Vortex Beam Generation and Mode Conversion using Spiral-phase Transmitarrays

This paper presents a concept to generate vortex beams and their inter-mode conversion into each other using transmit arrays (TAs) consisting of circularly polarized elements. The novel circularly polarized unit-cell operates between 22.5-23.5 GHz of the ka-band. The novel presented unit cell has a compact profile and composed of three identical metallic sections which are placed on top and between a double-layer dielectric substrate. The designed TAs are composed of 12 × 12 elements, in which each unit-cell is rotated individually in order to generate the related phase distribution of the desired vortex mode. Through rotation of the unit-cells a full 360-degree spiral phase progression on the TA can be obtained. Using several TAs with different phase distributions, the mode of the resultant propagating vortex wave can be changed in space. The simulated results for vortex beams of modes 1, 2, and 3 show desirable inter-mode conversion.