Reflectarray Unit Cell Research Articles

Communication A Novel Systematic Design of High-Aperture-Efficiency 2D Beam-Scanning Liquid-Crystal Embedded Reflectarray Antenna for 6G FR3 and Radar Applications

This communication presents a novel systematic design of a high-aperture-efficiency and 2-D beam-scanning nematic liquid-crystal (LC)-based reflectarray (LCRA) that operates in the sixth-generation (6G) midband (7–24 GHz). Despite a 260° phase range, the maximum aperture efficiency is 35.8% at an aperture dimension (F/D) ratio of 0.58, the highest aperture efficiency at the lowest F/D ratio among LCRAs designed to operate on the mmWave band. The proposed LC-based reflectarray unit cell (LC-RUC) has significantly low reflection loss compared to other LC-RUCs. Also, the bias topology of the proposed LC-RUC makes the LCRA capable of 2-D beam scanning. The beam-scanning range of the proposed LCRA is ±50° on the xoz plane and 0°–65° in the yoz plane at 9.55 GHz. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2 $ </tex-math></inline-formula> patch array antenna is designed as the feed antenna to achieve a small F/D ratio system and ease of optimization. When designing the feed antenna, the number of elements or the element spacing is considered to achieve high feed efficiency. In addition, the fabricated planar feed antenna can be easily integrated with a 3-D printed jig in which the focal length can be adjusted for optimization. The lowest side lobe level (SLL) of the proposed LCRA is −15.5 dB.

K-Band Circularly Polarized Beam Steerable Reflectarray Enabling Internet of Space: Conceptualization and Validation

Low-cost and lightweight CubeSats have opened new possibilities to realize Internet of Space (IoS), a vision that aims to provide global network access, particularly for remote areas. A key challenge for IoS realization is the development of an antenna that can meet the gain, bandwidth, and polarization requirements for IoS while complying with the small form factor of CubeSats. The challenge is further magnified by the need to dynamically reconfigure the antenna’s beam location to maintain connectivity as the satellite orbits. This work addresses these challenges by proposing a beam steerable reflectarray antenna that can potentially be integrated with CubeSats to enable IoS. A novel reflectarray unit cell containing multiple Archimedean spiral arms is designed to support broadband circularly polarized (CP) operation, and its operational principle is discussed in depth. The unit cell provides four states of phase shift that are electronically switchable, allowing the reflectarray to achieve the required aperture phase for the desired beam scan. Representative reflectarray prototypes are designed, fabricated, and measured. CP beam scan up to 60° in the plane of offset across the targeted frequency band of 17.8–20.2 GHz is achieved.

Towards Efficient Reflectarray Digital Twins - An EM-Driven Machine Learning Perspective

The concept of digital twins (DTs) for reflectarray (RA) unit cells (UCs) is discussed and implemented by exploiting electromagnetic-driven machine learning (ML) techniques. Toward this end, several open challenges are addressed, such as the reliability and the effectiveness of using surrogates for modeling different, in terms of descriptors and complexity, UCs, the accuracy in predicting the scattering matrix entries of both single- and dual-polarization elements, the implementation of effective and efficient strategies for the setup of the training set, and the definition of generalized and robust guidelines for the use of popular ML techniques to the problem at hand. Representative results of an extensive numerical validation are presented to assess the performance and the potentialities of DTs when dealing with different RA modeling problems and training sets.

Generalized equivalent circuit model of a split-ring-loaded dipole reflectarray unit cell under TE oblique incidence

Generalized equivalent circuit model of a split-ring-loaded dipole reflectarray unit cell under TE oblique incidence

Three-dimensional accurate modeling of nematic liquid crystal based dipole unit for reconfigurable reflectarray at 100 GHz

In this paper, a three-dimensional accurate modeling of nematic liquid crystal (LC) has been presented for the analysis of reconfigurable reflectarray cells based on LC. Both single-dipole and multiple-dipoles constructed on a LC substrate are designed as the reflectarray unit cell. Considering the inhomogeneous and anisotropic effects, the orientation of the LC molecules at each point of the LC layer involved in the unit cell under the external electrostatic field is obtained by the finite difference numerical modeling method. Utilizing the accurate modeling results of LC, the reflection constants of the reflectarray unit cells have been simulated and also have been compared with that of in the conventional model which usually assumes the LC is homogeneous and isotropic (HOMI). The error of phase range of the unit cell between the two models can exceed 45° in the single-resonant unit cell, and is more than 290° in the multi-resonant unit cell, which will seriously affect the practical application. The permittivity of LC in the unit cells under different applied voltages also has been calculated and given. Moreover, the gain radiation pattern of the reflectarray consisting of the proposed LC based double-dipoles unit cell is simulated in two models. The simulation results show that, in the accurate modeling, the gain and scanning angle range of the reflectarray obtained by the HOMI model change significantly because the phase-shift of the same unit cell for the incident wave is greatly different in the two models, which indicates that the HOMI model can no longer meet the needs of the design of LC based multi-dipoles reflectarray. Therefore, the accurate modeling method needs to be considered and cannot be ignored when studying and designing LC based devices.

