Near Field OAM And The Robustness Of Deflection And Rotation Of OAM System Using Multi-port-fed Antenna

In the paper, we study the near field Orbital Angular Momentum (OAM) using the rigorous numerical methods. We derive the rigorous field channel matrix for near field transmitting/receiving system. Then using the numerical method-Multi-Level Green’s Function Interpolation Method (MLGFIM) to calculate the admittance matrix of the system, from which we can futher obtain the demodulation performance of OAM. At the same time, the method can also calculate the field performance of OAM, and the results are compared with those obtained by commercial software-CST MWS. Meanwhile, we figure out the error when we utilize the far field channel matrix in the near field OAM system.Futhermore, we design a multi-port-fed loop antenna, and theoretically prove that it can generate OAM, as the main mode exist the phase item:eilφ. Then we rotate the loop antenna, and find it has rotate robustness. At the same time, we study the correction technology when the receive antenna is not at the center of transmitting beam axis. We derive the correction factor under the circumstances, and prove the correctness of the factor based on the numerical results, which we define the modes purity.At last, as the feed networks are extremely complex, here we do not figure them out. For further research, we add a ground not only just as a reflector, but as a separator to isolate the anteena and the feed networks, so that the networks can be studied inpendently. In the paper, we describe the performaces of the communication system with ground.