A miniaturized high-selectivity frequency selective rasorber based on subwavelength resonance and interdigital resonator

A miniaturized high-selectivity frequency selective rasorber (FSR) with subwavelength resonance and interdigital resonator, which exhibits low insertions loss in passband and two high absorption bands at both sides of one passband, is investigated. The FSR consists of a lossless layer and a lossy layer. The lossy layer is made by a periodic arrangement of cross-dipoles with resistive sheets loaded on both sides of the interdigital resonator. The lossless layer is a bandpass, subwavelength resonant, frequency selective surface composed of three layers of metal in the shape of squares and crosses. An equivalent circuit model is proposed to analyze its operating principle. A meandering procedure is used in conjunction with subwavelength resonance and interdigital resonator to achieve miniaturization of the FSR. The unit cell dimensions are 0.087λL× 0.087λL× 0.1λL (λL being the free-space wavelength at the lowest operating frequency). Additionally, the designed rasorber has the property of high selectivity due to the subwavelength resonance. Under normal incidence, an insertion loss of about 0.21 dB is obtained at 10.25 GHz, the fractional bandwidth for -10 dB reflection is about 94.5%, and the -3 dB transmission relative bandwidth is 15.7%. The FSR shows a stable response over a wide range of incidence angle of 30° for both transverse electric (TE) and transverse magnetic (TM) polarizations. A prototype of designed FSR has been manufactured and measured, showing a reasonable agreement with simulations.