Reconfigurable OAM Antenna With Flexibility on Mode Numbers, Polarization, and Frequency

As existing orbital angular momentum (OAM) antennas have no control on the operating frequency after fabrication and cannot simultaneously manipulate the polarization and mode number, designing smart OAM wireless communication systems are out of reach. However, in this letter, a new OAM antenna system is proposed that can efficiently overcome the aforementioned limitations. The suggested antenna utilizes a 2 × 2 uniform circular array (UCA) composed of multiple-input–multiple-output (MIMO) antennas to introduce the MIMO-UCA technique for simultaneous generation of OAM mode numbers +1 and −1. The flexibility on polarization of each mode stems from the fact that each MIMO antenna consists $\pm {\text{45}}^{\circ }$ polarized elements, thus utilization of tunable feeds assigns the modes to the desired polarization simultaneously. The flexibility on the operating frequency is due to the frequency-reconfigurability of MIMO antennas as well. The fabricated prototype of the proposed structure verifies the simulated results. The operating frequency can be tuned from 3.8 to 4.4 GHz. Over this band, the maximum gain is preserved above 6 dBi. The mutual coupling between the ports is below −20 dB.