A novel dual-band frequency selective surface with close band spacing at ka-band

In this work, a novel dual-band frequency selective surface (FSS) with closely band spacing operating at Ka-band is designed. This FSS is composed of four metallic slot layers. The top and bottom layers are two identical layers consisting of four Y-shaped slots in 90° rotation symmetry, while the middle two layers are obtained by rotating the outer layers 45°. This FSS exhibits two transmission bands, and both of them have a two-order band-pass response as well as a small band ratio of 1.16. Meanwhile, there are two transmission zeros between two passbands, forming a transition stop-band with a Quasi-elliptic response. It makes these two closely spaced transmission bands have great isolation.