Generation of Ultra-Wideband OAM With Extremely High Purity and Near-Perfect Vortex Beams Based on Continuous Reflection-Type Meta-Grating

This article presents a novel continuous meta-grating array (MGA) for the generation of ultra-wideband, near-perfect orbital angular momentum (OAM) beams with extremely high mode purity. First, a novel dielectric-doping strategy is proposed to overcome the inherent narrowband characteristics of conventional grating atoms, resulting in an ultra-wideband dielectric-doping meta-grating atom (DDGA). By establishing an equivalent circuit model (ECM), the operational mechanism is analyzed. The design method is provided to establish clear DDGA design guidelines to follow. Simulation and ECM calculations reveal that within the 9.06–19.88 GHz (74.7%), the circularly co-polarized reflection coefficient and polarization conversion ratio exceed 99.7% and 98.7%, respectively. Subsequently, a space-variant sub wavelength MGA is generated using grating functions. The continuous grating array ensures the continuity of the reflected field, thereby avoiding beam distortions and low mode purity that may result from potential mutual coupling and diffraction effects caused by discontinuities in traditional metasurfaces. In the 9.0–21.0 GHz (80.0%), the MGA is capable of generating near-perfect vortex beams, ranging from low-orders to high-orders, with extremely high purity and very low mode crosstalk. In addition, it demonstrates frequency-aperture size insensitivity and dual-wideband properties, facilitating miniaturization and size customization while delivering high-performance OAM in the high-frequency 37–50 GHz. Finally, experimental validation confirms the effectiveness.