High-Directivity Orbital Angular Momentum Antenna for Millimeter-Wave Wireless Communications

Although orbital angular momentum (OAM) millimeter-wave wireless communications have attracted much attention given their potential to provide an additional degree of freedom in channel capacity, they still face challenges for realization. For instance, the OAM beam diverges rapidly in free space, limiting the coverage of wireless communication. To increase the communication range, we propose a high-directivity broad-bandwidth OAM antenna, which consists of a nonlinear taper and a lens-integrated metamaterial structure. A linearly polarized TE (transverse electric)11 mode traverses through the antenna to generate two OAM modes with the low reflectance of the metamaterial structure and a low divergence angle. We evaluate these two factors separately and analyze the effect of reducing the OAM divergence angle. Then, we validate the OAM antenna using the CST Microwave Studio software and experimentally verify its performance. The measured mode patterns are quantitatively analyzed using a cross-correlation function and by calculating the beam divergence angle from beam radius variations. The proposed OAM antenna provides a novel approach to effectively reduce the divergence angle of the OAM beam and may be suitable for realizing millimeter-wave wireless communications.