Study On Digital Generation Methods For Ultra Wide-Band Radar Pulse-Compression Signals

Ultra wide-band (UWB) radar is a new kind of radar system which has been developed in recent years. It is a major evolution aspect of radar detecting techniques, and its researches and applications are one qualitative leap in the course of radar development. UWB radar, well known for its high range resolution, power penetration, low probability of intercept and robust jamming immunity, is paid more attention to and has a broad and important prospect in military and civilian applications and so forth. Among the researches on UWB radar techniques, the generation of UWB radar signals is a key and frontal subject. Taking example for linear frequency modulation (LFM) signals, this dissertation investigates the digital methods of generating UWB radar pulse-compression waveforms systematically and profoundly. The main content and creative work are summarized as follows:1. The three digital methods of generating LFM pulse-compression waveforms, including the single-bit generation method, the direct digital frequency synthesis (DDFS) method and the direct digital waveform synthesis (DDWS) method, and the analogue quadrature modulating technique and the solid-state frequency multiplication technique for widening frequency band, are studied in detail. The working principles, errors sources and performances of these methods are explored by systemic theoretical analyses and computer data simulations. These research conclusions indicate the emphases and directions in the work of designing and developing digital UWB-LFM radar pulse-compression signal generation systems, and they also lay a theoretical foundation for the implementations of UWB radar pulse-compression signal sources.2. The errors sources and their influences of digital UWB radar pulse-compression signal generation systems are investigated. First of all, the various errors sources of UWB waveform generation systems are generalized. Then, the corresponding mathematical models for the characteristics distortion of UWB waveform systems in the frequency domain, the deformation of LFM signals in the time domain, the phase errors in LFM waveform generators, the FM non-linearity of LFM signals, and the coherence of LFM signals are made respectively. Furthermore, the effects of these errors factors on the performance of produced signals are studied by theoretical analyses and computer emulations. These research achievements provide necessary theoretical bases and important experience references for the engineering designs, the performance analyses, the performance evaluations and the performance optimizations of UWB radar pulse-compression signal generation systems.3. Digital compensation methods and techniques for the distortions of UWB-LFM radar pulse-compression generation systems are researched systematically. In the first place, the all-around models for UWB waveform generation systems are made. Based on the linear system theory, and the flexibility and reliability of digital generation methods, the principle and the feasibility of digital compensation for waveform generation systems are analyzed. Afterwards, the digital correction methods for the distortion of digital baseband generation circuits, the non-idealization of quadrature modulators and the errors of frequency multipliers are orderly studied by theoretical deductions and computer simulation verifications. These digital correction methods presented above have an advantage of high accuracy of pre-distortion calibration. However, the transfer functions of each key part of UWB waveform generation systems must be precisely measured.4. A digital pre-distortion correction method according to the distortion degree of outputted signals in the time domain, which doesn't need to measure the transfer functions of UWB waveform generators, is put forward. And this digital correction method is investigated by theoretical derivations and computer simulation verifications. Although it adjusts the errors of generated signals approximately, it can significantly improve the quality and performance of outputted waveforms, and satisfy the requirements of radar systems. This method is simple and convenient, and can be easily popularized and applied in engineering practices.