Research On The Impact Of Group Delay On UWB LFM Radar And Its Estimation And Correction Method

In recent years,with the increasing bandwidth of imaging radar,the impact of group delay distortion on the whole radar system will also become more and more serious.How to estimate and compensate the group delay distortion of radar system especially the ultra-wideband radar which has developed rapidly in recent years accurately,has always been an important research direction in the field of radar imaging.Because the traditional estimation and correction methods of group delay distortion have some limitations in UWB LFM system,this paper studies the estimation and correction methods of group delay distortion for UWB LFM radar.The main contents of this paper are as follows:Firstly,the influence of group delay distortion on the demodulated differential frequency signal in UWB system is analyzed.The nonlinear phase polynomial is used instead of Taylor expansion to express the nonlinearity of the differential frequency signal,and the nonlinear phase model of group delay distortion in UWB linear frequency modulation system is determined.The analysis results show that the second-order and third-order nonlinear phase terms are the main factors that cause the range profile distortion of UWB LFM radar in practical engineering.Secondly,the group delay distortion estimation method based on higher-order ambiguity function is studied.The differential frequency signal of a strong scattering point whose distance is known is used as the estimated signal.As the signal is a typical non-linear phase signal,the parameters of the non-linear phase polynomial are estimated by using higher-order ambiguity function.In view of the possible lack of strong scattering points with known distances in practical engineering,the correct target location is searched by iteration of information entropy,and the group delay distortion is estimated.Finally,the shortcomings of traditional complex method in group delay distortion correction are analyzed.A group delay distortion compensation method based on Fourier transform is studied.Through multiplying the estimated group delay distortion nonlinear phase polynomial signal with a linear frequency modulation reference signal,the nonlinear phase is transformed into a unified form independent of the different target time delay by correlated signal processing.The group delay distortion correction of target echoes with different distances can be accomplished by a unified correction process,which overcomes the disadvantage of traditional methods that can not correct target images with different distances at the same time.The calculation efficiency of the algorithm is very high,and it has good engineering practical significance.