Substrate Integrated Waveguide Wideband Bandpass Filter Based on Spoof Surface Plasmon Polariton

Based on the analysis of the dispersion characteristics of substrate integrated waveguide (SIW) and spoof surface plasmon polariton (SSPP), two hybrid planar SIW-SSPP wideband bandpass filters are designed using the high-pass characteristics of SIW and low-pass characteristics of SSPP to achieve flexible upper and lower sideband control as well as ultra-wideband characteristics. The first filter is an ultra-wideband bandpass filter designed based on the hybrid SIW-SSPP structure, in which the upper and lower cutoff frequencies can be independently controlled by adjusting the structure parameters of the SSPP unit and SIW unit, respectively. The passband ranges from 6.75GHz to 11.88GHz, and the return losses are all less than -11.5dB. The second filter is an improved version of the first filter, in which a pair of complementary splitring resonators are introduced on the front and back of the substrate to insert a transmission zero within the passband, achieving the characteristics of dual passbands. The return losses are all less than -15dB. Simulation results show that the designed filters have sharp out-of-band rejection, compact structure, and good filtering performance, which proves their feasibility.