Generation,Reception Of Electromagnetic Vortex And Its Applications In Imaging

Orbital angular momentum is a new degree of freedom of electromagnetic wave.Different orbital angular momentum modes constitute orthogonal basis in infinite dimensional space,which has the potential capability of multiplexing and solves the problem of electromagnetic spectrum congestion by improving spectrum efficiency.The amplitude of electromagnetic vortex has a term of the first type of Bessel function and the illumination on the imaging area has a varying amplitude weighting,which may break through the antenna aperture to realize the super-resolution imaging within the antenna footprint.This thesis provides error analysis of generation and reception of the electromagnetic vortex based on uniform circular array,the error threshold is obtained when orbital angular momentum mode can be accurately distinguished,and concludes the receiving conditions of orbital angular momentum,which will provide technical reference for the generation and reception of eletromagnetic vortex.This thesis also explores and evaluates the potential of application in radar detection and imaging with electromagnetic vortex.The thesis first analyses the impact on the amplitude and phase characteristics of eletromagetic vortex when excitation amplitude or phase errors of array element exist,such as Gaussian distribution error,the quantization error,the single array error,the number elements and so on.The phase gradient method is applied to calculate the orbit angular momentum mode and gives the error threshold under which the mode can be accurately identified.The simulation results show that the main lobe of the electromagnetic vortex becomes irregular ring shape under various excitation amplitude and phase error.The phase is well maintained in the main lobe and deteriorates at the center and edge region where the amplitude intensity is very low.The conclusion is that the electromagnetic vortex has good anti-interference characteristics with respect to the excitation amplitude and phase error.The error analysis of the receiving scheme based on uniform circular array has been carried out.The amplitude and phase change of eletromagetic vortex has been simulated when the receiving array is not parallel to the transmitting array,namely there is a tilt-angle.The results signify that electromagnetic vortex has a strong sensitivity to the inclination angle error between receiving array and transmitting array.Even when the angle is 3 degrees,orbital angular momentum mode cannot be distinguished by the phase distribution.In addition,the receiving and detection conditions of basic receiving schemes are clarified.Finally,the application of electromagnetic vortex in radar detection and imaging is investigated.According to the amplitude hollow feature of electromagnetic vortex,the side-view imaging system is chosen,the imaging model is established,and the least squares algorithm is applied to retrieve the image.The simulation results indicate that the resolution of electromagnetic vortex can be improved 1.8 times compared with the traditional signal with the same parameters.Then the imaging results of electromagnetic vortex are assessed.Due to the circular symmetry and the hollow structure of electromagnetic vortex,the super-resolution imaging capability is limited.The condition number of imaging matrix for electromagnetic vortex illumination is rather high.With the increase of signal to noise ratio,the reconstruction image can identified and the root mean square error can be reduced,and the magnitude of the improvement can ameliorate to some extent.