Analysis, Reduction, and Utilization of Loss in Reconfigurable Spoof Surface Plasmon Polaritons

Reconfigurability of dispersion properties of spoof surface plasmon polaritons (SSPPs) have been realized by loading tunable elements such as varactors and p-i-n diodes. However, the parasitic resistance of tunable elements will lead to transmission loss of SSPPs, which still lacks investigation. In this article, we propose to comprehensively answer three critical questions in this area: 1) how to analyze the loss of reconfigurable SSPPs; 2) how to reduce the loss of reconfigurable SSPPs; and 3) how to utilize the loss of reconfigurable SSPPs. For the first question, the complex characteristic impedance of reconfigurable SSPPs is theoretically obtained, which indicates the mechanism of the enhanced loss in reconfigurable SSPPs. For the second question, a low-loss reconfigurable SSPP structure loading parallel varactors is proposed to reduce and reconfigure the loss of reconfigurable SSPPs. For the third question, a multifunctional 2-unit antenna array is designed and tested using a feeding network composed of the loss-reconfigurable SSPPs. Experimental results demonstrate that two functions of sum-difference beam forming and amplitude modulation are achieved by the single sample. Thus the technique of loss reconfiguration in SSPPs may find wide applications in efficiency-sensitive circuits and smart microwave systems in the future.