Transformation Optics-based Antenna for Focusing OAM Beams

In this article, a metamaterial horn antenna based on transformation optics (TO) is presented to generate a focused orbital angular momentum (OAM) beam. By applying the coordinate transformation, a metamaterial insertion inside the horn is designed to concentrate the radiated OAM beam. The TO-based insertion is further realized by using split ring resonators (SRRs). The metamaterial antenna is fabricated and measured to verify the design. A 13o reduction in the main lobe angle is realized in measurement by SRRs.