Miniaturized suspended strip-line bandpass filter based on spoof surface plasmon polaritons

In this letter, we propose the design of miniaturized suspended strip-line (SSL) filters based on spoof surface plasmon polariton (SSPP), a sub-wavelength mode confined tightly around artificial structures. To avoid using high-density lossy dielectric fillings, we place a periodic corrugated metallic strips (PCMS) structure in a rectangular metallic cavity. Two probes are positioned near the two ends of PCMS structure. Since PCMS structure support SSPP with shorter wavelength, it can be treated as low-loss artificial dielectrics with high permittivity epsilon(r) equivalently. The cut-off frequency f(l)(ower) waveguide modes in the cavity will be reduced, which, plus the cut-off frequency f(upper) of SSPP, will produce a pass band between f(l)(ower) and f(upper). Due to high epsilon(r), low insertion loss and light weight of the PCMS structure, miniaturized band-pass filters can be implemented using such a configuration. We demonstrated a prototype operating a bandpass filter in 2.7-4.6 GHz. The cross-section of cavity is reduced by more than 75%. The filter is with quite low insertion loss only 0.1-0.3 dB. Both simulation and measurement results verify this design. This work provides an alternative to miniaturized, light-weight, high-efficiency SSL filters.