An Ultra-Wideband Radar Absorbing Material Including a Decoupling Layer

In this article, an ultra-wideband radar absorbing material is presented. The proposed design approach focuses on the realization of a multilayer structure consisting of two lossy layers separated by a lossless low-pass FSS filter. By including the lossless filtering FSS, a significant enhancement of the absorbing bandwidth can be accomplished since the operation of the two lossy layers is decoupled in frequency. In detail, the top lossy layer, operating from 6 to 18 GHz, features a resistive square loop unit cell with a surface resistance of 30 Ohm/Sq. Conversely, the bottom one is constituted by a Jerusalem cross unit cell with a surface resistance of 15 Ohm/Sq covering the 2-6 GHz band. The decoupling layer is conceived as a metallic square patch unit-cell, implementing a typical low-pass response. The design procedure for each layer is thoroughly analyzed, and full-wave simulations are performed to verify the performance. Numerical results demonstrate that the proposed ultra-wideband absorber achieves a -10 dB absorption band ranging from 2 to 18 GHz, corresponding to a 160% fractional bandwidth. Additionally, the structure shows a considerably reduced overall thickness, i.e. 14.5 mm, leading to a compact design. Therefore, these remarkable capabilities position the proposed method as a valuable asset within broadband and passive radar absorbing materials.