Communication Between Rectangular Phased Arrays on an Orbital-Angular-Momentum-Encoded Link

We demonstrate a point-to-point orbital angular momentum (OAM) free-space radio frequency link at 26.5 GHz in an indoor far-field anechoic chamber. OAM modes <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\ell=\pm 1$</tex> are generated by a rectangular phased array antenna and transmitted to a similar array for detection. This is done in contrast to much of the existing work on utilizing OAM to increase communication link capacity, which have tended to focus on the use of purpose-built uniform circular arrays [1]–[5]. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Es/No$</tex> is measured for several configurations of the transmitter and receiver pair to estimate modal crosstalk and baseline performance, and a study on how link performance is impacted by phase precision is described. We find that readily available rectangular phased array antennas can exhibit sufficient performance - suppression in excess of 20 dB for undesired modes - to warrant consideration for nearer-term implementation of OAM multiplexing into the telecommunications infrastructure.