| Inverse synthetic aperture radar (ISAR) is a useful all-weather high-resolution radar system for moving target imaging and target recognition in a long-distance all-weather conditions. It is with great military and civil values. To meet the rising demand, the researches about ISAR technologies are rapidly developing. The main research in this dissertation is the new technologies of the ISAR imaging, which including the new waveforms, imaging algorithm, imaging system and the scatterering center extraction. The summary of this dissertation is as follows:Chapter 1 is the introduction. It reviews the history of ISAR development and introduces the dissertation's research background and main work.Chapter 2 introduces the principles of high range and cross-range resolution in ISAR imaging. It overviews the research achievements about ISAR imaging algorithm both at home and abroad.Chapter 3 studies the processing of SFW (stepped frequency waveform). Based on the discussion of SRP (synthetic range profile) method, two target extraction algorithm base on CLEAN technique are proposed. The two-dimensional reference function is constructed with the emitted signal. The parameters (i.e., position, amplitude and velocity) of a point scatterer can be found by global searching with genetic algorithm. And an iterative CLEAN processing is used to eliminate the extracted point from the received data of one SFW burst. Then the high range resolution profile (HRRP) of the target can be reconstructed with the estimated parameters. Finally the effectiveness of the algorithm is verified by the simulation results.Chapter 4 introduces the bandwidth synthetic method (time domain and frequency domain bandwidth synthetic) of SFW and two applications, the ISAR imaging of high speed moving targets and ship targets based on SFW. First of all, the time domain and frequency domain bandwidth synthetic methods are introduced. Then using the frequency domain bandwidth synthetic method, the ISAR imaging procedure of high speed moving target based on SFW are given out. The simulation results fully demonstrate the effectiveness of the proposed methods. Finally, a simple and successful bandwidth synthetic processing of SFW for ISAR imaging of ship targets is presented. The high range resolution is obtained by combining the sub-pulses of SFW in the frequency domain. The overlapping bandwidth of the two adjacent sub-pulses is used to estimate phase errors. And the usual motion compensation approach is avoided if the band coherent processing is used. Furthermore, the experimental results of the ship target are shown.Chapter 5 presents a novel ISAR imaging algorithm for ship target. The conventional ISAR imaging method is based on the instantaneous Doppler of scatterers. For a high maneuvering target, such as ship with yaw, pitch and roll motions, the instantaneous Doppler of scatterers may be small and the satisfactory may be unobtainable at some time instants. Meanwhile, a large instantaneous chirp rate is often present for the same scatterer at the same instant. In order to get some additional information of target, a novel ISAR imaging approach, referred to as range instantaneous chirp (RIC), is proposed based on instantaneous chirp rate of scatterer to provide cross range resolution. Therefore, RIC image is generated with a different 'view'. It may provide some additional information and a better target recognition and identification can be achieved for high maneuvering targets. The proposed RIC algorithm is verified by results of simulation and raw radar data.Chapter 6 studies the bistatic radar system for ISAR imaging. The model of bistatic ISAR is analyzed in wave-number domain. Comparing with the monostatic radar, the bistatic angle and azimuth angle of equivalent LOS (line of sight), these two angles demonstrate the characteristic of bistatic radar. Because the variation of the two angles is changed with the target's location, the observation region is partitioned into four parts using the bistatic angle isoline. The proper bistatic ISAR imagery algorithm in a specific region can be determined through the discussion of these two angles in this region.The range migration problem may occurred due to the bistatic angle change when the high resolution bistatic ISAR image need to be obtained. The critical condition that the variation of bistatic angle can be ignored is given out, and the range migration correction method is presented. The correctness of the analysis in this Chapter are proved by simulation results.Chapter 7 introduces the 3D scatterering center extraction and image reconstruction of target. The model of interferometric inverse synthetic aperture radar (InISAR) three-dimensional imaging is proposed when the angle between the target and the antenna axis is considerable. And the motion compensation scheme is discussed in detail. To deal with the measurement error induced by the motion compensation error, the phase of the target's barycentre is estimated to compensate the phase differences. The measured scatterers' height and width are wrong because they are not obtained in rectangular coordinates. The formula to transform the measured coordinates into rectangular coordinates and generate a correct 3D image is given in this chapter. Finally, the simulation results are given.Chapter 8 is the summary of the dissertation. It also discusses future research areas to be further studied.
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