Study On The Generation Method Of Multi-Mode Vortex Electromagnetic Wave

The electromagnetic spectrum has the features of finiteness,exclusiveness,non-exhaustion and being polluted easily.Therefore,improving the spectrum efficiency is one of the driving forces to solve the development of information technology.At present,the electromagnetic wave carrying information is controlled by changing the polarization,frequency,and amplitude.As a new dimension,orbital angular momentum(OAM)has a great potential for the application of improving the spectrum resources utilization and radar imaging resolution.This thesis mainly study the generation method,based on the circular antenna array and metasurface,of the vortex electromagnetic wave carrying OAM.Firstly,the theoretical derivation about circular antenna array generating the vortex electromagnetic wave is carried out.Both theoretical derivation and array's OAM state are compared with each other,which proves the accuracy of the formula reasoning.We propose the antenna array composed of the antenna unit carrying OAM.Both theoretical formulas and simulation results have proved that the array's OAM state is not only related with the array's parameter,but also with the unit carrrying OAM.Hence,in theory,the unit's flexible OAM state adjustment would change the array's total OAM state at a low cost.Meanwhile,antenna array's OAM state would be extended by the unit,which couldn't be limited by the unit number.Furthermore,based on the new antenna array composed of the OAM unit,we propose an idea for improving the new antenna array's OAM state purity,which gives a thought for the application of the new antenna array in the future.Then,based on the theory about circular antenna array,we propose a dual-band and dual-state antenna array composed of 8 units to generate the vortex electromagnetic wave.The dual-band microstrip antenna unit and dual-band differential phase feeding network are designed for working at 0.9GHz and 1.8GHz,then combining the unit and feeding network to generate the array.At 0.9 GHz,the phase difference between every unit is 45°,which would generate the vortex electromagnetic wave with OAM state 1.Moreover,at 1.8GHz,the phase difference between every unit is 90°,which would generate the vortex electromagnetic wave with OAM state 2.The OAM state about the designed antenna array is researched,which coincides with the simulation phase results.Concerning the above designed array,we have fabricated and tested it,whose measured radiation patterns are basically same with the theoretical results.Finally,an OAM generator based on electromagnetic meatsurface is proposed.The Pancharatnam-Berry element is used to construct the metasurface.By rotating the unit with certain angles,the transmission phase or reflection phase of electromagnetic wave would be regulated.At 10 GHz,the metasurface antenna would generate the transmitted vortex electromagnetic wave with OAM state of-1 and LHCP,meanwhile the reflected vortex electromagnetic wave with OAM state of 1 and RHCP.It is the first time that the metasurface array simultaneously regulates the polarization,direction and OAM state,which proposes a path for the multidimensional regulation of the vortex electromagnetic wave.In this thesis,based on the circular antenna array and metasurface,we systematically studied the method for generating OAM,which further enriches the current method of generating OAM.