Multimode and Reconfigurable Phase Shifter of Spoof Surface Plasmons

Traditional phase shifters (PSs) are mainly focused on phase performance and rarely consider the phase shift between different electromagnetic (EM) modes, limiting their widespread applications. Spoof surface plasmon polaritons (SSPPs) support EM waves with strong field confinements, giving rise to the time delay of signals. Due to the flexible dispersion behaviors, SSPPs can be engineered at will by designing the plasmonic structure parameters. Benefitting from these characteristics, here we propose a multimode and reconfigurable SSPP PS loaded with varactor diodes. By controlling the dispersion behaviors, phase differences between different SSPP modes can be realized, and the phase shift of each mode can be reconfigured. Experimental results show that the proposed SSPP PS can achieve about 240°, 241°, and 340° phase shifts among the fundamental (even) modes, the high-order (odd) modes, and the fundamental and high-order modes, respectively, by switching the bias voltages applied to the varactors. Additionally, the proposed SSPP PS has the capability to continuously tune the phase difference in each mode. Simulations and measurements have a good consistency. This work lays the groundwork for SSPP applications in large-scale integrated circuits and wireless communication systems and has a promising application in Terahertz circuits.