Wideband Dual-Mode Vortex Wave Metasurface Based on Distance Inversion Method

Vortex waves, leveraging the orthogonal properties of orbital angular momentum (OAM), are considered of great significance in high-capacity communication systems. However, available multifunctional vortex wave generators are often constrained by dispersion effects, limiting their operation to only a few frequency points or within narrowband. In this article, a method for generating dual-mode OAM vortex waves under broadband conditions is proposed. Initially, by employing the Pancharatnam-Berry (PB) phase concept, 360° coverage of the reflective phase can be achieved on a single dielectric substrate. Subsequently, to address the reduced purity of OAM modes caused by metasurface dispersion under broadband conditions, a distance inversion method is proposed. A prototype is designed, manufactured, and measured to demonstrate the effectiveness of the proposed method. Both simulated and measured results confirm that the metasurface can generate OAM beams with $l \,\, = \,\, -1$ and $l \,\, = \,\, +2$ within a bandwidth from 8 to 14 GHz (54.55% relative bandwidth). Across this frequency range, the measured OAM purities for $l \,\, = \,\, -1$ and $l \,\, = \,\, +2$ exceed 86% and 82%, respectively. The proposed metasurface exhibits potential application in high-capacity multiplexed wireless communication systems. Furthermore, the distance inversion method can mitigate the effects of metasurface dispersion and shows promise for broadband metasurface design, as well as wavefront manipulation.