Radar Cross Section Reduction Of Antenna Research Articles

Ultra-thin wideband frequency tunable metamaterial absorber and its application for antenna radar cross section reduction

A metamaterial absorber (MMA) with broadband and efficient absorption performance based on ultra-thin dielectric layer is proposed. In this unique configuration, the absorption frequency of the MMA can be continuously and dynamically tuned across a wide frequency range by manipulating the reverse voltage of the central varactor diode. From both the equivalent circuit and field distribution perspectives, we analyze the mechanisms behind broadband tuning and superior absorption. Simulation and experimental results demonstrate that the absorption peak of MMA can be continuously tuned over a range of 5.16–8.16 GHz, with the absorption rate consistently exceeding 90%, and the thickness is only 0.5 mm. Integrating MMA array with a microstrip patch antenna in a suitable manner can dynamically mitigates the radar cross section (RCS) within the associated frequency range, with virtually negligible impact on the antenna’s radiation performance.

In-band dual-polarization RCS reduction of waveguide slot array antenna integrated with AMC and PEC chessboard structure

An in-band low radar cross section (RCS) waveguide slot array antenna (WSAA) is proposed by using a chessboard structure composed of artificial magnetic conductor (AMC) and perfect electric conductor (PEC), which serves as the antenna radiator. The method for RCS reduction is the reflection energy cancellation. Standing wave array is used to achieve higher energy efficiency and more compact antenna structure. Experimental results show that the in-band monostatic RCS is sufficiently reduced with the chessboard structure application for both co- and cross-polarized incident waves, where 10-dB RCS compression is realized among the frequency range of 9.7–9.91 GHz for co-polarization and 9.5–9.85 GHz for cross-polarization with maximum RCS reductions of −13.3 dB and −11.9 dB, respectively. Meanwhile, the designed WSAA maintains the high gain characteristics of the original WSAA. The paper provides a simple, practical and effective strategy for stable RCS compression in the operation band of waveguide antenna array, which has potential applications in stealth platforms.

Broadband Metamaterial Surface for Antenna RCS Reduction and Gain Enhancement

This paper presents a broadband metamaterial surface with low radar cross section (RCS) and introduces its application on antenna. The metamaterial surface is composed of polarization-dependent artificial magnetic conductors (PDAMCs), which are orthogonal arranged in chessboard-like configuration for backscatter cancellation. By optimizing the PDAMC cell, effective phase difference is obtained in wideband and the surface achieves 10dB RCS reduction over the bandwidth of 32%. As a potential application, the metamaterial surface is employed to replace the metallic ground of a slot antenna. Illustrated by detecting wave, the novel antenna shows low RCS at boresight. While the antenna operates, the gain gets enhanced as a result of parasitic radiation of the surface. Full wave simulations and measurements validate that the novel antenna achieves both broadband low RCS and high gain compared with the slot antenna installed on a same-size metallic plate.

Ultrabroadband RCS Reduction and Gain Enhancement of Patch Antennas by Phase Gradient Metasurfaces

In this letter, a novel design based on phase gradient metasurfaces (PGMs) is proposed to reduce the radar cross section (RCS) and enhance the gain of patch antennas. The PGM unit consists of a cross-dipole and three square-dipole rings. The proposed antenna is composed of a conventional patch radiator and four surrounding sequential-rotated PGMs. On the one hand, an ultrabroadband RCS reduction is achieved due to the PGMs phase discontinuity deflects the signal away from the specular direction by the PGMs. On the other hand, a gain enhancement is achieved because the enlarged equivalent radiation aperture owing to the coupling effect between the PGMs and the patch. A prototype operating at Ku band is designed, fabricated, and measured. It is demonstrated that an over 6 dB RCS reduction is obtained from 9.31 to 28.22 GHz, and an average 1.5 dB gain enhancement is obtained within the working band of 14.2–15.5 GHz, which can be used in stealth platforms.

