Multibeam OAM Transmitarray With Stable Vortex Property Based on Bifocal Method

In this letter, a multibeam transmitarray carrying orbital angular momentum (OAM) is introduced to realize 1-D +/-30° beam coverage. A three-layer unit cell is designed to provide high-efficiency transmission and full 360° phase coverage. This unit cell consists of two orthogonal polarizers at the outermost layers and a polarization rotating patch in the middle layer. A feeding array is employed to illuminate the transmitarray. By combining bifocal principle with the method of OAM beam generation, the stability of steered OAM beams is improved compared to conventional single focal design. A five-beam protype producing -1 OAM mode is simulated, fabricated, and measured, realizing a +/-30° beam coverage with stable vortex property and high mode purity. The proposed design has advantages such as multi-OAM-beam, stable vortex property, wideband, high gain, and easy fabrication.