A Switchable Low‐Pass to Band‐Pass Filter Based on Spoof Surface Plasmon Polaritons

In this letter, a spoof surface plasmon polariton (SSPPs)‐based filter, which can be tuned between low‐pass and band‐pass function is proposed. The low‐pass characteristic is generated by the periodic structure of SSPPs. Meanwhile, the band‐pass function is achieved by introducing metal vias in the SSPPs unit cells. PIN diodes and bias circuits are used to control the switching between low‐pass and band‐pass performance. The equivalent circuit model is established by transmission line theory and transfer matrix to analyze the filtering mechanism. A prototype of the SSPPs filter is fabricated, and the measured S‐parameters show 3 dB bandwidth from 0 to 8.63 GHz for low‐pass mode and from 4.63 to 8.46 GHz for band‐pass mode. The measured results show good agreement with the simulated ones, which indicates the designed filter has potential applications in the field of communication.