An OAM Patch Antenna Design and Its Array for Higher Order OAM Mode Generation

In this letter, a systematic design procedure is proposed on how to implement the characteristic mode analysis to design and optimize an orbital angular momentum (OAM) antenna with circular polarization. The main idea of this work is by combining proper high-order modes to fit the current distribution of the analytical model. It is shown that by using proper high-order modes, a single antenna element could act like an array making the antenna system more compact. As a prototype, a patch antenna working at the 2.4 GHz Wi-Fi bands to generate the right-hand circularly polarized OAM beam with topology charge l_OAM = -1 is designed, fabricated, and measured to demonstrate the design method. In addition, an array composed by the proposed antenna element is designed and experimented. New physical phenomenon is found that the OAM modes of the antenna element and the array can be combined considering the multiplication theorem. The combination relaxes the restriction of |l_OAM| <; N/2 to some extent in comparison with the traditional uniform circular arrays for OAM generation.