss for both polarizations, over a wide frequency range around 28.5 GHz. We then fabricate and characterize the unit cell and verify its properties, before fabricating the whole 10 cm x10 cm reconfigurable intelligent surface. We propose an analytical description of the use that can be done of the binary phase RIS, both in the near field (reflectarray configuration) and in the far field (access point extender). We finally verify experimentally that the designed RIS works as expected, performing laboratory experiments of millimeter wave beamforming both in the near field and far field configuration. Our experimental results demonstrate the high efficiency of our binary phase RIS to control millimeter waves in any kind of scenario and this at the sole cost of the energy dissipated by the PIN diodes used in our design.

Dual-Band Dual-Linear Polarization Reflectarray for mmWaves/5G Applications

A dual-band dual-linear polarization reflectarray configuration is developed for future 5G cellular applications. A single layer unit cell including two pairs of miniaturized fractal patches is designed to operate at two distinct frequencies within the Ka-band (27/32 GHz), in a dual-polarization mode. An in-depth analysis of the unit cell behavior is carried out, to demonstrate the total independence between the designed frequency bands and polarizations. The proposed configuration offers a very simply and thin structure, small unit cell sizes, and low losses, while leading to an independent optimization of the phase at each frequency and polarization. A dual-band/dual-polarized reflectarray prototype is designed and tested, thus demonstrating the unit cell flexibility to offer arbitrary beam directions/shapes at each frequency, for both polarizations.

Advanced Multibeam Antenna Configurations Based on Reflectarrays: Providing multispot coverage with a smaller number of apertures for satellite communications in the K and Ka bands

This article presents some recent developments in multiplebeam antennas (MBAs) based on reflectarrays for communication satellites in the Kurz (K) and Kurz-above (Ka) bands. The existing high-throughput satellites commonly employ four reflector antennas to provide cellular coverage that is formed by multiple spot beams in a four-color scheme. Reflectarray antennas are proposed as an attractive solution for the design of novel MBA configurations to produce multispot coverage, with a smaller number of apertures than conventional MBA systems based on reflector technology. Single and dual reflectarray configurations have been considered for the purpose of exploiting their ability to produce independent beams in different polarizations and frequencies.

Time-Modulated Conducting Oxide Metasurfaces for Adaptive Multiple Access Optical Communication

We demonstrate realization of a time-modulated metasurface in near-infrared frequency regime via integration of conducting oxide layers into plasmonic stripe nanoantennas arranged in a reflectarray configuration. The permittivity of conducting oxide layers is modulated in time through modulation of carrier concentration by applying radio frequency biasing signals which leads to generation of higher order frequency harmonics. We rigorously characterize the electro-optical frequency conversion performance of the metasurface. We then exploit the dispersionless angle-independent phase discontinuities on the wavefront of higher order frequency harmonics to achieve dynamic multi-wavelength multi-beam scanning across S, C, and L telecommunication bands via pixelated control over the modulation phase delay. It is established that such time-modulated metasurfaces can be utilized as reflectarray antennas for active multicasting as well as wavelength and angle multiplexing, thus improving optical communication capacity by providing multiple access and integrating several communication channels into a single antenna platform. The role of modulation waveform in the spectral diversity of harmonics is also explored. Specifically, modulation waveform is optimized to realize unicast and broadcast links. Finally, active beam-scanning performance of the time-modulated conducting oxide metasurface is compared with that of its quasi-static counterpart verifying the enhanced bandwidth as well as suppressed side lobes in the time-modulated platform.

Dual-Layer Single-Varactor Driven Reflectarray Cell for Broad-Band Beam-Steering and Frequency Tunable Applications

A dual-layer active reflectarray configuration is proposed for broad-band beam-steering and/or frequency-tunable applications. A unit cell composed by two stacked fixed-size rectangular patches, properly loaded with a single varactor diode, is designed to realize the dynamic phase tuning mechanism. The proposed approach offers wider bandwidths, with respect to the existing varactor-based reflectarray cells, and quite good frequency reconfigurability features, as demanded by several radar or satellite communication applications. An X-band reflectarray cell is fabricated and tested, to prove the effectiveness of the proposed approach, achieving a 318° phase agility within a measured frequency range of about 14.6% with respect to the central design frequency (i.e., 11 GHz). Wideband beam-steering reflectarray designs are demonstrated, showing 1-dB gain bandwidths equal to 9–10%.

A Metal-Only Reflectarray Antenna Using Slot-Type Elements

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.

Radiation Analysis Approaches for Reflectarray Antennas [Antenna Designer's Notebook

This paper compares two basic methods for analysis of the radiation performance of reflectarray antennas. Two different approaches - array theory and aperture field - are first described, and numerical results are then presented for various reflectarray configurations. The advantages and limitations for each method are discussed, and the numerical results are compared with each other, showing very good agreement. Comparison with full-wave simulations showed that these approaches are time-efficient methods that can accurately calculate the reflectarray antenna's pattern shape, main-beam direction, beamwidth, and sidelobe and cross-polarization levels. As such, these methods can be efficient tools for antenna engineers for designing and analyzing reflectarray antennas.

