Achieving subwavelength field confinement in sub-terahertz regime by periodic metallo-dielectric waveguides

In this paper, we report on a periodic metallo-dielectric structure that supports geometry-induced surface plasmons in the sub-terahertz regime. The proposed structure is made up of a dielectric-coated metallic grating sandwiched by parallel metal plates. Based on the modal analysis of 2D and 3D structures, the impact of a metal cladding and a customized dielectric coating on the dispersion relation and field distribution of the guided surface wave is investigated. It is found that modal field confinement is improved in the presence of a metal cladding without narrowing the operational bandwidth of the waveguide. Moreover, a customized subwavelength-sized dielectric coating based on high-resistivity silicon (HR-Si) can further improve the confinement. As a result, by incorporating both the HR-Si coating and the metal cladding in a conventional metallic grating, subwavelength field confinement is achieved over nearly a 2:1 frequency bandwidth. The achieved performance makes the realization of extremely-low radiation loss sharp bends possible. In particular, the achieved radiation loss is less than 0.5dB for a 90° bend of radius λ₀/4 based on a waveguide cross-sectional dimension of almost λ₀/10 where λ₀ is the free-space wavelength at the maximum frequency of operation. The proposed waveguide is promising for the implementation of sub-terahertz guided-wave devices and circuits thanks to its outstanding field confinement and ruggedized and shielded structure.