Mode Purity Analysis of an Orbital Angular Momentum Antenna

Orbital Angular Momentum (OAM) beams with a different topological charge are orthogonal to each other and hence can be multiplexed together on the same frequency. There are many techniques by which the OAM beams are being generated. However, the generated OAM beams are not always pure in nature which can influence the orthogonal nature of the OAM waves, and the cross-talk between adjacent modes may happen. So, it is very important to perform the mode purity analysis while designing the OAM antenna. This paper describes the mode purity analysis of the four-element Uniform Circular Array (UCA) generating first-order OAM beams. The UCA consists of circular patch antennas operating at 10 GHz. By properly exciting each antenna element with the corresponding phase values, the first order OAM beams with l = ±1 modes are generated. The mode purity analysis of the generated OAM beams is performed by the spectral analysis of the Fourier transform of its azimuth angular distribution. The variation of the mode purity with the sampling circle radius and with the transmission distance has been studied.