Dispersion-engineered broadband frequency-selective rasorber without external lossy loads

Conventional frequency selective rasorbers (FSRs) rely on the combination of a frequency selective surface (FSS) and a lossy layer, either for a 3D structure or a stacked 2D configuration. Typically, the lossy layer is implemented by loading lossy materials or lumped elements, which tend to constrain the operating bandwidth, increase structural complexity, and reduce design flexibility. Consequently, there is a growing demand for more novel design paradigms that eliminate the reliance on external lossy loads. One promising approach is to merge the regulation of surface plasmon polaritons (SPPs) with spatial waves. In this work, dispersion engineering of spoof surface plasmon polaritons (SSPPs) is employed to design a broadband FSR free of external lossy media loading. By strategically tailoring the dispersion characteristics of the fundamental mode and higher-order modes of a nested structure, a transmission window with two absorption bands on both sides can be achieved. As proof, an FSR sample is fabricated and tested. Under normal incident electromagnetic (EM) waves, the proposed FSR exhibits an absorptivity of over 80% in the frequency ranges of 6.85-10.55 GHz (42.5%) and 21.88-29.1 GHz (28.3%). Additionally, the -1 dB transmission band, freely tunable by the nested dispersion characteristics, covers from 13.5 to 18.5 GHz (31.3%). What we believe this to be is a novel implementation scheme for FSR, based on SSPP dispersion engineering, offering valuable insights for mitigating the limitations imposed by external loads on the transmission band of FSRs and expanding the design concepts.