Dual-band filter design based on hourglass-shaped spoof surface plasmon polaritons and interdigital capacitor structure

In this paper, a dual passband filter with spoof surface plasmon polaritons (SSPPs) and interdigital capacitance structure loaded on a coplanar waveguide (CPW) is proposed. Firstly, the hourglass-shaped SSPP unit-cell structure and the interdigital capacitor structure are introduced on the coplanar waveguide transmission line to obtain high fractional bandwidth and low insertion loss passband characteristics. Then, a dual passband filter is formed by loading the interdigital capacitor loop resonator to excite the trapped waves. The simulation results show that the proposed dual passband filter has excellent upper sideband rejection and dual passband filtering performance. The fractional bandwidths of the two passbands of the design are 46.8% (1.49-2.40 GHz) and 15.1% (2.98-3.63 GHz), respectively, which can achieve more than -40 dB rejection in the range of 4.77-7.48 GHz. The upper and lower cutoff frequencies of the two passbands can be independently regulated by changing the structural parameters of the proposed filter. In order to gain a deeper understanding of the operating principle of the dual passband filter, the corresponding dispersion curves and electric field distribution, LC equivalent circuit analysis are given. Finally, the prototype of the designed filter is fabricated according to the optimized parameter values. The experimental results are in good agreement with the simulation ones, indicating that the proposed dual-passband filter is of great importance in microwave integrated circuit applications.