Design of Filtering Tunable Liquid Crystal Phase Shifter Based on Spoof Surface Plasmon Polaritons in PCB Technology

In this article, a new design approach for tunable filtering phase shifters on the basis of liquid crystal (LC) materials is reported. This proposed filtering LC phase shifter (LCPS) based on spoof surface plasmon polaritons (SSPP) simultaneously provides self-embedded fixed filtering performance and continuously tunable phase shifts. Equivalent circuit analysis and transmission parameter representations are implemented for the expounding of the fixed stopband caused by split-ring resonators (SRRs). Furthermore, due to the slow wave characteristics of SSPP waveguide, the higher tuning rate and figure of merit (FoM) can be intrinsically realized, which reveals that it can realize miniaturization and decrease insertion loss for specific phase shifts. In the end, the prototypes are designed, fabricated, and measured. The fabrication methodology of printed circuit board (PCB) technology ensures the mechanical stability, flexible design, perfect packaging, and low cost. The measurement results show the proposed bandstop filtering LCPS not only exhibited the fixed stopband from 7.61 to 8.18 GHz owning larger than 20-dB attenuation but also achieved the FoM more than 10.1°/dB from 6 to 7.45 GHz and more than 15.2°/dB from 8.37 to 10 GHz, which effectively verifies the theoretical analysis.