Programmable Multifunctional Device Based on Spoof Surface Plasmon Polaritons

The spoof surface plasmon polariton (SPP) waveguide, which could support well-confined surface waves along an ultrathin corrugated metallic strip, is one of the most advantageous candidates in integrated circuits due to the remarkable properties of low crosstalk, low loss, and packaging minimization. Many devices based on the spoof SPP waveguide have emerged, but it is still a challenge to manipulate the SPP waves freely in real-time. Here, we propose a programmable multifunctional spoof SPP device by loading varactor diodes between adjacent metallic teeth of SPP waveguides. By programming the bias voltages of the varactor diodes dynamically, the coupling waves propagating on two SPP waveguides can be freely controlled. Simulations and experiments demonstrate that the programmable SPP device can realize high-efficiency SPP through transmission, unequal coupling, 3 dB direction coupling, and crossover transmission with better isolation effect. Different functions and operational frequency ranges can be reconfigured in real-time. The proposed method lays the groundwork for applications in large-scale microwave integrated circuits and digital communication systems.