Mutual coupling and RCS reduction of MIMO dielectric resonator antenna for S-band applications

This paper designs and analyses a two-port dielectric resonator-based multiple-input, multiple-output (MIMO) antenna. A tilted L-shaped aperture is used to excite the cylindrical-shaped ceramic. This type of feeding structure produces the circularly polarized (CP) waves and HEM11δ mode inside the ceramic. The proposed antenna shows two main features: (i) the polarization diversity concept reduces the isolation level by 15 dB; (ii) integration of frequency-selective surface (FSS) reduces the radar cross-section (RCS) value by an amount of 7.5 dBsm within the operating band. The fabricated structure confirms the working band of the proposed antenna from 2.8 to 3.2 GHz. 3-dB axial ratios is achieved between 2.8 and 3.05 GHz. The proposed antenna's good diversity parameter value and stable radiation characteristics make it applicable for S-band wireless applications

Wideband RCS Reduction of Slot Array Antenna Utilizing 3-D Absorptive Frequency-Selective Structure

A low radar cross-section (RCS) slot array antenna based on absorptive frequency-selective structure (AFSS) is presented in this letter. The AFSS unit cell is constructed by two lossy layers and four double-sided parallel strip lines (DSPSLs). The radiation performance of the antenna can be preserved due to the transmission window of the lossy layers. Wide absorption bands of the AFSS are achieved due to periodic impedance of the DSPSL and the combination of the lossy layers. The operating principle of the design is demonstrated, and a prototype is fabricated and measured to validate the design. The proposed design features both wide RCS reduction band of the antenna and wide transmission band of the AFSS.

Switchable Polarization-Insensitive Frequency-Selective Surface Reflector/Absorber With Low Profile by Using Magnetic Material

A multifunctional frequency-selective surface reflector (FSSR) is found to be an applicable candidate for the realization of an antenna's radar cross-section reduction in or out of its operating frequency. In this letter, a polarization-selectable in-band switchable FSSR/absorber based on diodes is designed and experimentally demonstrated, which comprises a layer of active frequency-selective surface and a layer of metal-backed frequency-dispersive magnetic material (FDMM). The design realizes the switching functions of broadband absorption band from 3.5 to 12.0 GHz (110% bandwidth) with at least −10 dB reflectivity and a reflection band at 6.2 GHz with two-sided absorption bands (2.2–4.8 GHz, 74.3% bandwidth for the lower absorption band and 7.1–12.9 GHz, 58% bandwidth for the upper absorption band) by manipulating the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> states of PIN diodes. Besides, due to the use of FDMM, the thickness of the FSSR is only 0.074 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> , making it easy to design the reflective surface of the antenna. A prototype of the proposed FSSR/absorber is fabricated and measured, where reasonable agreement is observed.

RCS reduction of microstrip antenna using split square loop thin absorber

This study proposes an electrically thin frequency-selective surface-based microwave absorber without using resistive surface and lumped resistors to make it simple and inexpensive. The ground plane of the microstrip antenna (MSA) serves as the metallic back of the absorber. The top two layers of the proposed absorber are printed on both sides of the top FR4 sheet in a square annular ring form to encircle the square patch. Both simulations and measurements are carried out to obtain the scattering parameters, which are used to retrieve the absorption coefficient, relative permittivity (ɛ r), and relative permeability (μ r). An equivalent circuit model for the proposed absorber is constructed and validated. The absorption performance is insensitive to the angle of incidence (θ) up to 50°. The absorption mechanisms are studied based on the surface current distribution, electric field distribution, and constitutive parameters. The absorber is then integrated with an MSA operating at 4.2 GHz, which gives a maximum monostatic radar cross-section (RCS) reduction of 15 dB. Numerical and experimental results of the radiation performance and the RCS of the absorber integrated antenna structure have been presented. A very good agreement between simulation and measurement results is observed.

