Wide-angle Impedance Matching Layer Research Articles

On the Cross-Polarization Levels of Arrays With Wide Angle Impedance Matching Layers

On the Cross-Polarization Levels of Arrays With Wide Angle Impedance Matching Layers

A circularly polarized phased array antenna with 60° scanning in the D-plane using a top-loaded patch

The requirements for circularly polarized (CP) phased array antennas are growing with the rapid development of electronic systems. To achieve a low-profile, wideband, and large scanning-angle CP, we constructed a novel CP unit cell with a two-layer folded coupling patch and a top-loaded patch. The design of the folded coupling patch was based on the principle of reverse current cancellation. Compared with the single-layer coupling patch, the folded coupling patch suppressed the occurrence of strong in-band resonance and obtained a wider axial ratio (AR) bandwidth. To solve the problem of AR performance deterioration in the D-plane scanning, we introduced the top-loaded patch to replace the thick wide-angle impedance matching layer, which improved the difference in co-polarization components and reduced cross-polarization level. Thus, a large scanning angle of more than 60° in the D-plane was obtained. An 8 × 8 planar array based on the proposed CP unit cell was designed. The array achieved a 3.9:1 (3.2–12.5 GHz) AR bandwidth and up to 60° scanning angle in the D-plane and 70° in the E-/H-plane; an AR smaller than 3 dB was demonstrated over the entire scanning range.

A Monopole-Based Wideband Absorber for Ultralarge Angles

This article develops a broadband absorber by fully using the radiation features of monopole antennas for ultrawide-angle absorption application. A unit cell (UC) based on monopole antennas is proposed, and its working polarization is analyzed with the antenna reciprocity method and image theory. A wide-angle impedance matching layer is also introduced to further enhance the absorption at large angles. The optimized monopole-based UC reveals 90% absorptivity from 5.5–14.76 GHz at the incident angle of 80°. To the best of our knowledge, this is the first time to report an absorber that can work perfectly under such ultrawide angles in a broadband manner. An 11 × 36 array is configured and simulated to verify the effectiveness of the monopole-based UC. The monostatic and bistatic scattering are both reduced significantly as well as other diffuse scattering directions from the simulated results. A prototype of 110 mm × 360 mm is fabricated and measured. Time gating methods are adopted to diminish the direct coupling effect. The measurements are in good agreement with the full-wave simulation results.

Methodology for Improving Scanning Performance Loading an Array Element with a 3D All-Metal WAIM

All-metal 3D printing technologies are allowing the conception of new structures for different applications. This publication explores the potential of employing for the first time an all-metal 3D unit-cell topology to perform wide-angle impedance matching layers. A new equivalent circuit is derived for the oblique incidence, providing a good estimation of the cell response for the scanning range (θ=[0°,55°]) in the main scanning planes for a linearly polarized radiated field. This analytical model is later used to develop a wide-angle impedance matching design methodology for a generic antenna. This methodology is tested in practice to match a phased array made of metallic horns at 18 GHz. An improvement of 5 dB is obtained in the simulations for angles θ>35° for the H-plane.

Design of an S-Band Phased Array with Modified Dipoles

A wideband, low cross-polarization, high-gain, and wide-angle scanning antenna array is presented in this paper. The antenna array contains 8 subarrays in the horizontal dimension, and each subarray contains 4 unit cells. A two-side printed dipole with an amendatory equivalent circuit model is adopted, and the metal vias are introduced in the element design to ameliorate the cross-polarization level. A radome, acting as the wide-angle impedance matching layer, is introduced to achieve wide-angle scanning. A prototype of a 4 × 8 array is fabricated and measured. The results show that the operating bandwidth of aperture efficiency (BWAE) above 60% is about 26.7% from 2.6 GHz to 3.4 GHz. The measured scanning loss in the H-plane is 2.7 dB when scanning up to 60° with active voltage standing wave ratio (VSWR) <3, and the gain can achieve 21 dB at 3 GHz with a cross-polarization level below −30 dB at all angles.

Conjugate Impedance Matching Method for Wideband and Wide-Angle Impedance Matching Layer With 70° Scanning in the H-Plane

This letter proposes a wideband and wide-angle conjugate impedance matching (WWCIM) method and a WWCIM layer, which are applied to the tightly coupled dipole array (TCDA). The impedance matching problem over an ultrawideband can be well solved by using this method when the scanning angle reaches 70° in the H-plane. At the port position, the impedances of the ultrawideband-phased array change sharply at different frequencies when scanning to large angles in the H-plane. However, we find that the impedances at the upper surface of the array have certain regularity when scanning in the H-plane. The impedances gradually decrease as the scanning angle increases in the H-plane and the reactance parts of the impedances are inductive. Therefore, a new WWCIM layer is proposed. The impedances of the WWCIM layer, seen from down to up, also gradually decrease as the scanning angle increases in the H-plane. But their reactance parts are capacitive. Therefore, in the H-plane, the impedances at the upper surface of the TCDA and the impedances at the lower surface of the WWCIM layer can be well conjugated when scanning to large angles. In the E-plane, because the changes of the port impedances and the WWCIM layer are small within the 70° scanning range, the port impedances can be easily matched. Thus, the impedance matching problem is well solved when scanning at large scanning angles in the H-plane. Finally, a single-polarization array with a bandwidth of 1.02–5.15 GHz (VSWRs λ at the lowest working frequency.

