A Broadband and High-Efficiency Compact Transition From Microstrip Line to Spoof Surface Plasmon Polaritons

Spoof surface plasmon polaritons (SSPPs) have been considered as a new-type surface wave transmission line (TL) because of its single line feature. However, it cannot be directly fed by the measured system because the transmission mode of SSPP TLs is totally different from the traditional TLs like microstrip lines. Also, the existing solutions require complicated structures and a big area on the circuit space to complete the transition between the two different propagation modes. Here, we propose an ultracompact and simple transition from the microstrip line to the SSPP single-conductor TL, consisting of a very short section of gradient corrugations and a specially designed flaring ground etched on the bottom side of the SSPP TL. Numerical simulations show a good agreement with the experimental results, showing high transmission efficiency for the proposed transition in a broad relative bandwidth from 4.5 to 11.5 GHz. Moreover, this SSPP feeding prototype is easy to migrate to other single-conductor SSPP devices.