Cross-polarization Performance Research Articles

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.

Gain Enhancement and Cross-Polarization Suppression of Cavity-Backed Antennas Using a Flared Ground Cavity and Iris.

Herein, we present new design principles for gain enhancement and cross-polarization suppression in dual-polarized cavity-backed antennas and demonstrate the capability in an octagonal cavity-backed open prism antenna (OCROP). In our approach, the gain is enhanced through an optimal flaring procedure and a novel metallic iris is used to control the electromagnetic fields and thereby reduce the cross-polarization. Previously, we investigated a dual-polarized OCROP antenna configuration and were able to simultaneously achieve 50% impedance bandwidth, 40% cross-polarization bandwidth (≤25 dB), and 10.2 dBi peak gain. In this study, we investigated gain enhancement by flaring an upper section of the ground cavity sidewalls, while maintaining a constant cavity height. Two cases were investigated: (1) the flare angle was modified, while the ratio of the non-flared to flared sidewall heights was kept constant, and (2) the ratio of the non-flared to flared sidewall heights was varied. In case 1, we established that, while increasing the flare angle results in a gain increase, there is a limit, as cross-polarization at the upper operating frequencies increases. In case 2, we were able to reduce the aperture phase error and achieve a higher peak gain of 12.8 dBi. To address the increased cross-polarization at the high frequency end when a large flare was used, we added a metallic iris at the junction of non-flared and flared sidewalls. We showed that increasing the iris width generally decreases the cross-polarization at high frequencies, without compromising the gain and impedance bandwidth. At an optimal width, it provides a nearly constant, low cross-polarization (below -25.8 dB) and a peak gain of 13.3 dBi, across the entire 50.7% impedance bandwidth of the antenna. We fabricated and successfully tested a prototype to verify the design and simulation approach. These results prove that incorporating an aperture flare with a metallic iris can significantly improve the gain and cross-polarization performance of cavity-backed antennas.

Wideband Dual-Polarized Octagonal Cavity-Backed Antenna with Low Cross-Polarization and High Aperture Efficiency

Simultaneously enhancing multiple antenna performance parameters is a demanding task, especially with a challenging set of design goals. In this paper, by carefully deriving a compatible set of enhancement techniques, we propose a compact/lightweight/low-cost high-performance L-band octagonal cavity-backed hybrid antenna with multiple attractive features: dual-polarization, wide impedance bandwidth, low cross-polarization, high gain, and high aperture efficiency. The ground cavity is octagonal, which allows the antenna to have a small footprint, and, more importantly, low cross-polarization and high aperture efficiencies when compared to a commonly-used square design. The hybrid design relies on the resonance merging of two radiating elements, i.e., radiating feedlines and a conductive open prism, to form a wide impedance bandwidth. To permit polarization diversity and low cross-polarization, it is differentially and orthogonally fed. Herein, a series of parametric simulation studies on antenna configurations provide information on how to improve the impedance bandwidth and cross-polarization performance. To verify the simulation studies, an antenna prototype was fabricated and tested. Excellent agreement between the simulated and measured results was reached.

Improving Compact Short Backfire Antenna Gain and Cross-Polarization Using Choke and Ring Cavity Loading

We present two designs that improve the gain and cross-polarization performance of the waveguide-fed short backfire (SBF) antenna by introducing a choke (SBF-2) and by loading the cavity with a metallic ring feature (SBF-2-Ring). A series of parametric simulation studies on antenna dimensions provides information on how to improve the antenna gain and cross-polarization performance while simultaneously extending the impedance bandwidth. For SBF-2, the peak gain was 16.6 dBi, the minimum cross-polarization ratio was −23.8 dB, and the maximum impedance bandwidth was 27.3%, with a gain bandwidth of 19.2%. For SBF-2-Ring, the peak gain was 15.8 dBi, the minimum cross-polarization ratio was −29.1 dB, and the maximum impedance bandwidth was 43.5%, with a gain bandwidth of 31.8%. The concepts were verified by designing, fabricating, and testing two prototypes in the microwave C-band. Excellent agreement between simulation and measurement was achieved. The measured gain for SBF-2-Ring was >14 dBi for 4.7–6.2 GHz and the worst case cross polarization in the diagonal plane was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -22$ </tex-math></inline-formula> dB for 5.3–5.8 GHz. Cross-polarization in the principal planes has significantly greater bandwidth and the worst case analysis is presented to give limitations on the performance.

