Spoof Surface Plasmon Polariton Based on Stepped Grooves and Its Application in Compact Low-Pass Filter Design

In this paper, stepped slot-type grooves are utilized to develop coplanar waveguide (CPW) spoof surface plasmon polariton (SSPP) transmission lines (TLs). The equivalent circuit model is developed to analyze the effect of the stepped slot-type grooves. And it is found that all the three proposed SSPP TLs exhibit lower asymptotic frequency and more compact size than conventional SSPP TLs based on uniform grooves. Moreover, the dispersion features can be controlled flexibly by changing the impedance ratio of the stepped slot-type grooves. And among the three proposed SSPP TLs (Type A, Type B, and Type C), Type C SSPP TL has the most compact size. Consequently, based on Type C SSPP TL, an ultra-compact plasmonic low-pass filter (LPF) is designed to validate the design theory. Good agreement is observed between the simulated and measured results for which reflection coefficient is lower than − 10 dB in passband from 0 to 1.73 GHz and good shape factor of 1.09 for the transition from the passband to the stopband. Besides, the proposed plasmonic low-pass filter occupies very compact size, indicating that the proposed plasmonic filter can find potential applications in compact plasmonic system design.