Equivalent Circuit-Aided Miniaturized High-Q Frequency-Selective Rasorber

Abstract

This letter proposes an equivalent circuit-aided novel design of a highly selective and miniaturized absorption-transmission–absorption (A-T-A) frequency-selective rasorber (FSR). The idea of incorporating low-frequency resonators in the absorptive circuit is utilized for realizing a miniaturized broadband absorber. Further, the LC circuit resonator is studied and incorporated with the equivalent circuit model, leading to a transmission pole through the front resistive network. Correspondingly, a Minkowski fractal (MF)-shaped loop resonator is proposed on the top layer, which is capable of realizing a transmission pole in concurrence with the operating frequency of the bottom bandpass layer. The proposed FSR is a 2-layer design realizing high selectivity ( $Q{=}24.14$ ) at the passband of 9.9 GHz, which makes it the most suitable candidate for shielding/radar cross section (RCS) reduction applications of the narrowband radiating systems. Moreover, the proposed rasorber also exhibits compact size ( $0.015{\lambda }_{L}^{2}$ ), less thickness ( $0.081{\lambda }_{L}$ ), and wider absorption bands (3.7–9.3 GHz and 10.6–15.9 GHz in the lower and upper bands, respectively), in comparison with the existing literature. Furthermore, in the proposed FSR, the passband can be varied from 9.2 to 12.3 GHz by tuning the parameters of resistive and bandpass layers. A $25\times 25$ array prototype is fabricated, and the results are experimentally validated.