Ultra-thin, wide-angle and bandwidth-enhanced linear and circular metasurface-based reflection-type polarization converter at X-band microwave frequency

In this study, a low-profile ultra-thin metasurface-based reflection-type polarization converter with enhanced bandwidth for X-band (8.2–12.4 GHz) applications is proposed. The designed converter, which has a cell topology above a substrate (FR-4) material terminated in a metal conductor with overall thickness of 1.2 mm corresponding to a thickness of in terms of wavelength (ultra-thin), indicates the cross polarization performance with a polarization converter ratio (PCR) value of 90% in a wide (9–12 GHz) frequency range (normal incidence) and linear to circular polarization performance with left-handed circular polarization between 8.44 and 8.58 GHz and between 12.74 and 13.14 GHz. It is observed that the converter has a PCR value of 80% for incidence angles up to . Simulations of the designed converter performed by a commercial electromagnetic simulation program (CST Microwave Studio) were validated by free-space measurements.

An injection molded circularly polarized endfire multibeam antenna with wide axial ratio beamwidth coverage using rhombic waveguide element

This article presents a circularly polarized (CP) endfire multibeam antenna with wide axial ratio (AR) beamwidth coverage. It is based on a dielectric loaded waveguide structure and consists of a 4 × 4 Butler matrix and four rhombic waveguide elements. Regarding to each element, it decomposes the incoming linearly polarized waves into two orthogonal modes with equal amplitude and obtains 90° phase difference between the two modes via their different dispersion characteristics to realize CP radiation. Study found that the proposed element has low cross-polarization performance within a wide beamwidth, which contributes to realize wide 3-dB AR beamwidth coverage in the multibeam array. In fabrication process, injection modeling and electroplating techniques are employed to construct the proposed antenna. By using this way, the structure splitting and misalignment problems, which usually existed in conventional designs, can be avoided, and the antenna weight can be maintained to a moderate level. Through the experiment, it is found that the proposed antenna can achieve an overlapped 3-dB AR bandwidth of 10.7% from 9.7 to 10.8 GHz and a wide 3-dB AR beamwidth coverage of 91°.

Computational electromagnetics for the SKA-Low prototype station AAVS2

We summarize the activities conducted since 2019 in the numerical electromagnetic analysis of one prototype station of the SKA-Low telescope. Working closely with the SKA Observatory, two teams based in Australia and Italy have collaborated effectively in modeling and analyzing AAVS2, which is the most recent prototype of an SKA-Low station installed in Western Australia. A comprehensive overview of the main electromagnetic parameters at element and array level obtained with two different commercial solvers is presented. Results for scattering parameters, individual element patterns, and station beams are shown; all these fully incorporate mutual coupling effects. Sensitivity of the station is addressed, as the cross-polarization performance. Finally, we also address some lessons learned and their impact on the project.

Wideband Reflectarrays for 5G/6G: A Survey

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.

Reduced Cross-Polarization Patch Antenna with Optimized Impedance Matching Using a Complimentary Split Ring Resonator and Slots as Defected Ground Structure

An innovative method is proposed to improve the cross-polarization performance and impedance matching of a microstrip antenna by integrating a complimentary split ring resonator and slots as a defected ground structure. An equivalent circuit model (ECM) enables the design take into consideration the mutual coupling between the antenna patch and the Defected Ground Structure. The input impedance and surface current density analysis confirms that the integration of a CSRR within a rectangular microstrip patch antenna leads to uniform comparative cross-polarization level below 40 dB in the H-plane, over an angular range of ± 50°. Introducing parallel slots, as well, leads to a reduction of spurious antenna radiation, thereby improving the impedance matching. Measurements conducted on a fabricated prototype are consistent with simulation results. The proposed antenna has a peak gain of 4.16 dB at 2.6 GHz resonating frequency, and hence is good candidate for broadband service applications.

