Frequency selective rasorber with large frequency ratio dual passbands and ultra-wideband absorption

This paper presents a frequency selective rasorber (FSR) featuring a large frequency ratio (FR) dual passbands and ultra-wideband absorption. Existing dual-passband FSRs are typically limited by small frequency ratios (FR) and narrow absorption bandwidths, restricting their application in large FR dual-frequency integrated antenna systems. To overcome these limitations, the proposed FSR cascades two lossy layers with a low-complexity frequency selective surface (FSS). The FSS layer is based on a slot-type single passband FSS, and dual passbands with a large FR are achieved by incorporating T-shaped slots, while the lossy layers decouple the high- and low-frequency passband resonators by physically separating them with absorbing resonant structures, allowing them to independently determine their respective passband frequencies. Furthermore, cascading two lossy layers with distinct resistances ensures ultra-wideband out-of-band impedance matching. Experimental results demonstrate dual passbands at 11.64 GHz and 28.21 GHz with a large FR of 2.42 and low insertion losses of 0.92 dB and 0.88 dB, respectively. The design achieves an overall absolute absorption bandwidth of 20.26 GHz, comprising two bands with fractional bandwidths of 116.70% and 62.57% for absorptivity greater than 80%. The measured results align well with simulations, confirming the effectiveness of the proposed method for high-performance stealth radomes.