Transition From Surface Cavity Mode to Cavity Mode in Deep-Grooved Parallel Plate Waveguide

The parallel plate waveguide (PPWG) is an excellent device for guiding and controlling at terahertz wave. When a deep groove is integrated into a PPWG, only the surface cavity mode is excited, which limits its applications in filtering and sensing. In this paper, we demonstrated that in a double deep-grooved PPWG, both fundamental and higher-order cavity modes can be observed. Our experimental and simulation results show that the effective groove depth of the fundamental cavity mode in the bottom deep groove can be efficiently increased by cutting another shallow groove in the top metal plate, facing the bottom deep groove. In addition, the transition from the so-called surface cavity mode to traditional cavity mode can be observed with increasing depth of the shallow groove. These results may have applications in the multichannel filtering and sensing field.