Radar Three Dimensional Imaging Techniques Of Targets

Three-dimensional imaging of radar has important application perspective in the fields of precise navigation and target recognition. Monopulse radar 3-D imaging techniques, interferometric inverse synthetic aperture radar 3-I) imaging technique, motion compensation of stepped-frequency signal in radar imaging, mosaic of range profiles produced by chirp-stepped-frequency signal and application of super-resolution in radar 3- D imaging have been developed in this thesis. Details are described as follows. In chapter 1, the background, significance, history and status in quo of 3-D imaging are introduced~ In Chapter 2, monopulse radar 3-I) imaging techniques are developed. The method combined TSAR with monopu]se angle measurement to make 3-D imaging is analyzed. For angle glint, the relationship between the multiplication of the imaginary part of regularized error signal by the radar-target distance and angle measurement error is analyzed. This relationship is used as the rule to judge whether angle glint occurs. For ship target, the effect of multi-dimensional rotation to Doppler frequency shift is analyzed and dechirp is proposed to separate scatterers. Imaging in two tracking systems is discussed. One is continuous tracking system. An angle sensor is proposed to record the angle tracking data, so random angle error in tracking can be obtained by curve fitness and amplitude random modulation in difference signal can be compensated. The other is stepped-tracking system where the antenna beam takes stillness in coherent processing intervals. Angle movement parameters are estimated by monopulse angle measurement based on range profile and amplitude modulation in difference signal is compensated. In chapter 3, interferometric inverse synthetic aperture radar 3-D imaging techniques are presented. 3-I) imaging in three cases is studied. In case 1, the antenna continuously tracks targets. The relationship between angle measurement error and angle tracking error is discussed and angle measurement algorithm based on range profile and TSAR image is presented. An angle sensor is proposed to record the angle tracking data, then random angle error in tracking is estimated by curve fitness and can be compensated before TSAR imaging. In case 2, the antenna tracks targets in step. It means the antenna beam holds stillness in coherent processing intervals, when an image is produced, the antenna turn an angle to track the target again. We show that Doppler frequency shift exists between antennas and alignment of ISAR images by correlation, frequency searching and angle parameters estimation is available. In case 3, the antenna holds stillness all the time. If the direction of the target can be estimated with other methods such as DOA method, the ambiguity of phases between antennas can be compensated. Chapter 4 is about motion compensation of TSAR imaging with stepped-frequency waveforms. To overcome the shortcoming of large amount of computation of method based on the rule of minimum image entropy and the multiple minimum points of method based on the rule of signal difference between clusters, a separated search of speed and acceleration method is proposed. Acceleration is estimated based on minimization of the cross-image entropy of echo signals, and speed is estimated based on maximization of the alignment of one- dimensional range profiks. The computational advantage of our methods over minimum image entropy methods is analyzed and the efficiency of our methods is shown with simulation result.