Wide-angle Impedance Matching 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.

Low-Profile Planar Ultrawideband Modular Antenna Array Loaded With Parasitic Metal Strips

A low-profile dual-polarized planar ultrawideband modular antenna (PUMA) array is proposed in this paper. The overall profile is as small as 11.4 mm (0.228λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> is the free-space wavelength at the highest operating frequency) based on element sizes 25 × 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.5 × 0.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and a large operating frequency bandwidth achieved by loading lossless parasitic metal strips between the dipole patch and the ground plane. The loop-mode resonance that causes deterioration of the port isolation around the lowest operating frequency is comprehensively analyzed and suppression methods are proposed. To further reduce the overall profile, a metasurface-based wide-angle impedance matching (MS-WAIM) layer is introduced. The surface waves guided by the MS-WAIM layer during wide-angle scanning in H-plane are suppressed by cutting properly-sized square holes at critical positions. The calculated results show that the proposed infinite array can scan up to ±60° in E/H-planes with active VSWRs below 2.9 within 2–6 GHz and orthogonal port isolations beyond 20 dB. A 12 × 11 array prototype is fabricated and reasonable agreement is achieved between the calculated and measured results.

A Low-Profile Ultra-Wideband and Wide-Scanning Phased Array for UHF Applications

This article presents a novel low-profile ultra-wideband and wide-scanning array antenna using the transversely connected folded tightly coupled dipoles array (TCF-TCDA). The tightly coupled folded dipole arms are used to extend the operational frequency band with a simple feed structure. The capacitively-loaded metallic walls are adopted to move the problematic common-mode resonance out of the desired band and mitigate the bandwidth-limiting loop mode at the lower frequency, as well as reducing the weight and cost. A meta-surface-based wide angle impedance matching (MS-WAIM) layer is used to improve the beam scanning ability and lower the antenna profile, which consists of the star-shaped patches loaded on the dipole element. To demonstrate the wideband and wide scanning-range capability, a prototype is designed with an 8:1 bandwidth (0.41–3.3 GHz) at broadside, a scanning range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \mathrm{75}^{\circ }$ </tex-math></inline-formula> from 0.5 to 3.25 GHz (6.5:1 bandwidth) in the E- and D-planes and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \mathrm{50}^{\circ }$ </tex-math></inline-formula> from 0.6 to 3.3 GHz (5.5:1 bandwidth) in the H-plane for active VSWR < 3.6. The proposed antenna has a very low profile, which is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.07\lambda _{\mathrm {low}}$ </tex-math></inline-formula> at the lowest operating frequency. A 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 16 array prototype is fabricated and measured. Experimental results show that the design and measurement results have good agreement. The proposed antenna has an ultra-wide bandwidth, a wide scanning range, a very compact size and a low cost, which is a good candidate for modern wireless system.

Design of a Dual-Polarization All-Metal Vivaldi Array Antenna Using a Metal 3D Printing Method for High-Power Jamming Systems

This paper proposes an all-metal Vivaldi array antenna with a wide-angle impedance matching (WAIM) layer for high-power jamming systems. To reduce fabrication complexity and time, the proposed array antenna is manufactured using a metal 3D printing method. The Vivaldi unit cell, composed of a radiating flare part and an inner cavity, is extended into an 8 × 8 array with a ±45° slant configuration. To further enhance the beam steering angle, the WAIM layer is placed on top of the proposed array antenna. The performances of the proposed array antenna, such as its active reflection coefficients (ARC), gains, and array radiation patterns, are investigated in a full anechoic chamber. At a steering angle of (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 45°, ϕ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 25°), the measured and simulated average ARCs of the center element (Port 36) with the WAIM layer are –13.2 dB and –18.5 dB, respectively. At 4 GHz, the measured and simulated bore-sight gains of the proposed array antenna are 19 dBi and 20.6 dBi, respectively. In addition, the measured and simulated bore-sight gains for the (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 45°, ϕ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 0°) steering angle in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">zx</i> -plane are 18 dBi and 21 dBi, respectively. In the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">zy</i> -plane, bore-sight gains for the (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 45°, ϕ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 0°) steering angle are 19.3 dBi by measurement and 19.1 dBi by simulation. These results demonstrate that the proposed array antenna is suitable for high-power jamming systems because stable bore-sight gains are observed even at wide steering angles without unwanted grating lobes.

