Thin magneto-dielectric coatings for hybrid-mode horn antennas

Hybrid-mode horns such as corrugated horns, strip loaded horns and dielectric loaded horns have been used for satellite antennas due to their low cross-polarized radiation. Furthermore, horns that support the balanced hybrid-mode can behave as either soft or hard horns, providing low sidelobes or high aperture efficiency. Although corrugated horns have found wide use in satellite antennas, dielectric loaded horns are less desirable because of their higher mass, dielectric losses, and limited bandwidth. Recently, a metamaterial-based hybrid-mode horn design was proposed, where a metamaterial liner with dielectric constant less than unity was placed on the wall of the horn. It promises improved bandwidth as well as low manufacturing costs. In fact, metamaterials can exhibit a much broader range of electromagnetic properties, such as a negative or near zero index of refraction. In this work, a magneto-dielectric metamaterial liner with low refractive index was used to realize hybrid-mode horns. This paper provides metamaterial design principles and the expressions needed for hybrid-mode operation, as well as examples of conical horn antennas with metamaterial coatings that exhibit low cross-polarized radiation.