1. [1] B. Thidé, H. Then, J. Sjöholm, K. Palmer, J. Bergman, T.D. Carozzi, Y.N. Istomin, N.H. Ibragimov, and R. Khamitova, “Utilization of photon orbital angular momentum in the low-frequency radio domain,” Phys. Rev. Lett., vol.99, no.8, 087701, 2007. 10.1103/physrevlett.99.087701
2. [2] Q.B. Zhu, T. Jiang, D.M. Qu, D. Chen, and N.R. Zhou, “Radio vortex multiple-input multiple-output communication systems with high capacity,” IEEE Access, vol.3, pp.2456-2464, Nov. 2015. 10.1109/access.2015.2503293
3. [3] D.L. Andrews and M. Babiker, The Angular Momentum of Light, Cambridge University Press, New York, 2013. 10.1017/CBO9780511795213
4. [4] J.D. Jackson, Classical Electrodynamics, 3rd ed., Wiley, 1999.
5. [5] C. Zhang, J. Jiang, and Y.F. Zhao, “Euclidean space with orbital angular momentum,” Workshop on EM Wave Transmission with OAM, IEEE International Conference on Communications, Shanghai, China, May 2019. 10.1109/iccw.2019.8756875