Ultra-wideband dual-polarized tightly coupled dipole array with double layers meta-WAIM

An ultra-wideband dual-polarized tightly coupled dipole array (TCDA) with 10:1 bandwidth is presented. Aimed at solving the ultra-wideband impedance matching problem between the antenna and free space, a novel meta-material wide-angle impedance matching (WAIM) layer is presented. The meta-WAIM utilized a structure of planar double layers with the elliptical split ring on top and the concentric split ring on the bottom, which improves the beam scanning ability over the high-frequency band. The dual-polarized dipoles are arranged as “egg-create” and fed by the integrated double-Y balun. A resistive frequency selective surface (FSS) is loaded between the dipole and ground plane to improve the active VSWR and lower the overall profile, simultaneously. The proposed antenna array can operate over a 10:1 bandwidth (0.2–2 GHz) with an active VSWR < {2.1, 2.7, 4} and average radiation efficiency > {71.6 %, 68.9 %, 60.3 %} for the scan up to {broadside, 45°, 60°}, respectively. The overall antenna profile is 95 mm, which is only 0.063λL evaluated at the lowest operating frequency. A prototype of a 6 × 10 array is simulated, fabricated, and measured. Good agreement is achieved between the simulated and measured results.

An Ultra-wideband, Low-profile tightly coupled array with inductive windows and split rings

A band-enhanced and low-profile tightly coupled array (TCA) with inductive windows (IWs) and split rings (SRs) is proposed in this paper. The IW cell is placed between the antenna plane and ground and consists of four parallel strips which introduces inductance to move the resonance frequency caused by the ground out of the operating band. Moreover, the SR is specially designed to thin the thick wide-angle impedance matching (WAIM) superstrates to reduce the TCA profile height. As a result, the proposed array has a 10:1 impedance bandwidth (0.6-6 GHz) with the active VSWR<3.0 and more than 90% radiation efficiency at broadside. The bandwidth reduces to 8.8:1 (0.7-6.2 GHz) when scanning to ±60° in E/D-plane and ±45° in H-plane, respectively. The profile height of the TCA with IWs and SRs is only 0.077λL with the distance of 0.5λH between the adjacent elements.

Hydroacoustic High Absorption with Broadband and Wide-Angle Impedance Matching

We numerically demonstrate a general method to achieve acoustic high absorption in water with a wide range of incident angles and a broad frequency bandwidth. Different from previous studies considering local resonances with a narrow bandwidth or porous materials with a gradient design, we show that flat multilayer solid composites can be engineered to be perfectly impedance matched with water over a wide range of angles and a broad spectrum. By adding a proper loss factor to the composites, sound waves can be gradually dissipated and high absorption can be realized. Such a method is robust and adaptive to a broad range of material parameters. Our work could promise broad underwater applications.

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&gt;35° for the H-plane.

Wide-Angle, Ultra-Wideband, Polarization-Independent Circuit Analog Absorbers

In the analysis of most circuit analog (CA) absorbers, it is only the absorption performance under normal incidence that is taken seriously, leading to a much worse absorption with the increase of incident angle, especially when it is larger than 30°. In this communication, a novel absorber, which consists of a conductive square-loop (SL) array embedded with lumped resistors and a well-designed wide-angle impedance matching (WAIM) layer, is proposed. Equivalent circuit (EC) and strict formula derivations are introduced to present a great insight into the deterioration of absorption performance under oblique incidence and the effect of WAIM layer. An absorber sample is further fabricated and measured for verification. It is shown through measurement that the structure has a fractional bandwidth of 137.1% for at least 10 dB reflection reduction under normal incidence. When the incidence angle is increased to 45°, the overlapped bandwidth for both transverse electrical (TE) and transverse magnetic (TM) polarizations is still measured to be 110.5%.

