Research Of Generation Of Vortex Beam Based On Field Transformation

The method of generation of electromagnetic vortex beam with orbital angular momentum(OAM)has been a research hotspot in recent years.Since the orbital angular momentum introduces a new degree of freedom and can theoretically have an infinite number of modes orthogonal to each other,it is possible to further improve the capacity and spectrum efficiency of communication systems thus being very valuable of research.In order to generate vortex beam with the compact structure antenna,three novel methods are proposed in this paper:1.Based on the theory of complex transformation optics,the parameters of the substrate under the circular patch are changed and a standing-wave current distribution along the circumference of a conventional circular patch is transformed into a uniform traveling current distribution instead,thus leading to the generation of vortex beams.At different frequencies,the conventional circular patch antenna can respectively excite three modes of electromagnetic waves of TM11,TM21,TM31,so that the antenna after coordinate transformation can correspondingly excite the first-order,second-order and third-order vortex beam.2.Design a concentric circular patch antenna that can excite three modes of electromagnetic waves of TM11,TM21,TM31,on the three patches separately at 5GHz through the control of feeding mode.Three different complex coordinate transformations are applied to three patches,resulting in the generation of the first-order,second-order and third-order vortex beam at the same frequency of the same antenna.3.According to the characteristic modes analysis of the circular patch antenna,the circular patch has the surface current distribution which is orthogonal to each other.Therefore,the vortex beam can be generated on the circular patch by adding an appropriate feeding network.The six L-probes are fed in different phases at different positions under the circular patch.Then the first and second order vortex beam can be excited at 2.3 GHz respectively,and the antenna can be optimized by loading the short pins.Through the combination of transform optics,the theory of characteristic modes and the antenna design,it will provide new ideas for antenna design and produce more innovations and achievements.