Epsilon near zero metasurface for ultrawideband antenna gain enhancement and radar cross section reduction

A non-resonant metamaterial unit cell is proposed to design a metasurface for ultrawideband (UWB) gain enhancement and radar cross section (RCS) reduction of an UWB antenna. Epsilon near zero (ENZ) property and negative refractive index of metamaterial is achieved to ensure low loss and amplification of electromagnetic waves (EM) passing through it. The proposed metamaterial is designed on a 6 mm × 6 mm FR4 substrate with dielectric constant 4.4, height 1.6 mm and loss tangent 0.01. The unit cell is simulated with periodic boundary condition to get the properties of periodically arranged unit cells in one plane called metasurface. A Metasurface is designed by planar arrangement of 5×5 unit cells of proposed metamaterial unit cell and is kept at height of 2 mm above an ultrawideband planar microstrip antenna. Antenna system with metasurface has physical and electrical dimensions of 32 × 32 × 5.2 mm3 and 0.34λ0×0.34λ0×0.05λ0 respectively, where λ0 is the free-space wavelength at 3.2 GHz. The bandwidth of UWB patch antenna (3.1–10.6 GHz) is unaffected by the presence of metasurface. The analysis of radiation mechanism shows the phase difference of EM waves passing through metasurface with and without reflection is 300°–400°. This indicates emergence of coherent waves from metasurface and contributes in gain enhancement. Maximum gain is 5.7 dB at 6.8 GHz with radiation efficiency of 88.5% and maximum gain enhancement is 10.1 dB at 9.8 GHz. The reflection phase analysis of normal incident wave predicts the frequency for maximum RCS reduction as 6.4 GHz. Maximum RCS reduction of antenna with application of metasurface is 21 dB at 6.7 GHz. Significant gain enhancement and reduction of RCS is achieved for ultrawideband. The proposed antenna system metasurface with enhanced gain and reduced RCS is a good candidate for application in stealth and military platforms.

Transmission–Reflection-Selective Metasurface and Its Application to RCS Reduction of High-Gain Reflector Antenna

In this article, a novel transmission–reflection-selective metasurface (MS) is introduced to realize symmetric transmission for horizontal-polarized ( $x$ -polarized) waves but asymmetric reflections for vertical-polarized ( $y$ -polarized) waves propagating along opposite directions. Based on the theoretical analysis, the proposed MS is finally engineered to transmit $x$ -polarized wave but anomalously reflect $y$ -polarized wave for forward direction. As for backward direction, the designed MS acts as a polarizer grating capable of transmitting $x$ - but specularly reflecting $y$ -polarized wave. As an example of its practical application, the designed MS is applied to form a folded reflector antenna with a reduced backward radar cross section (RCS). Both the MS and the folded reflector antenna are numerically simulated, physically implemented, and experimentally measured. The measured results of the folded reflector antenna coincide well with the simulated ones, showing a peak gain of 23.1 dB and a 3 dB gain bandwidth of 29.3% (12.8–17.2 GHz), as well as a −20 dB cross-polarized level bandwidth of 41.6% (11.4–17.4 GHz). Furthermore, the backward RCS of the antenna can be reduced from 11.2 to 18.4 GHz (48.6%) for $y$ -polarization and 14.1 to 16.2 GHz (13.9%) for $x$ -polarization, with the bandwidth defined by RCS reduction higher than 10 dB. The proposed MS and its application to backward RCS reduction of high-gain antenna may promote the uses of metamaterials to many real-world applications.

Characteristic Mode Cancellation Method and Its Application for Antenna RCS Reduction

This letter proposed a characteristic mode cancellation method for design of an antenna radar cross section (RCS) reduction. Two kinds of subarrays whose unit cells are composed of a square patch with a circle hole and a cross patch, respectively, are designed. With the characteristic mode theory, the currents represented by the characteristic modes of two subarrays flow in an opposite direction. By arranging two subarrays into a checkerboard patterned array, cancellation of their characteristic modes is achieved and, thus, the resultant RCS of the whole array is greatly reduced. The checkerboard array is integrated with a microstrip antenna to reduce its RCS. The simulated and measured results are in good agreement and show that with the checkerboard array, the operating band of the reference microstrip antenna covering 8.32–9.32 GHz keeps unchanged, and the −10 dB broadband RCS reduction both in band and out of band of the microstrip antenna is from 6.4 to 21.4 GHz with an in-band gain increase of 1 dB.

