Miniaturized Bandpass Filter Based on High-Order Mode of Spoof Surface Plasmon Polaritons Loaded With Capacitor

In this article, we propose a kind of new miniaturized cutoff tunable spoof surface plasmon polaritons (SSPPs) cell and design a bandpass filter (BPF) using high-order mode of this SSPP cell. The proposed new SSPP cell is miniaturized by adding a branch structure at the open end of the stub and bending the waveguide structure at the short end of the stub. For the designed BPF, by opening the rectangular slot in the stub and controlling the length and width of the rectangular slot, the upper cutoff frequency and the lower cutoff frequency can be tunable, respectively. Moreover, loading a capacitor between the stubs can further adjust the upper cutoff frequency of the BPF. Compared with the conventional SSPP unit, the area of the unit is reduced by 36.8%. The total tunable frequency range of the filter designed in this article reaches 1.91 GHz, and the return loss remains below −10 dB in the passband from 6.03 to 10.03 GHz.