Miniaturized spoof surface plasmon polaritons low-pass filter with a novel transition structure

In this letter, a miniaturized spoof surface plasmon polaritons (SSPPs) low-pass filter with a novel transition structure is proposed. The novel transition structure is designed by two rectangular strips with an inclination of 17° and right-angled triangle patches. In this letter, we analyzed the normal and azimuthal components of the electric field perpendicular to the plane of the filter at different locations, verifying the effectiveness of the transitional structure. Besides, efficient conversion between quasi-transverse electromagnetic (TEM) waves and transverse magnetic (TM) polarized SSPPs waves are achieved by loading the novel transition structures. The designed filter can suppress unnecessary radiation loss and increase transmission efficiency. More importantly, the filter size is 47.52 mm $\times7.47$ mm and its length is reduced by at least 61% compared with the other low-pass filters with the same cutoff frequency. This letter has promoted the development and application of SSPPs low-pass filter and related equipment in microwave frequencies.