Restoring the radiating performances of shortened horn antennas over a broad frequency range

We propose a flat metamaterial-based lens to be applied to the aperture of a shortened horn antenna in order to achieve gain performances similar to the ones of the corresponding optimum horn over a broad frequency range. In order to achieve an uniform phase distribution at the horn aperture and maximizing, thus, the gain, the central part of the lens consists of a conventional epsilon-positive material and the part closest to the metallic edges of the horn consists of an epsilon-near-zero material, i.e. a wire-medium. Due to the different phase delay of the field at the edges of the aperture on the E- and H-plane, two different wire-mediums are properly designed in order to compensate the phase delay on both planes and achieve the highest possible gain enhancement . As an example, we report the design of the proposed lens for a C-band pyramidal horn. The length of the horn is half the length of the optimum horn, while the obtained gain performances are similar to the ones of the optimal horn over the entire mono-modal frequency band of operation of the feeding waveguide. This result may open the door to several interesting applications in satellite and radar systems.