Design of Low Cross-Polarization Tri-Reflector CATR with Standard Quadric Surfaces Working in Terahertz

In this paper, a tri-reflector compact antenna test range (CATR) consisting of a main parabolic reflector with a square aperture of 3 m in side length and two sub-reflectors of rotationally standard quadric surfaces working in terahertz is proposed. By using the equivalent paraboloid theory and cross-polarization elimination conditions and then combining with the appropriate shaped feed, the low cross-polarization and good quiet zone (QZ) performance of the system are achieved. The simulated results demonstrate that a cross-polarization isolation of &gt;37 dB and a peak-to-peak amplitude (phase) ripple of &lt;1.8 dB (13°) can be achieved on the principal cuts of the QZ at 100–500 GHz. At the same time, the QZ usage ratio of the CATR can reach 75%. The proposed tri-reflector CATR composed of standard quadric surfaces not only exhibits good quiet zone performance but also greatly reduces the manufacturing difficulty of the sub-reflectors and the construction cost of the system.

A Dielectric Dome Antenna With Reduced Profile and Wide Scanning Capability

The design and experimental validation of a wide scanning dome antenna with reduced profile is presented. The antenna is based on the combination of a planar phased array with limited scanning capabilities and a dielectric lens which allows to broaden the field of view. The angular variation of the scan loss can be almost arbitrarily designed if no constraint is imposed on the size of the dielectric lens. However, the focus of this article is on the size minimization of the dome as required for applications where the form factor is critical. Therefore, a lower boundary of the height of the dome is derived and imposed as a design constraint. The antenna is analyzed using in-house ray tracing and physical optics software tools. It is shown that, when the array is combined with the dielectric dome, a significant directivity enhancement can be achieved for wide scanning. A demonstrator of the lens is designed, manufactured and combined with an available phased array working in Ku-band. The experimental tests confirm the theoretical predictions, validating the analysis tools, and show a scanning range of 70° in all scanning planes over a 15% bandwidth. The directivity is enhanced by approximately 2 dB at the limits of the scanning range compared to the standalone illuminating array. The active element pattern is rotationally symmetric, thus, the radiation performance is almost independent on the scanning plane. Moreover, the dielectric lens allows to preserve the cross-polarization performance of the illuminating array without adding a significant contribution.

Contoured-Beam Dual-Band Dual-Linear Polarized Reflectarray Design Using a Multiobjective Multistage Optimization

This communication presents a dual-band design procedure applied to a very large contoured-beam reflectarray with improved copolar and cross-polarization performances for direct broadcast satellite (DBS) in dual-band dual-linear polarization. The reflectarray is elliptical, with the axes of 1.10 and 1.08 m, and provides coverage for South America in transmit (11.70-12.20 GHz) and receive (13.75-14.25 GHz) bands. The novel dual-band design approach is based on the use of a multiresonant unit cell with several degrees of freedom (DoFs). It is divided into several stages to facilitate convergence toward a broadband high-performance reflectarray. First, a narrowband layout is obtained at the central frequency with a phase-only synthesis. Then, using a limited number of DoFs, a copolar-only optimization is carried out in both frequency bands maximizing the copolar figure of merit. Finally, increasing the number of DoFs, cross-polarization requirements are also included in the optimization procedure. The optimized antenna complies with all copolar and cross-polarization requirements with a loss budget of at least 0.62 dB in both receive and transmit bands, outperforming earlier works in the literature while using a smaller antenna than previously proposed for this mission.

전개형 반사판 안테나의 패널 불완전 전개에 의한 편파특성 영향

In this study, we analyzed the effects of panel misalignment on the polarization performance of a deployable reflector antenna. If panel misalignment occurs in a parabola-type deployable reflector antenna, the antenna shape is distorted compared with the original parabola. The shape distortion causes the degradation of co- and/or cross-polarization performance. We investigated the difference in performance degradation for the cases of symmetric and asymmetric misalignments. The cross-polarization is small when the misalignment is symmetric, and approximately 68 dB higher for asymmetric misalignment than that in symmetric case. It was confirmed that the cross-polarization mainly arises from the asymmetry of the antenna.

