Research On Radiation Mechanism Of Radio Frequency Vortex Electromagnetic Wave

Electromagnetic orbital angular momentum(Orbital Angular Momentum,OAM)has been a research hotspot in the field of electromagnetic fields in recent years.The reason is that it may become a new dimension of information modulation,greatly expanding the ability of electromagnetic waves to carry and transmit information.Over the past three decades,OAM has received extensive research and discussion in both the optical and microwave fields.The electromagnetic wave carrying OAM has a spiral transverse phase structure,so it is also called vortex electromagnetic wave or vortex wave.Because vortex electromagnetic waves of different topological charges are strictly orthogonal to each other,these vortex waves can propagate independently in space without disturbing each other.In theory,vortex waves of different modes can form independent channels or independent observations.This feature provides great prospects for its application in the field of communications or radar.In order to apply vortex electromagnetic waves to a wider range of physical systems,we should systematically study three aspects,vortex wave radiation,propagation and reception.This article will systematically sort out and study the radiation problem of vortex waves and provide solutions for vortex wave generation.This paper first summarizes the currently known vortex wave radiation schemes.The widespread methods include:spiral reflection structure(open parabolic antenna),spiral transmission structure(spiral phase plate),higher-order mode radiation(microstrip higher-order mode)and circular antenna array.All the current vortex wave radiation structure can be attributed to the above four schemes,or its deformation.Introducing proper phase difference is its core idea.Based on the previous work,the problems of vortex wave radiation system solved in this paper include that the system is complex,the bandwidth is limited,the profile is too high,and the mode is single.In different application scenarios,the priority of these problems is obviously different,but all of them restrict the application scope of the OAM system.Therefore,providing solutions to the above problems can further expand the application field of the OAM system.The main research contents of the paper are summarized as follows:First,a circular antenna array without phase shift is designed to radiate vortex electromagnetic waves.First,the detailed of the working principle of the traditional vortex electromagnetic wave circular antenna array is analyzed.On this basis,the working principle of radiating electromagnetic vortex waves of the circular antenna array without phase shift is deduced,and the typical characteristics of the circular antenna array without phase shift are summarized.Finally,based on the traditional microstrip circularly polarized antenna,the antenna array samples are designed and manufactured for simulation and experimental verification.Second,it mainly introduces the coupling method between the spin angular momentum and the orbital angular momentum of broadband electromagnetic waves.First,the physical mechanism and conditions of coupling between spin angular momentum and orbital angular momentum are introduced.Then,designing the metamaterial unit that meets the above conditions,and extract its equivalent circuit structure,analyze its frequency response and broadband characteristics,and summarize the optimization methods and design rules.Finally,process the experimental samples and compare the simulation with the experimental results.Third,introduce the vortex electromagnetic wave antenna based on the impedance modulation surface.First,the working principle of the impedance modulated surface antenna is introduced.Secondly,designing the impedance distribution required to receive radiated electromagnetic vortex waves,and then realizing the above impedance distribution through the metal slot structure.Finally,simulation verification is carried out.Fourth,introduce the multi-mode electromagnetic vortex wave radiation method.First,the method of radiation field based on metasurface is introduced.Then it introduces the electromagnetic vortex wave radiation scheme of multi-mode and multi-beam based on harmonic expansion method,random interleaving method and other schemes.Secondly,OAM mode dispersion is analyzed under off-axis transmission and multi-path transmission situation.Finally,the single beam multi-mode hybrid electromagnetic vortex wave radiation scheme is introduced.The relevant design theories and methods are verified through sample processing and experimental testing.