A study on the near field OAM using the rigorous numerical methods

In this paper, we investigate the near field Orbital Angular Momentum (OAM) using the rigorous numerical methods. To model the communication channel of the OAM system, we derived a rigorous channel matrix for the near field transmitter/receiver system. This channel matrix is composed of the admittance matrices of the system. To obtain these admittance matrices, the integral equation method is employed. We also use Multilevel Green's Function Interpolation Method (MLGFIM) in accelerating the matrix-vector multiplications while solving the integral equations iteratively. Comparing with the far field channel matrix used in conventional communications that omits the feedback effects, the near field channel matrix rigorously takes into account the multiple coupling between the transmitter and the receiver.