This paper presents the design of a phase gradient metasurface lens (MSL) that enables the orbital angular momentum (OAM) beam convergence alleviating the limitations of the OAM beams in far-field wireless communication. An MSL of a specific constitutive electromagnetic parameter, i.e., relative refractive index, in front of a traditional Uniform Circular Array is designed at 10 GHz. In the presence of the lens, the beam converges from 58∘ to 24∘ for +1 and –1 OAM modes. The proposed MSL can also be used for second-order (±2) OAM modes. The experimental verification performed on the laboratory prototype agrees well with the simulated results. The purity analysis also confirms that the OAM beams passing through the lens maintain high mode purity, thereby not disturbing the phase distribution in the corresponding OAM modes. The designed lens can be used in point-to-point and defense communications.
