Continuously-Tunable Low-Loss Phase Shifter Using Weak-Dispersion Spoof Surface Plasmon Polaritons

We propose a continuously tunable low-loss phase shifter based on weak-dispersion spoof surface plasmon polariton (SSPP) waveguide. Unlike traditional designs of SSPP devices that rely on the strong-dispersion property, we address the high insertion loss issue by leveraging the weak-dispersion region of SSPP. A detailed study reveals the relation between the waveguide length, phase shift, and insertion loss of SSPP. Based on the weak-dispersion SSPP structure, we design an active SSPP unit by integrating a varactor to tune the phase continuously. Experimental results show that continuous phase shifts up to 258° are achieved with an insertion loss less than 0.016 dB per degree at the designed frequency of 8.5 GHz. Compared to the traditional phase shifters, the proposed design exhibits significant performance.