Spoof Surface Plasmon Polariton Band-Stop Filter with Single-Loop Split Ring Resonators

A novel band-stop filter with single-loop split ring resonators (SRRs) is proposed for spoof surface plasmon polaritons (SPPs) at millimeter wave frequencies, achieving a miniaturized size of 0.052λ0×0.278λ0 at its resonant frequency. The SRRs provide both a low-pass response as the rectangular corrugations used in the conventional SPPs and an additional band-stop response induced by the resonance of SRRs. To verify this design, a back-to-back device with two co-planar waveguides as the input and output feeding was fabricated and characterized, the measured S-parameters of which agree well with the simulation. The measured stop band is centered at 49 GHz with a -10-dB bandwidth of 4.1 GHz and a high Q-factor of 93, in which the maximum attenuation is 31 dB. The filter has a low insertion loss of less than 2.8 dB in the pass band. Such approaches may find many applications to achieve compact millimeter wave circuits.