1. Djordjevic, I. B., "Multidimensional OAM-based secure high-speed wireless communications," IEEE Access, Vol. 5, 16416-16428, 2017.
2. Mao, F. C., M. Huang, C. F. Yang, T. H. Li, J. L. Zhang, and S. Y. Chen, "Orbital angular momentum generation using circular ring resonators in radio frequency," Chinese Phys. Lett., Vol. 35, No. 2, 020701, 2018.
3. Ren, Y. X., Z. Wang, P. C. Liao, L. Li, G. D. Xie, H. Huang, Z. Zhao, Y. Yan, N. Ahmed, A. Willner, M. P. J. Lavery, N. Ashrafi, S. Ashrafi, R. Bock, M. Tur, I. B. Djordjevic, M. A. Neifeld, and A. E. Willner, "Experimental characterization of a 400 Gbit/s orbital angular momentum multiplexed free-space optical link over 120 m," Opt. Lett., Vol. 41, No. 3, 622-625, 2016.
4. Yan, Y., G. D. Xie, M. P. J. Lavery, H. Huang, N. Ahmed, C. J. Bao, Y. X. Ren, Y. W. Gao, L. Li, Z. Zhao, A. F. Molisch, M. Tur, M. J. Padgett, and A. E. Willner, "High-capacity millimeter-wave communications with orbital angular momentum multiplexing," Nat. Commun., Vol. 5, 4876, 2014.
5. Shi, Y. and Y. Zhang, "Generation of wideband tunable orbital angular momentum vortex waves using graphene metamaterial reflectarray," IEEE Access, Vol. 6, 5341-5347, 2018.
6. Tamburini, F., E. Mari, G. Parisi, F. Spinello, M. Oldoni, R. A. Ravanelli, P. Coassini, C. G. Someda, B. Thidé, and F. Romanato, "Tripling the capacity of a point-to-point radio link by using electromagnetic vortices," Radio Sci., Vol. 50, No. 6, 501-508, 2015.
7. Yu, S. X., L. Li, G. M. Shi, C. Zhu, and Y. Shi, "Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain," Appl. Phys. Lett., Vol. 108, No. 24, 241901, 2016.
8. Mao, F., M. Huang, T. Li, J. Zhang, and C. Yang, "Broadband generation of orbital angular momentum carrying beams in RF regimes," Progress In Electromagnetics Research, Vol. 160, 19-27, 2017.
9. Yu, S. X., L. Li, G. M. Shi, C. Zhu, X. X. Zhou, and Y. Shi, "Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain," Appl. Phys. Lett., Vol. 108, No. 12, 121903, 2016.
10. Edfors, O. and A. J. Johansson, "Is orbital angular momentum (OAM) based radio communication an unexploited area?," IEEE Trans. Antenn. Propag., Vol. 60, No. 2, 1126-1131, 2012.
11. Cagliero, A. and R. Gaffoglio, "On the spectral efficiency limits of an OAM-based multiplexing scheme," IEEE Antenn. Wirel. Pr., Vol. 16, 900-903, 2016.
12. Cheng, W. C., H. L. Zhang, L. P. Liang, H. Y. Jing, and Z. Li, "Orbital-angular-momentum embedded massive MIMO: Achieving multiplicative spectrum-efficiency for mmWave communications," IEEE Access, Vol. 6, 2732-2745, 2017.
13. Zheng, S. L., R. F. Dong, Z. F. Zhang, X. B. Yu, X. F. Jin, H. Chi, Z. N. Chen, and X. M. Zhang, "Non-line-of-sight channel performance of plane spiral orbital angular momentum MIMO systems," IEEE Access, Vol. 5, 25377, 2017.
14. Zhu, Q. B., 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, 2456, 2015.
15. Lei, W., F. Jiang, Z. Yuan, J. Yang, G. Gui, and H. Sari, "Mode division multiple access: A new scheme based on orbital angular momentum in millimeter wave communications for fifth generation," IET Commun., Vol. 12, No. 12, 1416-1421, 2018.
16. Chen, R., H. Xu, M. Moretti, and J. D. Li, "Beam steering for the misalignment in UCA-based OAM communication systems," IEEE Wirel. Commun. Lett., Vol. 7, No. 4, 582585, 2018.
17. Opare, K., Y. Kuang, and J. Kponyo, "Mode combination in an ideal wireless OAM-MIMO multiplexing system," IEEE Wirel. Commun. Lett., Vol. 4, No. 4, 449-452, 2015.
18. Zhao, L. J., H. L. Zhang, and W. C. Cheng, "Fractal uniform circular arrays based multi-orbital-angular-momentum-mode multiplexing vortex radio MIMO," China Commun., Vol. 15, No. 9, 126-143, 2018.
19. Wang, L., X. H. Ge, R. Zi, and C. X. Wang, "Capacity analysis of orbital angular momentum wireless channels," IEEE Access, Vol. 5, 23069-23077, 2017.
20. Ge, X. H., R. Zi, X. S. Xiong, Q. Li, and L. Wang, "Millimeter wave communications with OAM-SM scheme for future mobile networks," IEEE J. Sel. Area. Comm., Vol. 35, No. 9, 2163-2177, 2017.