Spoof surface plasmon polaritons developed from siw using ring slots and vias

A new type of spoof surface plasmon polaritons (SSPPs) developed from conventional substrate integrated waveguide (SIW) using ring slots and vias is proposed in this paper. The asymptotic frequency and lower cutoff frequency of the SSPP structure can be easily tuned by changing the width of SIW walls and radius of the ring slot, respectively. A trapezoidal microstrip line and a small ring slot are used for the efficient mode conversion to smoothly transit from microstrip line to the proposed SSPP structure. The presented SSPPs have a flat bandpass filtering response with adjustable center frequency and bandwidth. In order to better verify the transmission and cutoff characteristics, two bandpass filters using the proposed SSPPs with relative bandwidths of 61.7% and 76.4%, respectively, are fabricated and measured. Good agreement between the simulations and measurements verifies the proposed design idea.