The Theory And Methods Of Moving Target Imaging For Stepped-frequency Radar

Being a wideband radar with high flexibility, high effectiveness and low cost, stepped-frequency radar (SFR) has been widely used in military and civil applications. However, due to its wide bandwidth and long coherent processing interval (CPI), stepped-frequency waveform (SFW) is very sensitive to Doppler effects. Therefore, non-cooperative moving target imaging is one of the bottlenecks of SFR signal processing. Based on this status in quo, this thesis is fully contained by the theory and methods of moving target imaging/profiling for SFR. The wideband acceleration echo model of SFR, the wideband acceleration ambiguity function (WAAF) of SFR, methods of high-range-resolution (HRR) profiling for moving targets, techniques of motion compensation for high-speed maneuvering targets, and key techniques for moving target imaging in clutter using high pulse repetition frequency (HPRF) SFR have therefore been deeply studied. The results of the researches mainly involve:1.According to the characteristics of wide bandwidth and long CPI of SFW, the wideband acceleration echo model of SFR has been analyzed. Thereafter, the WAAF of SFW has been defined and a fast computation method of SFW WAAF has been proposed. A series of characteristics of SFW WAAF have been revealed for the first time, including scaling factor of each dimension, and output characteristics considering either locally coupling mismatch or periodically ambiguous mismatch of parameters. Based on these characteristics, the real output behaviors of SFR correlation receiver have been generally disclosed, and the deficiencies of traditional narrowband ambiguity function and narrowband acceleration ambiguity function have been remedied.2.The principles and characteristics of two kinds of HRR profiling methods have been expatiated from new points of views. To solve the problem of range profiling non-cooperative moving targets, the adaptability to target motion of the HRR profile synthesis method and the frequency-domain bandwidth synthesis method has been compared for the first time, proving that the former method performs better. Therefore, focusing on the HRR profile synthesis method, signal invariant properties of scattering centers of moving targets have been proved. Thereupon, a new HRR profile synthesis method based on these invariant properties has been proposed, which sufficiently takes advantages of the information of multiple scattering centers and oversampling redundancies and has been verified by field measured data.3.The motion compensation principle for high-speed maneuvering targets in SFR has been analyzed. Based on linearly-stepped-frequency radar (LSFR) and high-speed uniform motion model, a fast motion parameter estimation method named two-dimensional time-domain cross-correlation has been proposed, which can also be generalized easily to the application of randomized-stepped-frequency radar (RSFR) and high-speed uniform-acceleration motion model. Based on LSFR and high-speed uniform-acceleration motion model, the velocity-acceleration coupling relationship in the time-domain correlation function has been analyzed and its difference to the velocity-acceleration coupling relationship in echo has been revealed. Thereupon, a new method for degrading two-dimensional velocity-acceleration parameter estimation to one dimensional parameter estimation as well as for decoupling the estimations of velocity and acceleration has been proposed.4. Several key techniques of moving target imaging using HPRF SFR have been studied. To solve the ambiguity of HRR profiles introduced by HPRF, the joint ESPRIT and spectrum matching score method has been proposed, which compensates the severe performance deterioration introduced by signal distortions due to narrowband filtering, and therefore simultaneously achieves HRR profile and unambiguous parameter estimation. To imaging moving target in heavy clutter, parameter restrictions for moving platforms have been analyzed. High resolution range-Doppler imaging method for SFR has been proposed, which can generate the range-Doppler image in a common sense but in SFR, and accomplish joint HRR and PD anti-clutter processing. Performance of parameter estimation based on range-Doppler image has been analyzed. The validity of the methods has been verified by field experiments.The research results of this thesis are meaningful for complementing radar signal ambiguity theory. Meanwhile, these results can satisfy non-cooperative target imaging and range profiling for various applications of SFR, such as defense penetration of ballistic missiles, interception of low-altitude high-speed targets, detection and interception of hedgehopping targets buried in clutter, battlefield surveillance, etc., and therefore have great values in military applications.