Compact bandpass filter with ultra-wide stopband based on spoof surface plasmon polaritons for sub-6G application

In this paper, a newly ring-shaped spoof surface plasmon polaritons (SSPPs) structure is proposed for the construction of bandpass filter (BPF) with combing the short-circuited stubs (SCSs). Compared with the conventional rectangular-shaped SSPPs unit, the proposed ring-shaped SSPPs unit has a relative lower cutoff frequency at the same periodic unit size. Moreover, the high-order modes of the ring-shaped SSPPs unit at different height are disperse distribution, which allows it to realize wide stopband suppression. The lower and upper cutoff frequencies of the passband can be respective controlled by structural parameters of SCSs and SSPPs unit. By properly adjusting the height of SSPPs units in conversion parts, a balanced performance between the passband and ultra-wide stopband suppression can be achieved. For verification, a BPF with the frequency from 2 GHz to 5 GHz for Sub-6G application and the stopband reaching 30 GHz is designed. The experimental show that the measured results agree well with the simulated results, validating the proposed structure and design method. The fabricated filter only occupies 1.13 lambda g x 0.23 lambda g, exhibits the advantage of compact size.