A miniaturized absorbed frequency selective surface based on square resistor ring with low radar cross section

AbstractA miniaturized absorbed frequency selective surface based on square resistor ring is proposed in this research. This miniaturized absorbed frequency selective surface composed of a periodically arranged unit structure, and each unit structure is formed by an upper square resistor ring and a lower frequency selection surface. The structure has a good wave transmission performance from 1 GHz to 2 GHz, and the absorption rate is higher than 90% over the whole Ku band. At the same time, the structure can achieve a monostation radar cross‐section reduction of more than 10 dB covering the whole Ku band. Due to the miniaturized design of this structure, it has the property of eliminating the grating lobes in the absorption band when irradiated by oblique incident waves. Based on ensuring good transmission, it can realize broadband and wide‐angle antenna radar cross section reduction.

Ultrawideband High-Efficiency 2.5-Dimensional Polarization Conversion Metasurface and Its Application in RCS Reduction of Antenna

A linear-to-linear 2.5-dimensional polarization conversion metasurface (2.5-D PCM) with a high polarization conversion ratio (PCR) in ultrawideband is proposed. The unit cell of the 2.5-D PCM is composed of a superstrate etched with metal strips and a substrate attached with a metal ground. The 2.5-D PCM can efficiently convert the polarization of x -polarized or y -polarized wave to its cross direction after reflection. The PCRs are higher than 96% within a relative bandwidth of 99.5% for the x - and y -polarized vertically incident waves. In addition, the 2.5-D PCM can be applied to reduce the in-band and out-band radar cross section (RCS) of different antennas. A circularly polarized antenna is chosen as an example. Compared to the reference antenna, the monostatic and bistatic RCSs of the proposed antenna are decreased in an ultrawideband without the performance degradation of the antenna. The prototypes of the 2.5-D PCM and the antennas are fabricated, and the measurements are in reasonable accordance with the simulations.

A novel reconfigurable FSS applied to the antenna radar cross section reduction

Active reconfigurable FSS using pin diode for the antenna radar cross section (RCS) reduction is proposed. The reconfigurable FSS reflector is presented in this article. The proposed reconfigurable FSS reflector is able to be switched between band-stop FSS with OFF-state diodes and band-pass FSS with ON-state diodes around 3.8 GHz. The using of band-stop FSS reflector corresponds to the out-band RCS reduction during radar operating, and the using of band-pass FSS reflector corresponds to the in-band RCS reduction during radar nonoperating. Therefore, the state of the antenna scattering can be switched according to the working state of radar. The results show that the reconfigurable FSS reflector can contribute to the switchable RCS reduction between in band and out band of the antenna. The radiation performance of the antenna is preserved when the diodes are ON state. The monostatic RCS of the antenna with FSS reflector with ON-state diodes can be reduced more than 25 dB at operating band, and the out-band RCS reduction can be achieved with ON-state diodes.

Wideband radar cross section reduction of a microstrip antenna with square slots

AbstractThis paper proposes a new radar cross section (RCS) reduced microstrip antenna incorporating 475 square slots on the patch. The proposed antenna achieves wideband RCS reduction with radiation performance sustained. The modified and reference antenna are simulated and analyzed in radiating and scattering mode, respectively. Prototypes of two antennas are fabricated and measured. Compared with the reference antenna, the simulated result shows the modified antenna RCS reduced in the frequency range 1.1–2.6 GHz, which contains the in-band and out-of-band frequency band simultaneously. And the maximum RCS reduction is 7.6dB at the frequency of 1.19GHz. Besides, the modified antenna can achieve the antenna RCS reduction in the case of oblique incidence. The prototypes of two antennas are fabricated and measured, and the accuracy of the simulation is proved by the measured result. Due to its advantages of simplicity, wideband RCS reduced, broad-angle RCS reduced, the method in this paper is suitable for wideband antenna RCS reduction in space-limited environment.

