Theoretical And Experimental Studies On Generation Of Vortex Electromagnetic Waves

Orbital Angular Momentum(OAM)is a physical quantity that characterizes the characteristics of electromagnetic(EM)waves in addition to intensity,phase,frequency,polarization,etc.The EM wave carrying OAM is called vortex EM wave which has helical phase distribution.Theoretically,vortex EM waves of different OAM modes are orthogonal to each other and propagate independently,which brings a new degree of freedom for EM waves.Therefore,vortex EM waves have shown important application potential in various fields and have high research value and application prospect.In recent years,microwave imaging system has been gradually applied to a variety of scenes,such as early diagnosis of breast cancer,plant root imaging,etc.If EM vortex imaging is applied to these fields,it is expected to improve the imaging resolution,and the generation of vortex EM field is the premise of its application in the imaging system.Therefore,OAM antenna array is studied in this paper,in addition,a series of work has been carried out in the aspects of OAM purity optimization,production mode,main lobe regulation and so on.The main research contents are as follows:1.In order to improve the mode purity of vortex EM wave and the resolution of EM vortex imaging,a method of vortex EM wave purity optimization based on antenna pattern control is proposed,through optimizing the scales of the array element,the differences between E-plane pattern and H-plane pattern of array element can be reduced efficiently,which results in the more uniform field intensity distributions and higher OAM mode purities.Then,the 1-D and 2-D imaging simulation of the underwater target is performed,from which it can be concluded that the higher OAM mode purity,the higher azimuth resolution.2.In order to generate high quality and high mode vortex EM field,a method for generating vortex EM fields by combine UCA is proposed.By the whole rotation of the antenna array and the phase control of each antenna element,the vortex EM waves of multiple modes can be supermposed generated.This method can not only break the spatial limitaiton of the number of array elements,but also can get higher modes of OAM with higher putity,which has great potential in the generation of high mode vortex EM waves.3.In order to apply vortex EM waves imaging to early diagnosis of breast cancer,the OAM antenna and array in oil were studied.By designing circularly polarized antenna array,vortex EM waves are generated in oil.The main lobe of the vortex EM wave is adjusted by means of adjusting the array radius,so that all the modes can irradiate the target.The imaging resolution of vortex wave has further analyzed,the relationship between the resolution and wavelength,antenna main lobe width,main lobe direction of vortex EM wave has been given.4.In order to improve the vortex imaging efficiency,a composite OAM generation method is proposed.This method can simultaneously generate two adjacent modes and control the same proportion of the two modes,the mode purity of the composite OAM can be improved by means of combine UCA proposed above.