Reconfigurable broad-band rejection filter based on spoof surface plasmon polaritons

In this paper, we describe a new approach for constructing a broad-band tunable rejection filter based on reconfigurable spoof surface plasmon polaritons (SSPP) whose center frequency can be tuned by altering the capacitance of a varactor diode. The filter structure is composed of SSPP waveguide with double split-rings. We have analyzed and discussed the dispersion characteristics of the filter unit structure and S-parameters of the filter. The filter's rejection band can be tuned in real-time within the frequency range of 6.4 GHz-10.2 GHz, the rejection strength can reach a positive effect, and the transmission loss in the passband can also be less than 2 dB. When a varactor diode was loaded with the same capacitance, the filter produced one rejection band, and when the varactor diode was loaded with two sets of capacitances, the filter produced two rejection bands. From the results, the filter expands microwave communication possibilities. Furthermore, SSPP structures deliver better field confinement and more substantial field augmentation than standard approaches (microstrip filters), which is beneficial for many communication system applications.