The Research on a FSS with High Roll-Off Characteristics Based on SIW

In this letter, a frequency selective surface (FSS) unit with high roll-off characteristics was designed by cascading and branching two substrate-integrated waveguide cavities (SIWCs) of different sizes. The metal surfaces at the top and bottom of the unit feature periodic slits. The coupling between the aperture resonance and the resonances within the two cavities can generate two transmission zeros, forming a sharp lower sideband and a sharp upper sideband. The structure is depicted in Figure 1 (a-e), where the cross slots on the top and bottom surfaces are of the same dimensions, and the coupling slots in the middle layer are cross slots of different sizes, with all elements in each layer having the same periodicity [1]. The typical response of an SIWC-FSS with a single cross slot, similar to the response of an SIWC-FSS with lattice or square ring slots [2]. It can excite both aperture and cavity resonances simultaneously. By adjusting the coupling between these two different resonances, the transmission zeros can be easily controlled at the lower or upper sidebands. The slot lengths of the single SIWC-FSS with either lower or upper sharp sidebands are the same, but the cavity sizes differ. Therefore, by combining two such SIW cavities in a periodic unit, a highly selective FSS with two sharp sidebands can be achieved.