High Incidence Angle Stable First Order and Second Order Bandstop Frequency Selective Surfaces at Terahertz Regime

This paper presents new miniaturized unit cells at terahertz (THz) wave band for first order (FO) and second order (SO) bandstop filter response. The FO and SO FSSs exhibit excellent angular stability of the filter response with changes in incidence angles. The FO-FSS unit cell consists of cross loop dipole resonator (CLDR) and stubs loaded dipole resonator (SLDR). The structure shows a transmission zero (TZ) at 0.42 THz and its stopband bandwidth (BW) covers the frequencies 0.39 to 0.44 THz (12.1%). A low profile design approach is implemented to obtain the SO bandstop response with overall design consisting of three conducting layers separated by two dielectric substrates. In the stack geometry, the top and bottom metal layers are the FO FSS and middle layer is the metal grid layer. The geometry exhibits wide stopband BW between 0.35-0.49 THz (33.3%). Also, three reflection zeros (RZs) near the skirts of the sidebands improve the filter selectivity. As compared to previous works at the THz wave band, the designed FSS shows lesser shifts in resonance frequency with the variation of oblique incidences up to an angle of 70°.