Spoof plasmonic waveguide developed from coplanar stripline for strongly confined terahertz propagation and its application in microwave filters

A novel planar terahertz (THz) plasmonic waveguide developed from coplanar stripline (CPS) is proposed for the first time to achieve strongly confined THz propagation performance based on the concept of spoof surface plasmon polaritons (SSPP). Guided-wave characteristics of the proposed plasmonic waveguide are theoretically investigated by eigen-mode simulation technique and finite-difference time-domain solutions. It is found that the waveguide propagation characteristics can be directly manipulated by designing the SSPP unit cells, which exhibit flexible tuning ability of the asymptotic frequency and strong THz field confinement. The idea has been validated through fabricated filter experiments in microwave frequency regime by scaling up the geometry size of the proposed structure. The measured results illustrate high performance of the ultra-wideband filter, in which the reflection coefficient is better than -10 dB from 3 to 13.1 GHz with the smallest and worst insertion losses of 2.2 dB and 5.6 dB, respectively. This work presents a new SSPP waveguide developed from CPS to realize the THz-wave propagation with strong field confinement, which may have promising potential applications in various integrated THz plasmonic devices.