Compact Dual- and Triple-Wideband Filters Using Interdigital Spoof Surface Plasmon Polaritons

A new interdigital spoof surface plasmon polaritons (SSPPs) unit is proposed to design dual- and triple-wideband filters in this letter. The dispersion properties of the proposed interdigital SSPPs are analyzed and indicating that the asymptotic frequency of the fundamental mode (Mode 0) of the transition SSPPs unit is higher than that of the first-order mode (Mode 1) of the transmission SSPPs unit, which provides the feasibility in the design of dual passbands using Modes 0 and 1 of the SSPPs simultaneously. Also, by adjusting the stopband between Modes 0 and 1 of the transition interdigital SSPPs unit reasonably, three passbands can further be constructed. For verification, dual- and triple-wideband filters are accordingly well designed, fabricated, and measured. Good agreement between the simulations and measurements validities the proposed structure and design method.