| Laser radar is one of the most effective technologies to process high precision information of 3D image. As an active depth information sensor, laser radar is combined by traditional radar and modern laser techniques. It has a series of special advantages, high angle resolution, high range resolution and high speed resolution, widely limits of speed measurement, muti-objective imaging, strong capability of anti-jamming, etc. In this paper the information of distance is obtained by LFM technology, at the same time the two-dimension plan information of the target is obtained by galvanometric scanner, then the three-dimension information is obtained by these two technologies. The technology of LFMCW has large product of timewidth and bandwidth, as a result high range resolution and high speed resolution in remote can be obtained. So the conflict between distance and range resolution in common radar is solved. In this paper the research is concentrated on speed and distance measurement heterodyning-FFT algorithm of LFM signal. And the feasibility is confirmed by simulation and experiment.Firstly, the structure of system of 1.55μm LFMCW laser radar is devised. At the same time, the properties of time domain and frequency domain of LFM signal is analyzed, then transmitting signal and target echo signal of LFM are simulated by soft-ware, and the relationship of timewidth, bandwidth of signal and the measured distance, range resolution and speed resolution are discussed.Secondly, the pulse compression principle of FLM signal is analyzed. And the processes of quadrature demodulation and matched filtering to the echo signal are simulated by MATLAB. The method of designing analog filter by MATLAB is introduced, and the effect by window technique to compressed pulse signal is analyzed. Take symmetrical triangular wave signal as a example, speed and distance measurement heterodyning-FFT algorithm of LFM signal is introduced, the heterodyning signal in time dominate is researched, then the experiment in different conditions which including different speed and different distance is done. At last the conclusion is got that symmetrical triangular wave can couple the speed and distance well.In the LFMCW distance measurement experiment, the relation of frequency of heterodyning signal between distance, bandwidth of modulating signal and modulation period is discussed. In condition of different bandwidths of modulating signal and different modulation period, we get four sets of data, and the heterodyning signal can be seen by oscillograph.The reasons of the deviation between theory and practical results are researched, the correctness of speed and distance measurement heterodyning-FFT algorithm of LFM signal is proved. |
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