Ultra-wideband Signal Waveform And Its Synthetic Aperture Radar Imaging Study

Ultra-Wide Band (UWB) radar is paid more attention to due to its great capabilities in high range resolution, robust anti-jamming and low probability of interception. In these years, Department of Defense of United States is always treating it as the key technique. With the development of modern weapon and the progress of microwave remote sensing technique, Ultra-Wide Band Synthetic Aperture Radar (UWB SAR) has become the hot field in the radar world.For radar is a complicated electronic system, the implementation of UWB will be subject to the level of electronic hardware. The large instantaneous bandwidth of UWB return causes great trouble to receiver. The dissertation is focused on UWB waveforms, which achieve UWB return without increasing the instantaneous bandwidth, and signal processing to generating SAR images with the desired waveform.Based on radar resolution principles, the factors working on SAR resolution are discussed. The waveforms are classified by ambiguity function, and the principle of waveform design is introduced.The stepped-frequency waveform design and stepped-frequency SAR imaging are discussed detailedly. The main work is given as follows: the stepped-frequency waveform synthesizing the wideband signal, the synthetic range profile (SRP) by IFFT, the range resolution of stepped-frequency waveform, the effect of the radial velocity on the SRP, the radial velocity compensation, ambiguity function, waveform design and stepped frequency SAR imaging and so on. The revised range spread function is validated by simulation. The method to design waveform and SAR system is described, and the steps of SAR imaging are presented.The stepped-chirp waveform and stepped-chirp SAR imaging are presented in detail. The UWB return is synthesized by a burst of narrow bandwidth chirp pulses whose carrier frequencies sequentially change. The effect of the radial velocity on synthetic spectrum and synthetic range profile is discussed, and the velocity compensation method is described. The ambiguity of stepped-chirp is presented and used to design the waveform. Furthermore, the stepped-chirp SAR system design and SAR imaging are discussed. Compared with chirp and stepped-frequency waveform, the advantages of stepped-chirp waveform are presented.The above waveforms discussed are to synthesize the WB or UWB with narrow band pulses. Assuming the transmitting UWB linear frequency modulation (Chirp), dechirp processing is introduced, and the method involved to obtain high resolution by reducing the IF bandwidth is presented. Furthermore, dechirp processing used to SAR imaging is discussed, and the processing steps are described.