3-D dual-band FSSs based on multiple square coaxial waveguides

Abstract

In this paper, a kind of dual-band three-dimensional (3-D) frequency selective surfaces (FSSs) based on multiple square coaxial waveguides (SCWs) are proposed. Through a simple design, two transmission poles are intrinsically produced by the square slot resonances in two SCW propagation paths, and another transmission pole is generated by a parallel-plate waveguide (PPW) propagation path. With the help of these three transmission poles, a closely-spaced dual-band 3-D FSS can be achieved with the band ratio 1.118. In order to further extend the application of the proposed structure, a modified design is then exhibited. One pair of short SCW resonant elements is created in each SCW propagation path. As a result, each SCW propagation path can provide two transmission poles for a flat passband by the odd-and even-mode coupling. Moreover, the transmission zeros are located at each sides of passbands, leading to both-sided sharp roll off. The unit cell size of the modified design is reduced remarkably. The E-field analysis of transmission zeros/poles is given to explain the operating principle of two proposed FSSs. The simulated results show that the proposed FSSs can achieve stable responses to variations of incident angle from 0° to 45° for both TE and TM polarizations.