Design Of The Novel Vortex-Beam Antenna Based On The Theory Of Characteristic Mode

This thesis studies how to design orbital angular momentum(OAM)antennas by combining the analytical models and the characteristic mode.Mode theory is quite popular in the field of microwave and antenna engineering.Only by deeply understanding the various mode theory in electromagnetic field can we better deal with various problems arise from the microwave and antenna engineering.There are two kinds of antennas in the view of working mechanism: traveling wave antenna and standing wave antenna.Traveling wave antenna guides the traveling wave while radiating at the same time,thus causing low radiation efficiency;The physical essence of standing wave antenna is external resonance,while the characteristic mode is just the mode theory related to such resonance.Characteristic mode have been widely used in antenna engineering recently because of its clear physical background and superior mathematical properties that it can be used as global basis functions and its orthogonality in nature.Characteristic modes can provide more physical and essential explanations for antennas operating in the resonant state,thus helping people better understand the working mechanism of resonant antennas.On the other hand,the research of beams with OAM property has extended from optical band to microwave band in recent years.Owing to the special phase wavefront and the orthogonality of its modes,OAM beams have great application prospects.They can be used in imaging,target detection,near-field sensing and communication and so on,the OAM is a hot spot in the field of microwave and antenna engineering now.The purpose of this paper is to design the OAM antenna based on the theory of characteristic mode to show the value of characteristic mode in the field of OAM antenna designing.Firstly,the existing microwave band OAM generation methods are classified into four kinds of analytical models as the pre-work,and then based on the analytical models,it is pointed out how to extract the topology charge number of the orbital angular momentum beams with circular polarization.Then a series of antenna design work is done by using the work flow: building analytical models?current fitting of the analytical models using characteristic mode and full-wave verification.The final achievements include:Yagi-type metal-ring OAM antenna,octagonal microstrip patch OAM antenna and parallel magneto-electric dipole OAM antenna.The physical property of the superposition of the OAM mode number of the antenna element and the array is also verified by simulation and experiment by using the octagonal patch antenna array.All these antennas mentioned above possess both spin orbital angular momentum(SAM)and OAM properties,so they can be named all-angular momentum(AAM)antenna to characterize their rich electromagnetic diversity.The radiation field of the AAM antennas has the characteristics of both vector and scalar vortices in spatial distribution,so the AAM antennas have considerable potential application value(e.g.communication and imaging).In the process of designing these antennas,the ideas of concept extension,mode splicing and mode modification are used throughout.It is believed that these ideas can be naturally extended to other types of antenna designs with complex modes.