Ultra-thin spoof surface plasmonic structure and its application to bandpass filter design

In this paper, the dispersions and electromagnetic wave transmission of higher-order modes in a kind of ultra-thin spoof surface plasmonic structures, the conformal surface plasmon (CSP) structure, have been explored at microwave frequency. The transmission spectrum shows a multi-passband characteristic. To eliminate the radiation loss associated with the higher-order modes, a ground plane is introduced to the CSP structure, and it is found that the dispersion curves and transmission spectrum exhibit the similar feature as that of the CSP structure without ground, but with much less radiation loss. The multiband transmission characteristic of the CSP structure has also been applied to design bandpass filter (BPF). It is found that by combining CSP structures with different groove depth the passband of the BPF could be tuned. The designed BPFs have been validated with both the full-wave simulations and the measurements on fabricated prototype at microwave frequency.