Design of Dual-Reflectarray Antenna for Beam Scanning

This paper describes an architecture for a Ku-band antenna based on a dual flat reflectarray configuration that provides electronic beam scanning within a 13 degree angular range. The antenna configuration presents the simplicity of being implemented with two flat reflectarrays, it provides a compact optics and it can be easily folded and deployed. The main reflectarray emulates a parabolic reflector and the beam scanning is achieved by introducing a phase-control into the elements of the sub-reflectarray. These elements are based on two stacked printed patches aperture-coupled to delay lines, which can be constructed using MEMS switches to provide electronic beam scanning.

Bandwidth Behavior of Closely Spaced Aperture-Coupled Reflectarrays

The bandwidth features of reflectarray antennas are analyzed by examining in detail the phase errors due to the compensation mechanism for spatial phase delays. A bandwidth estimation rule is defined, taking into account the combined effects due to the overall antenna geometry and the frequency response of the single reflectarray element. An aperture-coupled reflectarray configuration with reduced interelement spacing is considered as broadband solution for the implementation of small reflectarrays. A 20 GHz aperture-coupled element is synthesized for the design of a 12 diameter reflectarray, showing a simulated 1 dB gain bandwidth of 23%.

Aperture efficiency analysis of reflectarray antennas

AbstractIn the design procedure of a reflectarray antenna system, the aperture efficiency needs to be first analyzed to forecast the system performance. This article investigates the effects of the reflectarray configuration parameters on the antenna aperture efficiency. A general approach is introduced to calculate the spillover efficiency of a reflectarray with arbitrarily shaped aperture and feed scheme. Meanwhile, the illumination efficiency of the reflectarray is analyzed with a unified set of equations. On the basis of these derivations, parametric studies are performed to provide design guidelines for optimizing the aperture efficiency of reflectarray antennas. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 364–372, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24949

Perturbation Technique to Analyze Mutual Coupling in Reflectarrays

A perturbation technique is described to investigate numerically mutual coupling in reflectarrays. We first define it and then demonstrate that the corresponding perturbation factor has the same meaning as mutual coupling within traditional phased array antennas. Finally the field perturbation approach is applied to a two-element dielectric resonator antenna (DRA) array using finite-difference time-domain (FDTD) modeling. Simulation results show that the proposed method can be used to efficiently analyze mutual coupling in real reflectarray configurations where ports do not exist and cells dimensions are not identical by nature.

Aperture-Coupled Reflectarrays with Enhanced Bandwidth Features

An extensive analysis is performed on the aperture-coupled reflectarray configuration to highlight and quantify the bandwidth enhancement due to the use of reduced inter-element spacings. Bandwidth extension is directly evaluated on the phase curves relative to the reflection coefficient against frequency for different lengths of the tuning line. The operating frequency range computed with the proposed approach is numerically validated on the gain patterns of synthesized reflectarrays and a strong broadband behavior is demonstrated for reflectarrays of moderate aperture dimensions and reduced unit cell size.

TRANSMISSION LINE ANALYSIS OF APERTURE-COUPLED REFLECTARRAYS

A fast analysis of aperture-coupled reflectarrays is presented in this work in terms of transmission line model. The circuital approach is adopted to derive the phase design curve as a function of the current flowing on the equivalent impedance of the single radiating element. Computational costs are drastically reduced with respect to standard full-wave methods. Numerical and experimental validations are discussed on slot-coupled reflectarray configurations working at different operating frequencies.

Development of dual-band circularly polarised reflectarray

The development of a dual-band circularly polarised microstrip reflectarray in Ka-band is presented and various reflectarray configurations with different cell elements are introduced. Among these, reflectarrays with separate crossed dipoles or orthogonal nonintersecting dipoles etched on the same or different substrate interfaces were investigated theoretically and experimentally. Adjusting the lengths of the orthogonal dipoles or arms of the cross dipoles was used to maintain 90/spl deg/ relative phase shift between the orthogonal components of reradiated fields and this gives rise to the realisation of a reflectarray that converts the linearly polarised incident field of the feed into an outgoing circularly polarised field. Various realisations of reflectarrays in terms of cell elements and configuration were designed, fabricated and tested. Measurement results for the final prototype that was of superior performance compared to the other prototypes demonstrated 36% aperture efficiency and axial ratio better than 2.0 dB, for 3% bandwidth on both the Tx and Rx bands.

Scattering by an infinite periodic array of microstrip elements

An analysis of the scattering by an infinite periodic array of microstrip disks is made using a Galerkin solution of a vector integral equation. The solution is examined for convergence and compared with theory and experiment. The solution is used to minimize the loss and maximize the bandwidth of the element in a reflectarray configuration.