3D Printed Corrugated Plate Antennas With High Aperture Efficiency and High Gain at X-Band and Ka-Band

A design criterion for a compact 3D printed high gain corrugated plate antenns that has high aperture efficiency and wide bandwidth is presented in this paper. The proposed design criterion is validated numerically and experimentally by fabricating 3D printed and Aluminium prototypes for X-band and Ka-band applications. The proposed antenna structure consists of two layers, where the electromagnetic energy (EM) is launched into a cavity that exists between both layers and the EM energy is coupled to the surface of the second layer. The second layer is the radiating structure which consists of three slots surrounded by a rectangular cavity and periodic corrugations that significantly improve the gain of the antennas. The 3D printed prototypes of the proposed antennas are fabricated and tested to validate the proposed design criterion, and their performance is compared to the Aluminium metallic counterparts. Using 3D printing technology, to fabricate the proposed antennas offer low cost and low weight alternatives to the Aluminium metallic prototypes. The measured results of the fabricated prototypes show high gain, high aperture efficiency, low side lobe level, and low cross polarization performance over a wide bandwidth.

Broadband Reflectarray With High Polarization Purity for 4K and 8K UHDTV DVB-S2

A broadband spaceborne reflectarray with high polarization purity is proposed for Ultra High Definition TV (UHDTV) broadcasting for direct-to-home (DTH) applications. The provided bandwidth would allow to offer DTH and other services, while the enhanced cross-polarization performance enables the improvement of a better signal-to-interference-plus-noise ratio. The broadband design procedure is based on a multi-resonant unit cell with several degrees of freedom (DoF) and an improved multi-frequency optimization algorithm. It is divided into several stages and sub-stages in order to facilitate convergence towards a broadband, contoured-beam, high-performance design, including the cross-polarization figure-of-merit in the procedure. A one-meter contoured-beam reflectarray working in a 20% frequency band with high polarization purity is presented as an example. The antenna is designed to fulfil the requirements of a European coverage for DTH UHDTV broadcasting in dual-linear polarization. The cross-polarization figure-of-merit greatly improves after the optimization procedure in the whole band, achieving values better than 37 dB in the coverage region, providing an excellent isolation between polarizations. This procedure can also be extended to other satellite applications in dual-circular polarization.

High-Performance Smooth-Walled Horn Antennas for THz Frequency Range: Design and Evaluation

Traditionally, corrugated conical horn antennas have been the main choice for use in astronomical receivers in the range of millimeter and submillimeter waves. They present low cross-polar level and high coupling efficiency into the fundamental Gaussian mode. However, this type of antenna is difficult to manufacture, inevitably increasing its price and extending the production process. In this article, we present two kinds of feed horn antennas, aimed for use in a frequency range equivalent to atacama large millimeter/submillimeter array (ALMA) Band 6 (211–275 GHz), which can be fabricated in a much simpler way with the conventional machining tools. Specifically, we present the design and performance comparison of smooth-walled spline-profile horns in two geometries, diagonal, and conical. Optimization of the designs has been made by means of an algorithm that allowed us to obtain models whose electrical and mechanical characteristics make them competitive when compared with corrugated horns. In particular, they are $\text{40}\%$ shorter than the conventional corrugated horns suited for this band, representing an advantage given the stringent space constraints of most astronomical receivers. We also demonstrate that they can be coupled efficiently to an astronomical-grade optical system, using ALMA Band-6 receiver as an example. Furthermore, we have constructed the diagonal horn and characterized it thoroughly. Experimental results of the radiation pattern at room temperature show a good cross-polar performance with levels below −20 dB and Gaussicity above $\text{96}\%$ . Our calculations show a good antenna-efficiency level with losses less than $\text{1}\%$ . All these properties demonstrate the feasibility of this type of horns to become the main option at the time of choosing a feed system for cutting-edge astronomical applications.

