Generation of OAM Radio Waves Using Circular Vivaldi Antenna Array

This paper gives a feasible and simple solution of generating OAM-carrying radio beams. Eight Vivaldi antenna elements connect sequentially and fold into a hollow cylinder. The circular Vivaldi antenna array is fed with unit amplitude but with a successive phase difference from element to element. By changing the phase difference at the steps of 0, +/- 45 degrees, +/- 90 degrees, +/- 135 degrees, and 180 degrees, the OAM radio beam can be generated with mode numbers 0, +/- 1, +/- 2, +/- 3, and 4. Simulations show that the OAM states of +/- 2 and +/- 3 are the same as the traditional states, while the OAM states of 0, +/- 1, and 4 differ at the boresight. This phenomenon can be explained by the radiation pattern difference between Vivaldi antenna and tripole antenna. A solution of distinguishing OAM states is also proposed. The mode number of OAM can be distinguished with only 2 receivers.