Mode Conversion of Multimode OAM Waves Based on Transmitted Metasurface

In this letter, a method of orbital angular momentum (OAM) mode conversion based on the principle of phase superposition is presented and analyzed. Utilizing this method, OAM waves can be modulated to a higher mode by secondary phase regulation on the vortex wavefront with fewer RF channels. To realize the multimode conversion operation, a transmitted metasurface with a feeding source of uniform circular arrays (UCAs) is designed. To simplify the feeding network design of UCAs, a center-feed circularly polarized microstrip patch is used to form dual loops UCAs as the primary feeding for generating +1/+2 OAM modes. In addition, a mode conversion transmitted metasurface (MCTM) carrying +1-order phase distribution is contrived and evokes the function of the second-layer phase regulation. Utilizing the simple dual loops UCAs configuration in conjunction with the flexible MCTM, higher-order mode OAM waves can be generated conveniently, and the OAM mode can be converted from +1/+2 to +2/+3 successfully. The measured results show a good agreement with the simulated ones, demonstrating that the proposed antenna provides an effective approach to achieving higher-order OAM waves using a limited source.