A 2.5-D Miniaturized Frequency-Selective Rasorber With a Wide High-Transmission Passband

This letter presents a 2.5-D frequency-selective rasorber (FSR) with a wide high-transmission (|S
₂₁
| <; 1 dB) passband and two absorption bands. The proposed FSR consists of a 2.5-D lossy layer and a lossless layer, between which is an air gap. At the top layer, a 2.5-D convoluted resonator, which introduces large equivalent impedance to generate a wide high-transmission passband, is constructed in the center of lumped-resistor-loaded T-type metallic strips. A triple-layer bandpass frequency-selective surface is adopted as the lossless layer. Procedures to develop the accurate equivalent circuit model, aiming at providing physical insights into the operating mechanism of the proposed 2.5-D FSR, are discussed. The simulation results indicate that the proposed FSR has a 1 dB transmission band from 7.81 to 11.78 GHz with 40.53% relative bandwidth and 80% absorption bands covering 3.67-6.80 GHz and 13.74-15.31 GHz. A prototype of 2.5-D FSR is fabricated and measured to validate the design.