Design of a wideband rasorber with a polarisation-sensitive transparent window

In this study, the authors present a thin wideband electromagnetic planar absorber for X-and Ku-band, which also has a polarisation-sensitive transparent window at frequencies lower than L-band. The design is based on a two-layer capacitive circuit absorber with the back-metal layer replaced with a polarisation-sensitive frequency-selective surface. The structure is studied for normal incident waves with two orthogonal linear polarisations. The authors optimised the structure to gain high transparency at low frequencies for one of the polarisations and at the same time good absorption efficiency for both polarisations at the high-frequency band. For one of the polarisation a -1.9 dB transmission with the transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarisation, the authors obtained more than 3:1 (100%) bandwidth of -19 dB absorption. The transmission loss is significantly reduced compared to the authors' earlier design based on Jaumann absorber. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials shows that the design is robust.