Broadband bandpass filter with double‐layered spoof surface plasmon waveguide as main transmission line.

In this article, double‐layered spoof surface plasmon waveguide (DLSSPW) which consists of double‐layered metal gratings is used as a main transmission line for realizing a broadband bandpass filter with a center frequency of 1.5GHz and a relative bandwidth of 80%. Four equally spaced short‐circuited double‐stripped lines are used as resonators and mounted on the main transmission line. Efficient conversion from the quasi‐transverse electromagnetic (TEM) waves in the coplanar waveguide to spoof surface plasmon polaritons (SSPPs) in the DLSSPW is achieved by using gradient double‐layered metal gratings and sector‐structure impedance matching circuit. This filter has lower insertion loss than using single‐layered spoof surface plasmon polaritons, as the DLSSPW has tighter field confinement and lower radiation loss. Moreover, due to the slow‐wave effect of DLSSPW, the main‐part length of the filter is shorter than microstrip‐form counterpart by 30%. The measured S‐parameters of the plasmonic bandpass filter agree well with the simulated ones, validating the good features. [ABSTRACT FROM AUTHOR]