Substrate-Integrated Cavity-Backed Array With Controlled Mutual Coupling for Wide Scanning

In this letter, a planar triangular-lattice array with suppressed mutual coupling (MC) is proposed for wide scanning. The array element is comprised of two interconnected substrate-integrated cavities (SICs) with identical slots. An embedded feeding network is used to excite equal-amplitude and in-phase radiations of the two SIC-backed slots, yielding nearly cosine-type isolated element patterns that cater for the wide scanning. With the cancelation of common-mode couplings and the low-coupling characteristic of the differential mode, the phased array exhibits suppressed MC. Wave-trap resonators are loaded for the further reduction of MC, resulting in the wide-angle impedance matching. The array offers wide-angle beam steering up to ± 65° in E-plane, ± 50° in H-plane, and ± 60° in D-plane, with mitigated fluctuation of realized gain.

A Ferrite-Loaded Ultralow Profile Ultrawideband Tightly Coupled Dipole Array

A dual-polarized ferrite-loaded ultrawideband tightly coupled dipole array (TCDA) with an extremely low profile is presented. A novel ferrite grid with high relative permeability and permittivity characteristic is loaded between the antenna and the ground plane, which expands the low-end of operation bandwidth and reduces the overall profile, simultaneously. An X-shaped frequency selective surface (FSS) is utilized as a special band-stop filter to improve the realized gain at higher frequencies. Meanwhile, the proposed array utilizes a microstrip (MS) to coplanar stripline (CPS) uniplanar double-Y balun to achieve unbalance&#x2013;balance transformation and impedance matching. A thin meta-surface-based wide-angle impedance matching (MS-WAIM) layer is introduced to improve the beam-scanning ability. Simulated results show that the proposed antenna is able to operate over a 10:1 bandwidth (0.2&#x2013;2 GHz) with active VSWR &#x003C; &#x0007B;2, 2.6, 3.4&#x0007D; while scanning up to &#x0007B;broadside, 45&#x00B0;, 60&#x00B0;&#x0007D;, respectively. Most of all, the overall antenna profile is only 62.5 mm (<inline-formula> <tex-math notation="LaTeX">$0.042\lambda _{\mathrm {L}}$ </tex-math></inline-formula>) at the lowest operating frequency, which is known to be the thinnest 10:1 ultrawideband array with wide angle scanning (&#x00B1;60&#x00B0; in E- and H-plane) performance. A prototype of <inline-formula> <tex-math notation="LaTeX">$6 \times 8$ </tex-math></inline-formula> array is simulated, fabricated, and measured. Good agreement is achieved between the simulated and measured results.

A Low-Profile and Wide-Angle Scanning Planar Ultrawideband Modular Antenna With Ultra-Thin Loading Window

Ultrawideband phased antenna array has been widely used in communications, radars and detection. However, the high profile and poor wide-angle scanning characteristics have always been the critical limitation for many available ultrawideband antenna applications. In this paper, an ultra-thin loading window (UTLW) is proposed to replace the wide-angle impedance matching (WAIM) superstrate in the planar ultrawideband modular antenna arrays (PUMA), and reduces the profile height greatly. The UTLW consists of two strips in parallel, and each strip is loaded with two resistors and one capacitor. Following the equivalent circuit model (ECM) of the PUMA, the resistance and capacitance are specially designed to make the complex impedance of the UTLW equal to the impedance introduced by the WAIM. A dual-polarized PUMA with an UTLW achieves 6-18 GHz impedance bandwidth with active VSWR≤2.6 for scanning up to 60° and active VSWR≤3 for scanning up to 70° in E/D/H plane. The profile height of the proposed PUMA is only less than 0.07λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>l</i></sub> , or, 0.24λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>h</i></sub> with reference to the typical Nyquist half-wavelength spacing frequency. A 20×20 prototype PUMA with the UTLW was fabricated and its measured results were found consistent with the simulation results.

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) &lt;3, and the gain can achieve 21 dB at 3 GHz with a cross-polarization level below −30 dB at all angles.

Fully integrated wideband phased array with large scan range and 5:1 bandwidth

In this work, a fully integrated phased array using multi-layer printed circuit board (PCB) fabrication technologies is presented. This array is directly fed by 50 Ω coaxial cables, without balanced-to-unbalanced transitions. An asymmetric dipole is used to achieve stable input impedance. Furthermore, to broaden the operating bandwidth, a coupling patch is designed beneath the asymmetric dipole , which also eliminates the common-mode resonance and decreases the array profile. In addition, three wide-angle impedance matching (WAIM) layers with different structures are utilised to improve the scan range in all scanning planes. Infinite array simulations indicate that the proposed array can operate over a 5.1:1 bandwidth (2.4 ∼ 12.2 GHz) with an active voltage standing wave ratio below 3 while scanning up to ± 60° in H plane and ±75° in the E plane. Furthermore, the proposed antenna, whose cross-polarization levels remain below −35 and −7.5 dB when scanning up to 75° in the E plane and 60° in the D plane, demonstrates the merits of high polarization purity. Array simulations are verified by the measurements of a 12 × 12 prototype, and good agreement is observed.

