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Polarisation‐insensitive dual‐band transmissive rasorber designed on a single layer substrate

: In this study, a frequency selective surface (FSS)-based rasorber has been proposed by combining the designs of split-ring absorber and dual bandpass FSS, which are printed on the front and backside of 0.8-mm thick FR-4 substrate, respectively. The proposed FSS-based rasorber is a thin single layer structure and also exhibits the polarisation-insensitive behaviour due to its four-fold symmetry. The split-ring structure at the front contributes to the resonant absorption at 6.2 GHz, while the bandpass FSS structure at the backside provides two transmission windows at 3.1 and 8.4 GHz, respectively. The parameters of the design are optimised such that at the absorption frequency, the bandpass FSS acts as a complete metallic ground. The operating principle of the proposed rasorber is analysed using an equivalent circuit model. The effects of design parameters on the performance of the rasorber are studied, and accordingly an optimum range of lower and upper transmission bands with respect to the absorption band are determined. A 21 × 21 array of the proposed rasorber unit cell is fabricated, and the results are experimentally verified.