Generation of Millimeter-Wave Nondiffracting Airy OAM Beam Using a Single-Layer Hexagonal Lattice Reflectarray

In this letter, a millimeter-wave (mm-wave) nondiffracting Airy orbital angular momentum (OAM) beam is experimentally demonstrated by using a single-layer hexagonal lattice reflectarray based on an Airy-OAM-phase modulation method. To reduce the design time, a near-field synthesis technique is used to theoretically analyze the nondiffracting characteristics of the Airy OAM beam. A hexagonal dual-resonance element, composed of a hexagon ring around a square patch, is employed in the reflectarray to provide a linear phase range of 360°. The proposed reflectarray with a diameter of 45 cm is designed at 47 GHz, which can reshape the incident wave according to the superposition phase of the desired Airy beam and OAM beam. To validate our design, a prototype is fabricated and measured. The measured results agree well with the theoretical and simulated ones. The experimental results show that an Airy OAM beam with the mode of $+$1 is successfully generated from 44 to 49 GHz. The nondiffracting propagation distance is greater than 2.5 m (392λ0). Moreover, the measured results validate the autofocusing and self-healing properties of the Airy OAM beam.