A Transmissive Metasurface Generating Wideband OAM Vortex Beam in the Ka-Band

In this letter, a wideband transmitting metasurface is proposed to generate the orbital angular momentum (OAM) vortex beam in the Ka-band. The proposed unit cell is a novel combination of dual-square loops and a cross dipole element printed on four dielectric layers separated by an airgap. This combination of two types of elements helps to attain a linear transmission phase response with more than a 360
$^{\circ }$
phase compensation range with a transmission magnitude equal to or better than 1.1 dB. The proposed structure of the unit cell is also suitable for dual polarized applications due to its symmetrical configuration. The proposed metasurface is also fabricated and measured to verify its simulated performance. The overall measured outcome shows that the proposed structure has successfully achieved wideband performance for the OAM vortex beam with +1 mode. The overall mode purity is greater than 72% from 28.0 to 38.0 GHz, which is about 33.3% OAM bandwidth. Moreover, the peak gain of 23.8 dBi is achieved with 22.1% aperture efficiency.