Method and apparatus for object tracking, on the basis of the doppler shift

摘要

Detection of moving targets by detection of the doppler shift of radiation scattered or reflected by the target when illuminated by such radiation, is liable to give a false target indication if an interfering signal is received which has a frequency difference from the transmitted radiation lying in the range of the expected doppler shift. The problem is found in intruder alarm systems which use doppler shift detection. To mitigate the problem, the transmitted radiation is frequency modulated, by noise or by an audio tone, so that the scattered or reflected radiation has a coherence with the transmitted radiation but the interfering signal does not. The principle is applicable to both electromagnetic and pressure-wave radiation. In one intruder alarm system two separately operating, doppler shift detector units are coupled together to give a warning signal only when both indicate an intruder. Application of the above principle to one or both units prevents them giving false alarms due to mutual interference.