Metamaterial Horn Antennas
The first decade of the 2000s saw an abundance of research on electromagnetic metamaterials, including metamaterial surfaces, high-impedance surfaces , electromagnetic band-gap materials , and artificial magnetic conductors (AMCs) [20, 21], all of which have shown promise for a variety of antenna applications. As hybridmode horn antennas required boundaries characterized by their anisotropic surface impedances, the design techniques that had previously been developed for other antenna applications could be readily adapted to create metamaterial surface designs for hybridmode horns. Applying those surface designs to actual horn antennas requires numerous modifications and approximations, one of which is the fact that tapered horn walls do not permit the direct placement of a surface that was designed to be periodic in two dimensions. The following sections provide details and examples for many of the design considerations that are relevant to the development of metamaterial horn antennas, including successful metamaterial implementations of hybrid-mode horns.