A High Efficiency Band-Pass Filter Based on CPW and Quasi-Spoof Surface Plasmon Polaritons

A high efficiency and compact band-pass filter based on coplanar waveguide (CPW) is investigated in this paper, which lower and upper cut-off frequencies of the proposed filter can be tuned independently. In the proposed design, interdigital structure is used to filter the low frequency wave and a quasi-spoof surface plasmon polaritons (Q-SSPPs) structure is designed for tuning the higher cut-off frequency. The proposed Q-SSPPs structure contains only one cross-shaped element and keeps the similar properties of periodic SSPPs structure. The operating principle of the proposed design is explained by field distribution, dispersion curves, and equivalent circuits. The studies of vital parametric are carried out for better understanding the influences of the concerning parameters on the tunability. The simulated results indicate that the proposed design can obtain a wide bandwidth from 8.8 GHz to 17 GHz (about 63.6%) with high transmission efficiency (
$\vert S_{11}\vert < -15$
dB and
$\vert S_{21}\vert > -0.2$
dB). A prototype of the proposed design is fabricated and the measured results show good agreement with the simulated ones.