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.