Double-Sided Parallel-Strip Line Resonator for Dual-Polarized 3-D Frequency-Selective Structure and Absorber

Double-sided parallel-strip line (DSPSL) resonator is employed in the unit cell (UC) of a 3-D frequency-selective structure (3-D FSS) in order to exhibit the desired response (bandstop, bandpass, and absorption) under an incident wave of arbitrary polarization. It is found that this UC supports the propagation of three quasi-TEM modes. The first and third modes are concentrated in the substrate and air regions of the UC, respectively. While the second mode is concentrated in the interface between air and substrate of the UC, the polarization of the second mode is perpendicular to the polarization of the first and third modes. Detailed analysis of these propagating modes is provided with equivalent circuit models to explain the operating principle. A dual-polarized bandstop 3-D FSS is then proposed. It exhibits a stable frequency response with a constant out-of-band bandwidth under a large range of oblique incidence angle. A dual-polarized absorber is also realized employing a UC with DSPSL resonator. By properly exciting and absorbing the second mode of the modified UC, an ultra-wideband absorber is constructed, which has -10 dB fractional bandwidth of 148% from 1.51 to 10.1 GHz with an absorber thickness of 0.1 lambda(0) at the lowest absorption frequency.