Analysis and design of an ultra-thin metamaterial absorber and its application for in-band RCS reduction of antenna

ABSTRACTThis paper presents the analysis and design of an ultra-thin metamaterial absorber (MA) for the in-band Radar Cross Section (RCS) reduction of a patch antenna. The proposed MA consists of a periodic array of double square loop structures printed on an FR4 substrate with a thickness of 0.022 λo. A detailed theoretical analysis of the MA unit cell is conducted to investigate the absorbing characteristics of the MA. The simulated and measured results show that MA significantly reduces the RCS of the proposed antenna within its impedance bandwidth and a maximum RCS reduction of 15 dB is achieved at 6.75 GHz. The impedance bandwidth of the proposed antenna is 6.6–7 GHz, which is also improved by the loading of the MA. The results also show that after loading the MA on the patch antenna, the RCS of the proposed antenna is significantly reduced and there is no degradation observed in its radiation properties.

Wideband Polarization Conversion Metasurface for RCS Reduction of Antennas

Polarization conversion metasurface (PCM) with wide operating band and high polarization conversion ratio is proposed for antenna radar cross-section (RCS) reduction. A 3rd-order quadrate fractal structure (QFS) is designed as the PCM element that the polarization conversion ratio is greater than 80% from 10.45 GHz to 32.15 GHz (relative bandwidth of 101.9%). The PCM is applied in the RCS reduction of microstrip antennas by chessboard-like arrangement on the antenna. The performances of the proposed PCM and antenna are studied by measurement and simulation. The results show that, with the radiation performance hold, the monostatic RCS of the proposed antenna is obviously reduced from 8 GHz to 28 GHz which completely covers the operating band of the antenna.

A Novel Reflectarray Antenna with Reduced RCS

A novel frequency selective surface (FSS) configuration in the reflectarray antenna is proposed for reduction of radar cross section (RCS) level in this work. Double-layer FSS structure is located behind the reflectarray antenna as a ground. A 9 9 elements FSS with variable size patches has same geometry with the reflectarray antenna. The RCS reduction performance of reflectarray antenna both ground plane backed and FSS backed is compared. The results of simulation are obtained by using CST Microwave Studio. The simulation results show that RCS level of FSS backed reflectarray antenna is reduced both in-band (8-12 GHz) and out-of-band (2-7 GHz and 13-18 GHz). In the literature, RCS reduction of reflectarray antenna with FSS structure has only been achieved out-of-band. Furthermore, the gain and radiation performance of the ground plane backed reflectarray antenna and FSS backed reflectarray antenna are compatible with each other.

Reconfigurable polarization rotation surfaces applied to the wideband antenna radar cross section reduction

A reconfigurable polarization rotation surface (PRS) using chessboard-like geometry is introduced for the radar cross section (RCS) reduction of a Yagi-Uda antenna in this article. The reconfigurable PRS reflector can be switched between low-RCS PRS reflector and metal reflector. When the reconfigurable PRS reflector with ON-state diodes is used in the Yagi-Uda antenna, the antenna has a similar radiation characteristic compared with Yagi-Uda using metal reflector. The PRS reflector can be used to achieve a low-RCS characteristic reflector by chessboard configuration with OFF-state diodes. Finally, the status of RCS can be switched according to the working state of diodes. The results show that the radiation performance of the Yagi-Uda is preserved. The monostatic RCS of the Yagi-Uda using PRS reflector with OFF-state diodes can be reduced more than 25 dB.

3-D Absorptive Frequency Selective Reflector for Antenna Radar Cross Section Reduction

A methodology for designing a frequency selective reflector with two-sided absorption bands is proposed. This method is based on utilizing multimode resonators inside a 3-D unit cell to obtain an absorption-reflection-absorption response. Detailed analysis of this 3-D absorptive frequency selective reflector (AFSR) is provided with the aid of an equivalent circuit model to reveal the operating principle. To show the benefit of the new structure in antenna’s radar cross section reduction (RCSR), a dual-polarized 3-D-AFSR integrated with monopole and dipole antennas are simulated, fabricated, and then measured. Compared with their counterparts with normal ground plane, AFSR-backed antennas have shown a remarkable out-of-band RCSR. The −10 dB RCSR has fractional bandwidths of at least 64.7% and 41% with center frequencies of 3.4 and 8.3 GHz, respectively. The radiation characteristics of AFSR-backed antennas are nearly maintained. The realized gains are enhanced by 0.9 and 2.3 dB for monopole and dipole antennas mounted on a 3-D-AFSR, respectively.