Study On Detection And Imaging Of High-speed Moving Targets With Wideband Radar

Nowadays,national defense is more and more threatened by high-speed weapons,such as ballistic missiles,unmanned reconnaissance aircraft and so on.How to enhance the ability in detection,tracking,imaging and recognizing of high-speed moving targets already became the frontier topic and the urgent task in the field of radar technology.With the advantage of high range resolution,wideband radar echo can offer more information about the targets,including the presence,location,and characteristics of the targets.By enhancing the signal bandwidth,the one-dimensional range profile and range-Doppler imaging can be obtained,the ability in target detection and the accuracy of target parameters estimation can also be improved.However,the range migration caused by targets' high speed would result in the decrease in the resolution and signal-to-noise(SNR)of conventional radar signal processing.Due to the range migration,the coherent integration cannot be effectively done,the broadening in one dimensional range profile and obscure in range-Doppler image may also be caused.Therefore,how to accomplish the task of target detection,tracking,imaging and identification by the coherent integration of the wideband radar echo has become an attractive issue in the field of radar signal processing.The detection and imaging processing of high-speed target is studied in this dissertation,with emphasis on the target model in wideband radar,coherent integration,velocity and LFM parameter estimation,and ISAR imaging.The main contents and results of this dissertation can be summarized as follows:1.The characteristics of high-speed moving targets' echo in narrowband radar and wideband radar are extracted.In order to improve the detection performance of high-speed moving targets,the target model is given and the characteristics of echo are studied.The principle of moving targets' range migration and the affect in coherent integration are studied.The impacts of high-speed movement in narrowband and wideband radar echo are also analyzed.Compared with narrowband radar,target echo in wideband radar can no longer be regarded as a point target,but an extended target in range.The scattering centers in the extended target can be treated as a collection of several point targets.The ranging error and spectrum broadening in wideband radar caused by targets' high-speed movement are analyzed and simulated.2.A range migration correction method based on the velocity spectrum is proposed.The effect of coherent integration after range migration correction is simulated and analyzed.The principle of coherent integration is studied.The phenomenon of range migration caused by high-speed movement is simulated.In the case of narrowband and wideband radar,the coherent integration based on the velocity spectrum method is simulated.The results show that,the proposed range migration correction method based on the velocity spectrum is more suitable for wideband radar.The Keystone transform and the application of Keystone in range migration correction are also studied and simulated.The results show that,the coherent integration after Keystone transform can obtain better performance,including the increase in integration gain and avoiding the spectral broadening.3.An improved range profile cross-correlation method for velocity estimation based on the cross-power spectrum is proposed.Against the limitation of integer rang bin in the conventional cross-correlation method,the improved method based on the fractional delay estimation is given.With the more accurate location estimation of the cross-correlation peak,the accuracy of velocity estimation can be improved.The conventional cross-correlation method and the improved method are simulated and analyzed.4.A phase fitting method for velocity estimation based on the phase of target echo is proposed.In the condition of very high-speed,the expansion effect can no longer be ignored.Considering the expansion effect,the phase fitting method based on the wideband stretch processing is given.The method of phase unwrap is also be studied.The simulation and analysis show the effectiveness of the proposed method.5.The LFM parameter estimation methods based on joint time-frequency analysis are studied.Wigner-Hough transform and Fractional Fourier transform are discussed in detail.The relationship between the two methods is also studied.The LFM parameter estimation method based on Fractional Fourier transform are simulated and analyzed.6.A rang alignment method based on fractional delay filter for ISAR motion compensation is proposed.For traditional range alignment methods,with the limitation of integer range bins,the maximum alignment error can be up to half a range bin.In the proposed method,with the fractional delay estimation and fractional delay filter,the accuracy of range alignment for ISAR can be improved.Therefore,better range alignment would result in better performance in focus quality of ISAR images.The proposed method is also verified by the real ISAR data.