On the Equivalent-Circuit-Based Design of Double-Lossy-Layer Wide Transmissive Rasorbers with Ultrawide Reflection Suppression Band

In this paper, a double-lossy-layer frequency-selective rasorber (FSR) with an ultrawide reflection suppression band is presented based on the equivalent circuit approach with a clear, concise, and effective design process. First, the general equivalent circuit model (ECM) of double-lossy-layer FSRs is established and studied to reveal the mechanism of the operation band extension of the absorption-transmission (A-T) FSRs to the lower frequency. Second, a single-polarized FSR is designed inversely based on the optimized circuit parameters to fulfill the ideal desired performances. The evolution process is exhibited step-by-step and the equivalent-circuit-based design guideline is summarized. Simulation results show the single-polarized FSR achieves a low reflection band (|S ₁₁ | ≤ -10 dB) from 1.07 GHz to 12.66 GHz, with a ratio bandwidth of 11.83:1. The 80% absorption band covers 0.99-7.11 GHz (151.1%) and the -1-dB transmission bandwidth is 43.0%, ranging from 7.97 GHz to 12.33 GHz. Then, a dual-polarized FSR is further presented and optimized to preserve excellent frequency responses. In addition, the proposed FSR also achieves ultra-miniaturization and thus improves angular stability partly. Finally, a dual-polarized FSR prototype of 20 × 20 unit cells is fabricated and measured to verify the design and the measurement results coincide well with the simulation ones.