Linearly Polarized Millimeter Wave Reflectarray with Mutual Coupling Optimization

This work provides the design and analysis of a single layer, linearly polarized millimeter wave reflectarray antenna with mutual coupling optimization. Detailed analysis was carried out at 26 GHz design frequency using the simulations of the reflectarray unit cells as well as the periodic reflectarray antenna. The simulated results were verified by the scattering parameter and far-field measurements of the unit cell and periodic arrays, respectively. A close agreement between the simulated and measured results was observed in all the cases. Apart from the unit cells and reflectarray, the waveguide and horn antenna were also fabricated to be used in the measurements. The measured scattering parameter results of the proposed circular ring unit cells provided a maximum reflection loss of 2.8 dB with phase errors below 10°. On the other hand, the measured far-field results of the 20 × 20 reflectarray antenna provided a maximum gain of 26.45 dB with a maximum 3 dB beam width of 12° and 1 dB gain drop bandwidth of 13.1%. The performance demonstrated by the proposed reflectarray antenna makes it a potential candidate to be used in modern-day applications such as 5th Generation (5G) and 6th Generation (6G) communication systems.

Fully Metallic Reflectarray for the Ku-Band Based on a 3D Architecture

This document presents the design and manufacture of a reflectarray (RA) antenna for the Ku-band that is based on a fully-metallic 3D architecture. The reflectarray unit cell is formed by a square-shaped waveguide section ending in a short circuit, which is the reflectarray back ground plane. Each cell has the ability of configuring the phase of its own reflected field by means of resonators perforated on the walls of the cell waveguide section. The resonator-based waveguide cell introduces the 3D character to the design. The geometry of the resonators and the size variation introduces the phase behavior of each cell, thus, conforming the radiation pattern of the reflectarray. This design explores the potential of phase value truncation (six states and two states) and demonstrates that proper pattern results can be obtained with this phase truncation.

Liquid-Crystal-Based X-Band Reactively Loaded Reflectarray Unit Cell to Reduce Reflection Loss

This letter presents a novel design of a nematic liquid-crystal (LC)-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band reactively loaded reflectarray unit cell (RLRUC) to reduce reflection loss. The reflection loss of an LC-based reflectarray unit cell (RUC) can be reduced by increasing the thickness of the LC or the superstrate. However, in the conventional RUC, the superstrate thickness has little impact on the reflection loss due to the absence of a contribution to the actual input impedance. The reflection loss can be significantly reduced by adding an additional metallic patch onto the top of the superstrate, which serves as a reactive load. The reflection loss is analyzed by an equivalent circuit model in this letter. For the measurements, a 1 × 2 array of unit cells is introduced. Metallic vias shielding around the unit cell array is embedded into the substrates to substitute for a metallic wall. In addition, a simple bias configuration is achieved by inversely arranging the substrates. The RLRUC achieves a dynamic phase range of 240° with a reflection loss of only 1.5 dB. Compared to earlier work which reported an LC-based RUC that operated on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band, the proposed design achieves extremely low reflection loss.

Analysis of the possibility of using graphene in the design of reflectarray unit cells

Flexible reflectarrays are widely used as deployable antennas in the design of small satellites (weight about 320 kg) to reduce the weight and size characteristics. Modern flexible reflectar-ray antenna use metals as the conductive material. Graphene has unique properties that are suitable for flexible antenna systems - mechanical stability, low specific gravity and cost. This paper is the first to consider the possibility of using graphene as a conductive material in the design of unit cell elements of a reflectarray antenna in the GHz range: a patch element, a patch element with a ring, and a patch element with a delay line. The minimum values of the incident wave amplitude and the phase variation range for each element were -4.08 dB and 327.6 degrees, -19.63 dB and 684.73 degrees, -6.24 dB and 526 degrees, respectively. The comparison of the obtained characteristics of unit cell elements with similar silver elements is carried out. Comparison of the characteristics with the literature analogs showed that the graphene unit cell elements of the reflectarray antenna have satisfactory characteristics.

