A compact microwave bandpass filter based on spoof surface plasmon polariton and substrate integrated plasmonic waveguide structures

A compact microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures based on substrate integrated plasmonic waveguide (SIPW) and spoof surface plasmon polariton (SSPP) is proposed and investigated. The dispersion and transmission characteristics of the proposed unit-cell structures of SSPP and SIPW were analyzed numerically, respectively. Numerical results indicate that the high and low cut-off frequencies of the bandpass filter can be independently adjusted by changing geometric parameters of unit-cell structures of SSPP and SIPW, respectively. The proposed microwave bandpass filter has a smaller electrical size because of its better electromagnetic (EM) field constraints than the traditional SIW ones with combed groove lines SSPPs. To verify the design method and concept, a microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures has been designed, fabricated, and measured. The results demonstrate that the proposed passband is in the range of 7.3–10.1 GHz, the return loss is higher than 10 dB and the insertion loss is less than 2 dB. The microwave bandpass filter is very compact in size, only about 0.99 λ0 × 0.35 λ0, where λ0 is the wavelength at the center frequency.