Efficiency improvement and cross-polarization reduction of single-fed frequency-scan leaky wave microstrip antennas by using an M-shape metasurface as the WAIM layer

Increasing the efficiency and reducing the cross polarization of a single-fed leaky wave antenna by using a wide-angle impedance matching (WAIM) layer are studied in this paper. A wideband serial-fed patch array on a two layer substrate is employed as the leaky wave array. Dimensions of the patch array are optimized for the lowest reflection coefficient between 6 GHz and 7 GHz. The proposed antenna is indeed a frequency-scan antenna in this frequency range. Miniaturization of the proposed leaky wave microstrip antenna is achieved by using circular lines instead of straight lines between the patches. Reducing the separations between the array elements (microstrip patches) led to the sidelobe level reduction of the radiation patterns. Further improvements on the antenna results are obtained by using an anisotropic metasurface WAIM layer. The proposed metasurface layer is composed of printed M-shape unit-cells on a thin substrate, leading to the gain enhancement, sidelobe level reduction, cross-polarization reduction and reflection coefficient reduction of the antenna. Finally, the predicted results are validated by using experimental results, indicating good agreements. As a result, the performance improvement of the antenna by using the WAIM layer is observed in the simulations and measurements, clearly.

Ultra-Wideband and Wide-Angle Microwave Metamaterial Absorber

In order to extend the performance of radar absorbing materials, it is necessary to design new structures with wideband properties and large angles of incidence which are also as thin as possible. The objective of this work, realized within the framework of the SAFAS project (self-complementary surface with low signature) is, then, the development of an ultra-wideband microwave absorber of low thickness. The design of such material requires a multilayered structure composed with dielectric layers, metasurfaces, and wide-angle impedance matching layers. This solution has been realized with on-the-shelf materials, and measured to validate the concept. At normal incidence, the bandwidth ratio, defined for a magnitude of the reflection coefficient below −10 dB, is 4.7:1 for an absorber with a total thickness of 11.5 mm, which corresponds to λ/7 at the lowest operating frequency. For an incidence of 60°, this bandwidth ratio is reduced to 3.8:1, but the device remains ultra-wideband.

Wideband Dual-Polarized Linear Array of Tightly Coupled Elements

Previous studies on tightly coupled dipole arrays (TCDAs) are mainly focused on 2-D phased arrays, where very wide bandwidth can be achieved as compared to 1-D TCDAs. Moreover, for the dual-polarized case, the interelement coupling is not sufficient in the polarization along the transverse direction of linear array, which leads to a much narrower bandwidth. In this communication, a wideband dual-polarized tightly coupled dipole linear array (TCDLA) is proposed. A novel vertical parasitic superstrate layer is employed in the dual-polarized linear array to compensate the impedance variation in beam scanning cases. As compared to traditional wide-angle impedance matching layer composed of layered dielectric sheets, the vertical parasitic superstrate layer greatly reduces the weight of the array. Simulation results show that the TCDLA achieves 5:1 bandwidth and 4:1 bandwidth in the vertical polarization and horizontal polarization, respectively, for VSWR $1 \times 26$ linear array is fabricated and measured. Good agreement is achieved between measured and simulation results.

Multiscale System-by-Design Synthesis of Printed WAIMs for Waveguide Array Enhancement

A task-oriented multiscale material synthesis problem is addressed through an instance of the system-by-design (SbD) paradigm. More specifically, wide-angle impedance matching (WAIM) layers based on printed metasurfaces are designed to enhance the radiation efficiency of planar phased arrays. Toward this end, a task-oriented formulation is adopted where the layer geometrical features are the microscale solution descriptors, while the minimization of the array power reflection is the synthesis macroscale objective. The WAIM synthesis (i.e., the definition of the microscale structure of the WAIM and not the dielectric properties of the WAIM layer, unlike previous approaches) is yielded through an iterative process in which the direct optimization of its unit cells is made possible by the SbD mapping between the WAIM microscale features and the associated macroscopic properties. Selected numerical examples are presented and discussed to illustrate the current potentialities in terms of performance, feasibility, and computational efficiency of the proposed design strategy also in comparison with recent and competitive state-of-the-art WAIM design methodologies.

Floquet Modal Based Analysis of Overlapped and Interlaced Subarrays

A methodology is presented to analyze overlapped and interlaced (interleaved) subarrays. The analysis is based on eigen vector excitation coupled with Floquet modal expansion of the subarray fields. Numerical results of interlaced and overlapped subarrays using probe-fed patch elements are presented. It is found that for wide angle scan overlapped subarrays have superior performances over interlaced and conventional subarrays with and without wide angle impedance matching layer.

Wide angle impedance matching metamaterials for waveguide-fed phased-array antennas

This work investigates the gains realisable through the use of artificially structured materials, otherwise known as metamaterials, in the wide angle impedance matching (WAIM) of waveguide-fed phased-array antennas. The authors propose that the anisotropic properties of a metamaterial layer, when designed appropriately, can be employed to achieve impedance matching at a wide contiguous range of phased-array antenna transmission angles. Simulation and numerical results show that an optimised impedance match over a broad angular range can be readily achieved using a doubly uniaxial (magnetic and electric) anisotropic layer, an outcome not found accomplishable when an optimised isotropic dielectric layer is used. The authors propose the possibility of using metamaterials to achieve anisotropic WAIM layer configurations, and the authors show, using two simple uniaxial designs, that a metamaterial layer over the phased-array gives performance characteristics similar to its homogeneous anisotropic effective medium counterpart.