Electromagnetic Response Prediction of Reflectarray Antenna Elements Based on Support Vector Regression

In this letter, support vector regression (SVR) is used to predict the electromagnetic (EM) response of a complex shaped reflectarray (RA) unit cell. The calculation of the scattering coefficients of passive RA elements with periodic intervals is firstly transformed into a regression estimation problem, and then an analysis model is established by SVR to quickly predict the EM response of the unit cells. To this end, the full-wave (FW) simulation software is used to obtain a set of random samples of the scattering coefficient matrix of the RA antenna unit cell, which is used for SVR training. Under the same conditions, the radial basis function network (RBFN) is also used to predict the EM response of the elements, and the comparison results show the effectiveness and accuracy of the proposed method.

Reconfigurable Reflectarray Antenna: A Comparison between Design Using PIN Diodes and Liquid Crystals

This work presents the design and analysis of active reflectarray antennas with slot embedded patch element configurations within an X‐band frequency range. Two active reflectarray design technologies have been proposed by digital frequency switching using PIN diodes and analogue frequency tuning using liquid crystal‐based substrates. A waveguide simulator has been used to perform scattering parameter measurements in order to practically compare the performance of reflectarray designed based on the two active design technologies. PIN diode‐based active reflectarray unit cell design is shown to offer a frequency tunability of 0.36 GHz with a dynamic phase range of 226°. On the other hand, liquid crystal‐based design provided slightly lower frequency tunability of 0.20 GHz with a dynamic phase range of 124°. Moreover, the higher reflection loss and slow frequency tuning are demonstrated to be the disadvantages of liquid crystal‐based designs as compared to PIN diode‐based active reflectarray designs.

Development of a Pin Diode-Based Beam-Switching Single-Layer Reflectarray Antenna

This paper presents a practical demonstration for the design and development of a switchable planar reflectarray using PIN diodes in the X-band frequency range. Waveguide scattering parameter measurements for the unit cells and far-field measurements of the periodic reflectarrays have been carried out to verify the predicted results. Reflectarray unit cell measurements demonstrated a frequency tunability of 0.36 GHz with a dynamic phase range of 226°. On the other hand, the designed 6 × 6 periodic reflectarray has been shown to achieve beam switching from +6° to −6° with different switching states of PIN diodes. This type of beam switching can be used in satellite communication for specific region coverage.

On the Use of the Angle of Incidence in Support Vector Regression Surrogate Models for Practical Reflectarray Design

A common approach in the literature when obtaining surrogate models of reflectarray unit cells is to include, among other variables, the angles of incidence as input variables to the model. In this work, we use support vector regression (SVR) to compare this approach with a new strategy which consists in grouping the refletarray elements under a small set of angles of incidence and train surrogate models per angle of incidence pair. In this case, the dimensionality of the SVR decreases in two with regard to the former approach. In both cases, two geometrical variables are considered for reflectarray design, obtaining 4-D and 2-D SVRs, respectively. In contrast to the common approach in the literature, the comparison between the 4-D and 2-D SVRs shows that a proper discretization of the angles of incidence is more competitive than introducing the angles as input variables in the SVR. The 2-D SVR offers a shorter training time, faster reflectarray analysis, and a similar accuracy than the 4-D SVR, making it more suitable for design and optimization procedures.

Design and fabrication of a novel single-layer Ka-band reflectarray antenna

AbstractA novel dual-polarization, single-layer reflectarray has been designed and manufactured to operate at receive (20 GHz) and transmit (30 GHz) frequencies for Ka-band terminal antennas. The reflectarray unit cell is composed of several types of resonant elements printed on the upper side of a conductor-backed substrate, which are designed to produce a collimated beam at 20 and 30 GHz in dual polarization. Cross-shaped loops are used to provide the required phases at 20 GHz, while crossed dipoles and modified truncated rings are used to control the phasing at 30 GHz. The resonant lengths of the proposed elements have been adjusted cell by cell by means of a two-dimensional interpolation method to achieve the required phase shift at each frequency. Two different feeds have been used to illuminate the reflectarray at 20 and 30 GHz. The measured gain is 28.02 dBi at 20 GHz and 32.14 dBi at 30 GHz. The measurement results show that the radiation patterns of the designed single-layer reflectarray antenna are in good agreement with those achieved from the simulations.

Reflectarray Antennas for Independent Dual Linear and Circular Polarization Control

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 13.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> by 19.9λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at 20.5 GHz, are fabricated and measured, experimentally demonstrating the proposed concepts.

