A Compact SSPPs Unit With Bandpass Feature and its Application in Bandpass Transmission Line

In this letter, a novel spoof surface plasmon polaritons (SSPPs) bandpass filtering unit (BP-FU) is proposed. The equivalent circuit model of BP-FU is given and by establishing its ABCD-matrix, the pass band and forbidden band are analysed theoretically, which behaves the feature of bandpass. Meanwhile, the simulated dispersion curve of BP-FU shows bandpass feature. Subsequently, the proposed BP-FU is applied to design a bandpass filtering transmission line (TL). The TL obtains the bandpass filtering feature spontaneously due to the periodically arranged BP-FUs. The TL consisting of BP-FUs can be excited by the methods like exciting traditional unit and a transverse magnetic wave propagates along the TL. The field characteristic is as same as classical SSPPs TL. The measured results of the prototype of the TL shows a passband from 6.66 GHz to 10.06 GHz and ultrawide stopbands ( $\vert S_{21}\vert \lt $ -22 dB) from nearly 0 GHz to 5.36 GHz and 10.89 GHz to 40 GHz. The measured results indicate good application prospect in single conductor multifunction circuit.