Wideband Circularly Polarized Dual-Mode Vortex Beams Reflectarray Design Using Dual-Semi-Split-Loop Elements

In this letter, a wideband circularly polarized reflectarray composed of 30 × 30 unit cells is proposed to generate dual-mode vortex beams. The element consists of two back-to-back semi-split-loop structures printed on the FR-4 substrate, an air layer, and a metal ground plane. The two back-to-back semi-split-loop structures provide the multiresonance property, which can effectively increase the bandwidth. A 360° phase range is achieved by changing the spatial orientations of the element. Based on the proposed element and the superposition design method of aperture field, a dual-mode square aperture vortex beams reflectarray is simulated, fabricated, and experimentally demonstrated. The measured results confirm that two vortex beams carrying +1 and -1 mode of orbital angular momentum are successfully generated in a wide range of frequencies from 5 to 8 GHz. The size of the proposed reflectarray is 75 cm × 75 cm, and the measured maximum gain is 22.2 dBic. The measured 1 dB gain bandwidth is 33.3%.