Miniaturized Lossy-Layer Scheme For Designing a Frequency Selective Rasorber

This letter proposes a miniaturized frequency selective rasorber (FSR) based on parallel-plate capacitors that can be applied in antenna systems to delay the appearance of grating lobes. Compared with traditional solutions, the lossy-layer unit-topology is rearranged to balance a more efficient capacitor <italic>C</italic><sub>1</sub>, fewer resistive lumped elements, and a large inductance <italic>L</italic><sub>1</sub> in series. Furthermore, the lossless layer is constructed using a third-order frequency selective surface with parallel-plate capacitors. These approaches achieve a rasorber unit size of only 0.035<italic>λ</italic><sub>L</sub>, where <italic>λ</italic><sub>L</sub> is the wavelength of the lowest absorption frequency. Under normal incidence, the 1 dB transmission band with a bandwidth of 40.9% is obtained at 6 GHz, whereas an absorption rate of over 90% covers 1.5 to 4.05 GHz. Moreover, the FSR exhibits high stability for the dual-polarization and oblique incidence up to 30°. Prototypes were fabricated and measured, verifying the feasibility of the miniaturized design.