Surface Waveguide Topologies Supporting Both TM- and TE-Mode with the Same Phase Velocity

Authors: Mei Li, Shaoqiu Xiao, Jiang Long, and Dan Sievenpiper

Source: FERMAT, Volume 20, Communication 5, Mar-Apr., 2017

Abstract: Surface waveguides (SWGs) are a class of open-boundary structures with the capability of guiding surface waves which are intimately bound to the surface of the structure[1]. One of the most commonly occurring type is the planar structures consisting of periodic sub-wavelength elements. Due to the capability of controlling the propagation path of surface waves (SWs), SWGs have been employed for the applications of electromagnetic scattering alteration, cloaking, absorbing, as well as antenna applications in the terms of modulated reactance surfaces, holographic surfaces and lenses. An SWG structure supports SWs that are polarized in a transverse electric (TE) mode, a transverse magnetic (TM) mode, or a combination of a TM and a TE mode depending on the geometric structure of the surfaces[2]. SWG structures that support dominantly TM mode or TE mode have been studied for years and employed to design holographic surfaces for applications like leaky-wave radiation and field focusing. However, these structures are sensitive to the polarization and therefore limitations exist due to such polarization sensitivities. For example, it is challenge to get a centrally symmetric focused field when illuminated by a horizontally polarized field [3]. For holographic antennas, a narrow symmetric beam is also hard to achieve when excited by a horizontally polarized field. As a result, the aperture efficiency is reduced. Therefore, one significant challenge is to make a SWG structure that is insensitive to the polarization of given fields. In this abstract, we introduce two kinds of SWG topologies that can support both TM and TE modes with the same phase velocity [4]. The proposed SWG structures are constructed by a double-layer FSS. The top- and bottom-layer FSS of the first class SWG are formed by the isotropic periodic elements. The two layers can dominantly support TM mode and TE mode, respectively. For the second type of SWG topology, the top and the bottom layers have the same geometry and are rotated 90o with respect to the normal direction of the surface. In terms of the configuration of the each layer, the conducting strips are continuous in one direction and discontinuous in the other orthotropic direction. Therefore, for a single layer, it dominantly supports TM mode in one direction and TE in the orthotropic direction. In particular, a loop-wire ........

Index Terms: Surface waveguides, dispersion, periodic structures, artificial materials, surface waves

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Surface Waveguide Topologies Supporting Both TM- and TE-Mode with the Same Phase Velocity