Dual-Band Bandpass Frequency-Selective Structures With Arbitrary Band Ratios

A new type of dual-band bandpass frequency-selective structure (FSS) with arbitrary frequency band ratio is presented. The proposed FSS features a 3-D composite topology, which consists of an array of three-layer parallel strip lines with inserted metallic rods, and two identical single-layer patch arrays. With a special arrangement of these periodic arrays, two independent propagation paths, including multimode resonators with different resonant frequencies, are constructed under a linearly polarized incident wave, thus providing dual-band performance. Two operating frequency bands can be independently designed because these two paths can be equivalent to two separate inductor-loaded transmission lines. The operating principle is first explained by analyzing the electric field distributions at resonant frequencies. Based on this, an equivalent circuit model is then established to further understand the mechanism. A group of parametric studies are also conducted to investigate the filtering performance. In order to verify our design concept, two practical examples with large and small band ratios are fabricated and measured. The unique feature of the kind of dual-band FSS is that it can exhibit stable dual-band performance with both small and large band ratios under a large variation of incident angle.