Modal analysis of a double-layer line waveguide inside and outside the homogenization regime

The dispersion features of the line wave supported by a double-layer line-wave waveguide with a cross section exhibiting central symmetry are determined through full-wave simulations of a truncated structure and a numerical post-processing fitting procedure. Within the low-frequency homog-enization regime, in which the unit cell of the constituent metasurfaces is a small fraction of the free-space wavelength, the phase constant of the line wave is thus retrieved rigorously. The adopted approach has been also extended to higher frequencies beyond the homogenization limit, where higher order space harmonics become non-negligible, the line wave is thus to be regarded as a Bloch mode of a periodic structure, and the associated stopband regimes are shown to emerge.