Free-Space Radio Communication Employing OAM Multiplexing Based on Rotman Lens

The design of a radio communication system employing orbital angular momentum (OAM) mode multiplexing is described. Rotman lenses followed by circular antenna arrays are used to transmit and receive radio frequency beams carrying OAM. In our experiment, two 3 × 3 Rotman lenses are fabricated to feed the three-element circular arrays with certain phase gradients for OAM modes multiplexing and demultiplexing. The OAM-carrying beams of mode number l = +1, 0, and -1 are generated at 9.7 GHz, with each channel carrying an independent data stream of 40 Mbit s
^-1
quadrature phase shift keying signal in a bandwidth of 20 MHz. And all three channels are recovered with bit error rates below the forward error correction limit of 3.8 × 10
^-3
.