Inhomogeneous metasurfaces with engineered dispersion for broadband hybrid-mode horn antennas

Metamaterial and metasurface structures, which satisfy the balanced hybrid conditions, have been recently proposed for designing hybrid-mode soft and hard horn antennas. In this paper, we present the design of broadband soft metasurfaces and their applications in hybrid-mode conical horns. These designs exhibit surface characteristics that can be controlled by adjusting the constituent structural elements. The analysis and design of metasurfaces were performed on both a planar platform and in a cylindrical waveguide structure. Such dispersion-engineered metasurfaces with customized surface properties can support the desired hybrid modes in a cylindrical waveguide, facilitating their usage in horn antennas. By engineering the metasurfaces with regard to their surface impedance as well as tailoring their spatial distributions along the wall of the horn, we demonstrate an inhomogeneous metahorn with superior performance and broader bandwidth compared to those with uniform liners. The symmetric far-field radiation patterns with low sidelobe and cross-polarization levels, together with the corresponding aperture field distributions, signifies the hybrid-mode operation of the horn, validating the efficacy and broadband performance of the metasurfaces. Such metasurface-lined horns can be employed as soft feeds in dual polarization antenna systems.