| Ultra-wideband(UWB) radar is characterized with high range resolution, good penetrating ability and strong anti-interference ability, which has been widely applied in many fields such as the accurate positioning, target tracking, imaging, detection and so on. Traditional UWB radar transmits signal by radio or cable, which is higher in energy loss. And the transmission distance is limited in a few or dozens of meters, which severely limits the range of radar. To enlarge the range of radar signal, this paper proposes the method of microwave photonic technology combined with ultra-wideband radar to realize the objective of signal remote transmission and precise detection by using the optical fiber with low loss and high bandwidth as the transmission medium. It provides a new technical method to detect target in hostile environment such as snow-capped mountain, isolated island, fuel storage warehouse and so on.This paper studies remote imaging radar system based on ultra-wideband chaotic signal generation and radio over fiber. The main research includes:1. By comparing the generation ways of ultra-wideband chaotic signal, we select Colpitts oscillator circuit, which has broad prospects, as the ultra-wideband chaotic signal source. And by conducting numerical simulation and experimental research, we analyze the correlation properties and ambiguity function of ultra-wideband chaotic signal.2. We put forward the remote imaging radar system based on ultra-wideband chaotic signal generation and radio over fiber. The system includes the central station, optical fiber links and the base station. In central station, UWB chaotic signal is generated and processed. Then the signal is transmitted by optical fiber links which connect the central station and the base station. In the base station, the target is detected. Photoelectric conversion is needed between the links of the central and base station.3. The remote imaging radar system based on ultra-wideband chaotic signal generation and radio over fiber is simulated and proved to be feasible. Through studying the effect of chaotic signal in optical fiber transmission, we build the theoretical model of optical fiber transmission and analyze the time series and spectrum characteristics of the chaotic signal before and after transmission. Then we build the simulation model of target imaging in free space and compare the imaging results of the chaotic signal before and after transmission. Finally the experiment proves that the optical fiber transmission has little influence on the performance of radar imaging.4. By setting up remote imaging radar system based on ultra-wideband chaotic signal, the experiment implements ranging, imaging of the static single and binocular targets as well as the tracking of moving target. The range and azimuth resolution of the system are 6 cm and 8 cm respectively. They are discussed that the transmission characteristics of chaotic signal in radar system and space, the relationship between optical fiber transmission distance and the correlation properties, the peak side-lobe level of chaotic signal, the relationship between acquisition bandwidth and range resolution. |
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