A Planar and Subwavelength Open Guided Wave Structure Based on Spoof Surface Plasmons

A planar and compact open waveguiding structure based on spoof surface plasmon polaritons (SPPs) was demonstrated. For practicality, instead of the well-known wire medium, the uniaxial strip medium (USM) was proposed and used as the effective bulk material with a negative dielectric constant to support the spoof SPP modes. The relevant formulations, including the modal dispersion relations and the formulation for the waves in a multilayer anisotropic structure, are analytically presented in this paper. Interestingly, instead of taming and suppressing the spatial dispersion (SD), which had been done in most past studies, SD was exploited in the proposed structure to enhance the field confinement of the spoof SPP mode by approximately 41%. Moreover, the thickness of the USM slab could be reduced by 50%, using conductor backing and without perturbing the odd mode. This method and SD can help avoid electromagnetic interactions among various components of a multilayer printed circuit board structure and help miniaturize sensors or surface-wave waveguides in the microwave regime. In this study, the subwavelength thickness of the proposed structure was only 0.09 λ₀ at 1.34 GHz. Additionally, the propagation loss for such slow-wave structures has seldom been discussed analytically and quantitatively. In this study, through calculations and simulations, low attenuation constants in the spoof SPP propagation direction of the proposed structures were investigated. Finally, an experiment was conducted, and an extraction method for obtaining the required reflection spectrum from the measured S-parameter was developed.