Metasurface base on uneven layered fractal elements for ultra-wideband RCS reduction

Abstract

A novel metasurface based on uneven layered fractal elements is designed and fabricated for ultra-wideband radar cross section (RCS) reduction in this paper. The proposed metasurface consists of two fractal subwavelength elements with different layer thickness. The reflection phase difference of 180° (±37°) between two unit cells covers an ultra-wide frequency range. Ultra-wideband RCS reduction results from the phase cancellation between two local waves produced by these two unit cells. The diffuse scattering of electromagnetic (EM) waves is caused by the randomized phase distribution, leading to a low monostatic and bistatic RCS simultaneously. This metasurface can achieve -10dB RCS reduction in an ultra-wide frequency range from 6.6 to 23.9 GHz with a ratio bandwidth (fH/fL) of 3.62:1 under normal incidences for both x- and y-polarized waves. Both the simulation and the measurement results are consistent to verify this excellent RCS reduction performance of the proposed metasurface.

Passive techniques for target radar cross section reduction: A comprehensive review

“…These metasurfaces have been designed by arranging meta‐particles with different sizes or various orientations in a pattern such that a broadband and wide‐angle RCSR has been fulfilled. The diffusion metasurfaces 96‐144 can be categorized into different groups realizing and focusing on some interesting functions and applications of them, such as polarization conversion metasurfaces 79,81,85,87‐89 (discussed in Section 2.2), Mantle Cloaks, 139‐141 checkerboard metasurfaces based on phase cancelation, 101,137,138,144 coding and digital metasurfaces, 99,100,116‐118,120,121,126,129,131,134‐136,143 phase gradient metasurfaces, 103,104,115,142 and hybrid metasurfaces 100,107‐109,142 . Various arrangements of these metasurfaces were proposed to backscatter the incident waves to arbitrary areas away from the receiver direction.…”

“…Haji‐Ahmadi et al 120 designed a pixelated checkerboard metasurface by two unit cells (square patches) on a double‐layer substrate based on the pixilation and optimization of a square patch for ultra‐wideband 10‐dB RCSR of 95%. Su et al 143 presented a novel metasurface composed of uneven layered fractal elements. In this method, two fractal elements with different layer thickness were arranged in a large configuration by applying 1‐bit coding sequences which led to an ultra‐wideband RCSR from 6.6 to 23.9 GH (113%).…”

“…The second metric mentioned in Tables 1 and 3 is the simulated monostatic RCSR. The passive cancelation techniques used for RCSR are mostly simulated by two famous simulation softwares called Ansys‐high frequency structure simulator (HFSS) 44,58,60,62‐65,70,71,74,84,88,96,111,112,116,135 and CST Microwave Studio 22,25,54,62,75,103‐109,113,120,128,134,137,143,146‐148 . As all the approaches of Table 1 except 63 and some of the methods (checkerboard surfaces) of Table 3 are based on the phase cancelation technique achieved by phase difference of almost 180° ± 37°, a setup is utilized for full‐wave simulation of unit cells to determine the reflection coefficient characteristics such as phase and amplitude.…”

“…Additionally, most of them have been performed only for monostatic RCSR at normal incident angle ignoring the wave polarization. Hence, nowadays, the modern passive techniques and structures based on phase cancelation or destructive interference using surfaces including frequency selective surface (FSS), 52‐55 EM band gap (EBG), 56‐59 artificial magnetic conductor (AMC), 47,48,60‐77 polarization rotation reflective surface (PRRS), 78‐95 metasurfaces, 96‐145 and hybrid methods, 146‐149 receive a lot of attention to improve the mentioned conventional techniques and overcome their limitations. In the recent decades, researchers have made a lot of efforts on these modern passive RCSR techniques and numerous works have been proposed and completed in order to achieve a system similar to the ideal RCSR system.…”

Recent developments of metamaterials/metasurfaces for RCS reduction

“…Recently, applications of metamaterials and metasurfaces for low-observation platforms have attracted enormous interests due to their unusual properties [38][39][40][41][42][43][44][45][46][47][48]. Without considering signal distortion, these radar cross section (RCS) reduction technologies can be generally classified into three categories according to respective working principle: metamaterials/metasurfaces for electromagnetic wave (EMW) cloaking, scattering, and absorbing.…”