Ultra Narrow Band Transmission System with Orbital Angular Momentum

Abstract

Usually, the electromagnetic wave will occupy the bandwidth in the frequency domain in the process of the information transmission. The spectrum is important resource in the information transmission just like the space and time. How to use the limited spectrum is a significant issue in the field of communications. Ultra Narrow Band (UNB) transmission system with Orbital Angular Momentum (OAM) can directly carry the data through the dimension of OAM, which builds the communications system without or less occupying the traditional resource of the frequency domain. As an OAM microwave photon generator, gyrotron can produce OAM photon with different modes. After the photon carrying OAM passes through the diffractive metal film, it will produce corresponding diffraction patterns with different modes. The modes of photon can be detected according to the patterns. However, the traditional antenna can detect carrier waves with Electric Field Strength rather than detect OAM modes. So the bandwidth of transmission signal is expected to be very small if the continuously changing phases are detected. In fact, when different modes of the transmitter are switched, the phase of the single frequency carrier signal can not be completely synchronized, and the bandwidth will expand. At this time, the system will become a UNB system. In this paper, the UNB transmission system based on OAM microwave photon is studied. The influence of the different transmitter phase on the spectrum and power spectrum is analysed. At the same time, the channel capacity is given.