Three-Dimensional Dual-Band Frequency Selective Surface With Close Band Spacing

A novel dual-band three-dimensional (3-D) frequency selective surface (FSS) based on square coaxial waveguides (SCWs) is proposed. The unit cell of the proposed 3-D FSS contains one modified parallel-plate waveguide (MPPW) propagation path and one SCW propagation path. The MPPW path is created by employing a centered via hole. Thus, two transmission poles are produced by odd- and even-mode coupling. The third transmission pole was generated by the square slot resonance in SCW path. After properly adjusting the location of three poles, two passbands with close band spacing are obtained, and the band ratio is 1.31. Owing to the E-filed vectors in different paths are out of phase at the output port, two transmission zeros are introduced for improving frequency selectivity. The E-field analysis of the transmission zeros/poles is presented to explain the operating principle of the proposed 3-D FSS. The simulated results show that the FSS exhibits a stable response to variations of incident angle from 0° to 45° for both TE and TM polarizations.