A Compact Filter Based on Spoof Surface Plasmon Polariton Waveguide for Wide Stopband Suppression

An spoof surface plasmon polaritons (SSPPs) bandpass filter (BPF) supported by trident-shaped complementary grooves is proposed in this letter. Compared with the traditional rectangular-groove SSPP unit cell, the vertical size of the proposed SSPP unit cell is reduced by 40% under the condition of the same asymptotic frequency. Then, a matching feeding structure is introduced by designing microstrip-to-slotline transition (MST) and thus a low cut-off frequency can be obtained. The low cut-off frequency of the passband is determined by the MST structure and the high cut-off frequency of the passband is determined by the SSPP structure. Consequently, a BPF with controllable frequency band and wide stopband suppression is formed by the MST structure and the proposed SSPP structure. Finally, the designed BPF was fabricated and measured. Both numerical and experimental results suggest good filtering performance of the proposed BPF in the frequency band from 2.1 to 8 GHz.