| With the advent of big data era and the rapid development of Internet of Things,people's demand for wireless communication rate increased rapidly.In the past few decades,in order to improve the rate of wireless communication,a number of technology has been proposed and developed,such as polarization multiplexing,orthogonal frequency division multiplexing(OFDM)and so on.Therefore,how to further improve the spectrum utilization is a tough problem.The vortex electromagnetic wave which based on orbital angular momentum multiplexing can improve the spectrum utilization and increase the capacity of the channel,so it becomes a research hotspot in the field of electromagnetism and communication.In this paper,based on orbital angular momentum and vortex electromagnetic wave,the vortex electromagnetic wave communication system and the vortex electromagnetic wave antenna are mainly studied.The main contents are divided into five parts shown as follows.Firstly,the research background,significance and current research status of this subject are introduced.Then the development of vortex wave is reviewed and the main work,content arrangement and main innovation point of this paper are summarized.Secondly,the basic theory of orbital angular momentum and vortex electromagnetic wave is summarized.The detailed derivation process is given and the physical meaning is fully explained.On the basis of the above work,this paper introduces the various components of the wireless communication system in detail,including the generation,propagation and demodulation of the vortex electromagnetic wave.In this paper,the generation of electromagnetic vortex wave and the method of receiving and demodulating are described extensively,and the problems encountered in the vortex electromagnetic wave generation,propagation,reception and demodulation are analyzed.Thirdly,based on the single circularly polarized circular patch,a novel multimode circularly polarized patch antenna is proposed in this paper.The proposed antenna consists of three concentric patches on the same substrate,one circular patch and two shorted annular ring patches.The central circular patch excites the dominant TM11 mode with circular polarization.In addition,the two outer shorted annular ring patch excites the TM21 and TM31 higher order mode with circular polarization,respectively.This antenna is analyzed theoretically in detail and the mathematical expression of the electric field of the circular polarized patch antenna is given.For circularly polarized patch antenna with TMnm mode,which can produce n-1 order OAM mode electromagnetic vortex wave,so the multimode circularly polarized patch antenna can generate three orbital angular momentum model at the same time.Besides,some other OAM states can also be achieved by changing the circular polarization rotation of patches.The simulation and experimental results of the proposed multimode circularly polarized vortex wave antenna are given.Fourthly,the holographic artificial impedance surface is innovatively used to generate electromagnetic vortex wave.This paper designed a holographic vortex electromagnetic wave holographic antenna based on holographic artificial impedance modulation.It is the first time that the holographic artificial impedance surface is used to control the orbital angular momentum.The basic principle of microwave holography and holographic artificial impedance surface are systematically introduced.The design process of holographic artificial impedance surface is given.At the same time,the holographic vortex electromagnetic wave antenna with l = 1 OAM mode is taken as an example,the detailed design process and simulation results are given.It can be concluded that the holographic tensor artificial impedance surface can be used to control orbital angular momentum.Finally,the research of this paper is summarized and the future study plan is proposed. |
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