A Wideband, Low-Profile, Bessel Beams OAM Generator Based on Rotated Differentially Transferred and Reflected Elements

In this communication, a wideband folded configuration for generating orbital angular momentum (OAM) vortex beams is presented. The Bessel beams OAM generator consists of a circularly polarized (CP) feed source, a transmitarray (TA) metasurface, and a reflectarray (RA) reflector. It is noteworthy that both the TA and RA elements feature a differential architecture, which significantly enhances broadband performance compared to traditional single-fed metasurface elements. By exploiting the Pancharatnam-Berry (PB) phase technique, the required superposition phase compensation of spatial propagation and OAM mode phase is realized. Additionally, a folded configuration and a reflector with gradient phase are implemented, reducing the generator profile to one-third of its original height. To further improve vortex beam propagation, a small axicon angle of 5° is introduced to mitigate beam divergence. In particular, a novel wideband planar CP magnetoelectric dipole (MED) antenna integrated with the TA metasurface is designed as the feed source. The experimental results demonstrate that the fabricated OAM generator operates over a broad frequency range from 12 to 18 GHz (40%), with the mode purity exceeding 67% (OAM mode ${l} = +1$ ). The proposed OAM generator represents a promising candidate for high-speed wireless communications.