Ultra-thin ultra-broadband metamaterial absorber based on impedance surface

Abstract

In this letter, an ultra-thin microwave metamaterial for ultra-broadband radar cross section (RCS) reduction is presented. In the unit cell, an impedance surface pattern with two split-square-loops is proposed to achieve broadband absorption and polarization conversion. Two FR-4 dielectric substrates are above and below the resistive pattern. This design exhibits 85% absorption from 3.8 to 19.2 GHz under normal incidence. The fractional bandwidth of 134% is realized by multiple resonances. The polarization conversion rate (PCR) of the design is above 0.3 in the operating frequency band. The proposed concept is proved by full-wave simulation and experimental measurements. The performance under oblique incidence are investigated. The surface current has been illustrated to analyze the absorption mechanism. This design is ultra-thin (0.079λ_L at the lowest operating frequency) with ultra-broadband RCS reduction performance and provides an alternative to the stealth application of satellite solar panels.

Introduction

Metamaterials (MM) refer to some special composite materials or structures, which can obtain the extraordinary physical characteristics that conventional materials do not have. These characteristics are achieved by the structural design of the unit cell in the periodic array, which formed MM. Many metamaterial absorber (MMA) designs with wide absorption bandwidth and ultra-thin structure have been reported in recent years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. These MMA structures are mostly consisted of one or more layers of metallic patches or impedance surfaces with specific patterns and a ground metal plane separated by a dielectric substrate. The pattern is excited to form a surface current for absorbing. Ultrathin MMA with an absorption bandwidth exceeding 130% is relatively rare now.

For polarization converters, RCS reduction is generally achieved by adjusting the phase of the reflected waves. By arranging the unit cells of the polarization converters with a high PCR into several sections with orthogonal orientations, a chessboard surface with low RCS is formed [19], [20], [21].

The stealth of solar panels is essential to stealthy satellite as the solar panels occupy a large area after deployed. Satellites are primarily detected by ground-based radar, which requires the stealth materials used on the back of the solar array. When used on satellites, MMA is more suitable than polarization converters. For satellite applications, the RCS reduction performance of stealth materials is highly required, as well as their thickness, adaptability to the space environment and reliability.

An ultrathin microwave metamaterial for satellite application is proposed in this paper. The design achieved a bandwidth of 134% for at least 85% absorption with a thickness of 0.079λ_L. A prototype of the design is fabricated and measured.