Spoof Surface Plasmon Polariton-Based Continuously Tunable Cutoff Frequency Filter

In this letter, a continuously tunable cutoff frequency filter is proposed, which is composed of tunable spoof surface plasmon polaritons (SSPPs) loaded with p-i-n diodes and varactor diodes. The dispersion behavior of the unit structure can be controlled by switching the SSPP unit with a p-i-n diode, accomplishing reconfigurability at two cutoff frequencies of 6.51 and 7.68 GHz. In order to realize more tunable cutoff frequencies, a new unit structure that can obtain a cascaded combination of varactor diodes and p-i-n diodes is presented. The simulated and measured results verify that the cutoff frequency of the filter can be tuned continuously from 5.34 to 7.23 GHz by controlling the magnitude of the biasing voltage, and the relative tunable bandwidth of the SSPP filter is up to 70.8%.