Dual-mode high-gain OAM array based on nested metasurface with simplified feeding network

In this letter, a high-gain dual-mode orbital angular momentum (OAM) antenna array with a simplified feeding network based on polarization rotating metasurface is presented. To circumvent the complexities of the conventional vortex wave array feeding network while achieving dual-mode vortex wave generation simultaneously, an array consisting of a dual-polarized concentric feed array (CFA) and a concentrically nested transmission metasurface is developed. The CFA is employed to generate dual-polarized electromagnetic waves irradiating the metasurface. Unlike the traditional uniform circular array, the proposed CFA is excited by equal amplitude and phase without specific phase requirements. The transmission-mode metasurface can achieve polarization selectivity by incorporating polarization rotation units. With the combined effect of the feed and metasurface, good isolation between the two OAM modes is generated. A prototype generating +1 and +2 OAM mode is simulated, fabricated, and measured to demonstrate the design method. The proposed design has advantages such as a simple feeding structure, easy fabrication, high gain, low profile, and high isolation. Moreover, the proposed antenna can carry different information in different OAM modes separately, which is a promising candidate antenna for mode multiplexing OAM communications.