Wideband modal analysis of a double-layer line-wave waveguide. dispersive properties and radiative effects

A broadband modal analysis of a double-layer line-wave waveguide constituted by two center-symmetric pairs of inductive and capacitive metasurfaces is presented, with the aim of characterizing the dispersive and radiative properties of the relevant line-wave mode both inside and outside the metasurface homogenization limit. To this aim, a finite length of the waveguide, excited at both ports through suitable microstrip transitions, is first simulated with a commercial solver. Then, a numerical fitting of the field along the waveguide axis is performed using exponential functions, in order to retrieve the wavenumbers and excitation coefficients of the modal line wave and of its higher order space harmonics. The latter results are validated through an independent Bloch analysis of the unit-cell ABCD matrix, retrieved through simulations of truncated structures constituted by a finite number of unit cells The proposed approach facilitates an original wideband reconstruction of the line-wave dispersion curves, including bound and peculiar surface and space leakage regimes, as well as stopbands both in bound and radiative regions. Radiation patterns associated with the latter are also reported, having the form of elliptically polarized fan beams with the expected frequency scan in elevation.