Phase-Agile Dual-Resonance Single Linearly Polarized Antenna Element for Reconfigurable Reflectarray Applications

A single-layer dual-resonance tunable reflectarray unit cell supporting a single linear polarization and operating at ${X}$ -band is presented in this paper. The unit cell is composed of a cross element and a ring element, both capacitively loaded with varactors, enabling reconfigurability. An equivalent circuit is developed and verified to demonstrate the dual-resonant operational theory and aid in the design of the dual-resonant unit cell. The equivalent circuit is used to demonstrate the underlying physics of dual-resonant reflectarray antennas and provides a systematic design procedure. The proposed design is evaluated using both full-wave simulations and measurements. The effects of external and mutual coupling and frequency tuning range on the loss and fractional bandwidth of the unit cell are presented. A continuous phase range of 375° with a peak and average loss of 4.78 and 3.09 dB at 10.0 GHz, respectively, is measured. The presented analysis provides guidelines for optimizing the unit cell performance required for high-efficiency beam-scanning reflectarray antennas.

A High-Power Microwave Reflectarray Antenna Based on Perforated Dielectric Substrate

A high power microwave antenna based on the reflectarray concept is designed and investigated in this paper. The reflectarray aperture is directly driven by an azimuthally symmetric mode and a directional boresight beam is realized through azimuthally introducing a phase shift of 90 to the phase shift profile of reflectarray unit cells. A sample model operating at X-band is designed to verify the validity of the proposed approach. Variable diameter air-filled holes through a host dielectric material are exploited as the phase-shifting unit cells because of the advantage of higher power handling capacity. Theoretical analysis and full-wave simulations are accomplished and results are in good agreements. A collimated beam of circular polarization with peak gain of 20.2 dB and axial ratio of 1.3 are achieved at the boresight direction for the design frequency of 10 GHz. The radiation performance of the proposed antenna as well as its compact structure makes it a potential candidate for high gain high power applications.

A Single-Layer Dual-Band Reflectarray Cell for 5G Communication Systems

A single-layer dual-band reflectarray cell is proposed in this work for future 5G systems. A reflectarray unit cell operating at 28/38 GHz is designed by adopting two pairs of miniaturized fractal patches, offering low losses (&lt;0.7 dB) and almost full-phase ranges (≅320°) at both operating frequencies. The proposed configuration allows to achieve very small interelement spacings and negligible mutual coupling effects between the two bands, thus assuring an independent phase-tuning mechanism at both desired frequency bands. The designed compact cell is successfully adopted to demonstrate reflectarrays’ abilities in achieving fixed scanned-beam and/or multibeam patterns, under the dual-band operation mode. Full-wave numerical validations, performed on the synthesized reflectarray structures, confirm the effectiveness of the designed dual-band configuration in achieving independent radiation patterns and quite good bandwidths, at the two designed frequencies. Thanks to its compactness and versatility in achieving both frequency diversity and multibeam/scanned-beam radiation patterns, the proposed unit cell is appealing for future 5G applications.

Dual resonance element for broadband reflectarray antenna

&lt;span&gt;A dual resonance reflectarray unit cell element has been proposed which evolved from a square patch element to enhance its bandwidth performance. A bend in the width of the element is used to modify its dimensions and surface currents for broadband operation. The results have been analyzed in the frequency band of 24 GHz to 28 GHz. Two different combinations of its dimensions are selected for the investigating of its various performance parameters. A maximum static phase range of 432° and 255° have been obtained with selected dimensions. The wide-band features of proposed unit cell element can be used particularly to design a broadband reflectarray antenna for future fast communication systems.&lt;/span&gt;

Design and Measurement of a 220 GHz Wideband 3-D Printed Dielectric Reflectarray

A wideband high-gain terahertz dielectric reflectarray working at 220 GHz is investigated both theoretically and experimentally. The reflectarray unit cell consists of a ground plane and a dielectric block. The reflection phase is obtained by adjusting the height of the block. Using the reflection phase computational algorithm, a dielectric reflectarray composed of 40 × 40 unit cells is designed and fabricated through three-dimensional (3-D) printed technology. Four types of 3-D printed material are measured using the THz time-domain spectroscopy system. It is found that the maximum gain and gain bandwidth of the proposed reflectarray is 31.3 dBi and 20.9%, respectively. Measured results are in reasonable agreement with simulated results. This result is an important step toward the 3-D printed THz dielectric reflectarray above 220 GHz.