Design of an Active Beam-Steering Array With a Perforated Wide-Angle Impedance Matching Layer

In this communication, a tapered slot antenna array with a perforated wide-angle impedance matching (WAIM) layer is studied for active beam steering. To achieve the wide-angle beam scanning characteristic, a tapered slot antenna is used in the array antenna design. For active impedance matching in a wide beam-steering angle, a thin dielectric type of WAIM is introduced, and an optimal WAIM characteristic is realized by changing the effective dielectric constant by adding an air hole to the WAIM. To verify the characteristics of the designed antenna, a 16×16 array is fabricated and measured. The fabricated array shows active S-parameter characteristics of less than -9.13 dB during E-plane scanning and -9.31 dB during H-plane scanning when the beam is steered up to 70° on both planes. It was also confirmed that when the beam is steered to 70°, no scan blindness or grating lobes occur within the operating frequency.

A Wideband and Wide Scanning Tightly Coupled Dipole Array with Meta-Surface Wide-Angle Impedance Matching

A low profile ultra-wideband tightly coupled dipole array is studied. The antenna elements are fed by Marchand baluns of small size and low cost. A metasurface based wide-angle impedance matching (MSWAIM) layer is introduced to replace the traditional dielectric WAIM, improving the beam scan performance and reducing the antenna profile. The simulation shows that the proposed antenna array can operate over 2.4-12.4 GHz, approximately 5:1 bandwidth with maximum scanning angle of 50o for both E plane and 45o for H plane. The antenna profile above the ground is only 0.578λH at the highest operating frequency. This antenna array can find its application in the forthcoming massive MIMO beamforming systems for 5G.

Wide-angle, Ultra-wideband, and Polarization-insensitive Circuit Analog Absorbers

Most previous circuit analog absorbers only considered absorption performance under normal incidences, leading to bad absorption for large incident angles, particularly those > 30°. With the advancement in modern bistatic radar detection technology, radar electromagnetic waves may come from different spatial directions, thereby necessitating radar absorbers with high absorption performance under normal and oblique incidences. Thus, in this paper, we present a novel wideband absorber comprising a conductive square-loop array embedded with lumped resistors and a well-designed Wide-Angle Impedance Matching (WAIM) layer. Results show that the WAIM layer can significantly improve absorption under oblique incidences. To make the absorber design clear and simple, an Equivalent Circuit (EC) and strict calculating formulas are proposed under normal and oblique incidences. Fractional bandwidth is increased into 137.1% through measurement under normal incidence, and the structure has a common fractional bandwidth of at least 110.5% for at least 10 dB reflection reduction when the incidence angle < 45°. The similarity among EC calculated, simulated, and measured results proves the validity of the designed absorber.

Scan Blindness Free Design of Wideband Wide-Scanning Open-Ended Waveguide Phased Array

A wideband wide-scanning open-ended rectangular waveguide phased array in a triangular lattice is presented. Dielectric or metamaterial wide-angle impedance matching superstrates have been widely used in phased arrays to improve the scanning performance. However these dielectric-containing covers cannot solve the problem of scan blindness caused by the surface waves, or even further aggravate the surface wave effect. The modulated surface structures, which consist of the impedance-gradient structures and the surface wave bandgap structures are designed to maximize the wideband wide-scanning performance of the array. The proposed array achieves 40% bandwidth (8–12 GHz), while covering a scanning range of ±65° in the E-plane (VSWR < 2.3) and H-plane (VSWR < 2). The practical working frequency band occupies the whole potential operating frequency band between the waveguide TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> cutoff frequency and the onset frequency of the first grating lobe. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11\times11$ </tex-math></inline-formula> prototype is fabricated and measured. Good agreement is achieved between the simulated and measured results.