A Dual-Polarized Wideband Frequency-Selective Rasorber With Low in-Band Insertion Loss and High Oblique Incidence Stability

A novel design of a dual-polarized rasorber with an interabsorption transmission band is proposed. The design consists of a lossy frequency-selective surface (FSS) at the top and a lossless bandpass FSS at the bottom. The two FSS layers are separated by an air spacer. The lossy FSS consists of lumped resistor loaded cross dipole elements connected to an outer ring resonator with a slotted circular patch inside. The lossless FSS consists of a square slot. The series resonance of the lossy FSS contributes to absorption, whereas the parallel resonance of the lossy FSS and the parallel resonance of the lossless FSS together contribute to transmission. The proposed design provides a bandwidth with the reflection coefficient below $-$ 10 dB from 2.89 to 8.85 GHz, corresponding to a fractional bandwidth (FBW) of 101.5%. It has a thickness of 0.096 $\lambda _{L}$ ( $\lambda _{L}$ is the wavelength corresponding to the lowest cutoff frequency of the bandwidth with the reflection coefficient below $-$ 10 dB). The rasorber also shows a $-$ 1-dB transmission band from 6.1 to 7.19 GHz (FBW 16.4%) with a minimum insertion loss of 0.44 dB at 6.6 GHz. It exhibits quite stable absorption and transmission characteristics up to 45 $^\circ$ angle of incidence. The operating principle of the rasorber is discussed using an equivalent circuit model. Experimental validation of the rasorber performance is also done. Good agreement between the measured and the full-wave simulation results is observed.