Multibeam Generation and Measurement of a DDS-Based Digital Beamforming Array Transmitter at Ka-Band

In this paper, a Ka -band digital beamforming array transmitter (DBFAT) using direct digital synthesizer (DDS) for millimeter-wave (mmW) applications is proposed. The system architecture, realization, generation, and measurement process of multiple beams are introduced. The array element consists of two kinds of tapered slot antennas with opposite fin orientations. They are placed in the side-by-side configuration such that the undesirable orthogonal electrical field is suppressed, thereby decreasing the cross-polarization level at the majority of the scanning angles. Different sets of weighting coefficients are synthesized by the DDS module, which generates various types of multibeam patterns simultaneously. Compared with the existing realized DBFAT systems, the radiation patterns of various multibeam scenarios are investigated and measured. Also, all of the mmW channels are placed on a single board, making the overall system much more compact. In addition, compared to DBFAT, which consists of identical array elements, the cross-polarization performance of the proposed DBFAT is improved within a wide range of scanning angles. As a proof-of-concept example, a 15-element linear DBFAT system prototype is fabricated and measured, confirming the validity of the presented technology, which can be utilized as a simple and low-cost alternative for evaluating the radiation performance of mmW DBFATs.

Benchmarking Ultrawideband Phased Antenna Arrays: Striving for Clearer and More Informative Reporting Practices

This article presents embedded element design and measurement data for an ultrawideband (UWB) flared-notch (Vivaldi) array. The U.S. Naval Research Laboratory (NRL) built this all-metal dual-polarized phased array specifically as a benchmarking reference for other planar phased-array apertures in the 2-21.2-GHz frequency range. It is suitable for comparative reporting of new array radiator performance, a practice favored by the Navy for effective technology readiness level (TRL) assessment. The 256-port (16 t 16, 7-mm array lattice spacing) slant-linear array is precision machined to ensure consistent agreement between measured performance results and predictions from simulated full-wave models, making the array desirable for benchmarking new array hardware as well as validating computational modeling tools. The optimally sampled aperture has excellent matching and zero scan blindness out to 80d in all scan planes, for grating-lobe-free scans over roughly 2-21.2 GHz. Benchmarking is tailored to highlight cross-polarization (cross-pol) performance in all scan planes, an important metric that should be tested during array radiator design. This data can be made available to design engineers for comparative evaluation of new UWB radiator performance under a cooperative research and development agreement (CRADA). NRL provides this and similar benchmarking data sets (and related measurement services) in the 0.8-75-GHz range.

A broadband and low cross polarization antenna with a balun of microstrip line coupling to slot line.

In this paper, a wide-band low cross polarization antenna with a structure of microstrip line coupling to slot line as the balun is proposed. The radiation part of the antenna is fed by two pairs of parallel transmission line via a transition from a slot line which is coupled by a microstrip line. Because it is fed by parallel transmission lines, which is balanced-fed structure, the antenna can achieve an improved low cross-polarization performance. The height of the antenna is 0.146λ0 (λ0 is the wavelength of lowest frequency). The prototype antenna demonstrates a measured impedance bandwidth of 93.5% (2.7–7.44 GHz), a 3-dB-gain bandwidth of 77% (2.7–6.1 GHz), and a maximum gain of 10.5 dBi at 4.5 GHz.

General Framework for the Efficient Optimization of Reflectarray Antennas for Contoured Beam Space Applications

This paper describes a general framework for the optimization of very large reflectarrays for space applications. It employs the generalized intersection approach as optimizing algorithm, integrating a number of techniques that substantially improve the baseline algorithm by accelerating computations while preserving the accuracy of the electromagnetic analysis. In particular, a learning algorithm based on support vector machines is used to obtain a surrogate model of the reflectarray unit cell accelerating the analysis more than three orders of magnitude. For the optimization, the gradient computation is accelerated by employing the technique of differential contributions on the radiated field, which avoids the use of the fast Fourier transform in the computation of the far field. Finally, to improve the cross-polarization performance, instead of optimizing the crosspolar pattern, the crosspolar discrimination or crosspolar isolation is optimized, improving both the antenna and algorithm performances. Relevant numerical examples are provided to show the capabilities of the proposed framework for a Direct Broadcast Satellite mission, showing how to design a contoured beam reflectarray with a European footprint with two different coverage zones. In addition, a complete study of computing time is carried out to analyze the impact of each technique in the optimization process.