Four-value multiplexing orbital angular momentum communication scheme using loop antenna arrays

A four-value multiplexing orbital angular momentum (OAM) communication scheme is demonstrated using loop antenna arrays. Considering the radiated fields of loop antennas, MIMO communication without signal processing is shown to be realized by controlling the current distribution in a single Fourier expansion coefficient. Through numerical analysis on the current, a single coefficient is shown to be dominant, where the loop perimeter is approximately the integral multiple of the wavelength. For long-range OAM communication, diffraction patterns of the collimated fields with paraboloids are analyzed, and the diffraction is shown to have a greater effect on the higher OAM modes. For short-range communication, four-element loop antenna arrays are estimated by simulations and measurements. The transmission coefficient between the antennas of the same perimeter is shown to be larger by more than 12 dB than those of a different perimeter for a 1-cm distance. For long-range communication, a collimating configuration is proposed, and the transmission coefficient between the antennas of the same perimeter is shown to be larger by more than 11 dB for a 1-m distance.