A dual-band bandpass filter based on hybrid ESPPs-SIW structure with ultra-wide upper stopband suppression

In this paper, a new bandwidth-controllable dual-band bandpass filter (BPF) based on hybrid effective surface plasmon polaritons (ESPPs) and substrate integrated waveguide (SIW) structure is presented. It consists of three parts, where a dual-band filtering part is realized by a two-layer SIW and an air cavity located on the top of SIW, and two traditional SSPPs low-pass filtering parts are introduced for wide stopband suppression. According to effective-medium theory and structural dispersion, different widths and relative permittivities of the SIW and air cavity are used to provide flexible cutoff frequencies of the ESPPs-SIW structure, thus exhibiting independently controllable bandwidth. The simulation results reveal that the presented dual-band BPF has outstanding filtering performance and ultra-wide upper stopband suppression level. The upper stopband can be extended up to 21.4 GHz (8.5 f 0 ) with a suppression level of −20 dB, where f 0 is the center frequency of the first passband (i.e., 2.52 GHz). The measurement results are in good agreement with the simulation results, which verifies the correctness of our design concept and method.