A Band-Pass Filter Based on the Spoof Surface Plasmon Polaritons and CPW-Based Coupling Structure

In this paper, a band-pass filter based on the spoof surface plasmon polaritons (SSPPs) and coplanar waveguide (CPW)-based coupling structure is proposed. The design concept of the proposed band-pass filter is to use the SSPP structure and CPW-based coupling structure for controlling the high cut-off frequency and filtering the low-frequency wave, respectively, which means that the low and high cut-off frequencies of the band-pass filter can be independently controlled. The physical mechanism of the proposed band-pass filter is explained with the aid of dispersion curves, electric field distributions, and equivalent circuits. Moreover, parametric studies are conducted to analyze the effects of the key parameters on the controllable performance of the band-pass filter, which is useful for practical designs. Furthermore, in order to improve the high-frequency performance, the split ring resonators are added to the structure. The simulation results show that the proposed band-pass filter achieves a bandwidth (for $\vert \text{S}_{11}\vert < -10$ dB and $\vert \text{S}_{21}\vert > -1.6$ dB) of 35.9% (7.31–10.51 GHz). The experimental results validate the proposed concept and measured results are in a good agreement with simulated ones, which indicate that the proposed band-pass filter is believed to be significantly promising for further developing plasmonic functional devices at microwave frequencies.