Hybrid spoof surface plasmon polariton and substrate integrated waveguide bandpass filter with high out-of-band rejection for X-band applications

Abstract

Two bandpass filters based on hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) are presented for X-band applications, herein. The dispersion and transmission characteristics of the proposed hybrid SSPP-SIW structures are analysed, and the influence on the variation of their structural parameters is investigated. The proposed dumbbell-shaped SSPP shows more slow-wave effects than the rectangle-shaped SSPP for the same height of grooves, and hence could be a good choice in the design of compact, low loss and highly integrated microwave and terahertz devices. The lower and upper cut-off frequencies of hybrid SSPP-SIW bandpass filters can be adjusted independently by varying the structural parameters of SIW and SSPP units, respectively. The proposed two filters exhibit excellent passband (8–13.15 GHz for filter I and 8–13.5 GHz for filter II) and wide upper-band rejection (>42.5 dB from 14.1 to 20 GHz for filter I and >41 dB from 14.2 to 19.5 GHz for filter II) simultaneously. Their size is very compact, amounts to only about 1λg × 0.7λg, where λg is the guided wavelength in the SIW at the centre frequency.