The Research Of Microwave Correlated Imaging Methods

In the research process of radar imaging technology,high resolution has always been a very important demand.Since traditional real-aperture imaging mainly uses arrays or large-aperture antennas to generate narrow beams to obtain azimuth resolution,the range resolution is limited by the signal bandwidth,and the azimuth resolution is limited by the relative motion of the target and radar,the azimuth resolution could get the relevant information of the target through the change in the angle between the target and the radar.In actual conditions,the aperture of the array is often limited,resulting in difficult to improve its resolution,practical applications are also limited,especially in the field of long-distance imaging.Therefore,on the basis of optical correlation imaging,an incoherent temporal-space two-dimensional radiation field is constructed,and a microwave correlated imaging model is established to solve the limitation of traditional radar imaging.First of all,in this thesis,the physical process of microwave correlated imaging is analyzed in detail from the angle of electromagnetic field,and the integral model of the specific radiation field and scattering field is established,and then the integral model is discretized to get its matrix form.The performance of correlation equations to solve the target is affected by the properties of the incidence matrix.Therefore,this thesis characterizes the properties of the radiation field from the perspective of effective eigenvalues and sets a reference standard for judging the atomic correlation of the radiation field matrix.The form of the transmitted signal is one of the factors that affect the distribution of the radiation field.The use of waveforms that are independent of each other in the time domain as the transmit signal can construct as many spatially-independent radiation field samples as possible,thereby increasing the randomness of the radiation field.Secondly,after the radiation field and the scattered field are obtained,the target scattering coefficient is obtained by correlating the radiation field formed by the space with the scattered field.This thesis compares the inversion of imaging results under different noise conditions by different solving algorithms,including direct association algorithm,pseudo-inverse algorithm,truncated singular value decomposition algorithm,Tikhonov regularization algorithm,and sparse reconstruction algorithm.However,the inversion result of the above correlation processing algorithm is not ideal.Therefore,this thesis improves the total variation regularization algorithm.After considering the actual situation,constraints such as real number constraints,non-negative constraints,and amplitude and phase resolution are added.This makes the prior information of the target fully utilized.At the same time,the Augmented Lagrange Multiplier Method was used to prevent the occurrence of penalties that tend to be infinite.In addition,the improved total variation regularization is further sparsely constrained for targets with sparseness.At the same time,due to the increase of some constraint variables in the solution process,the number of unknowns increases,so for the solution of multiple unknowns,an alternating direction method of multipliers algorithm is used in this thesis.This chapter optimizes the correlation algorithm,improves the imaging quality after inversion of the target,achieves high-quality imaging under noise interference conditions,and compares and analyzes the results.Finally,the error of the radiation field will be caused by the error of off-grid problem and the position error of the array element in the actual microwave correlated imaging process,which is mismatched with the scattering echo.On this basis,the proposed model with errors is improved.Taylor expansion is used to represent the actual incidence matrix as the deduced correlation matrix plus its error matrix.The alternating direction method of multipliers algorithm is used to optimize and solve the radiation field error matrix and the target scattering coefficient,and the results are analyzed.