Patent ID: 6824480
Filing Date: 2004-11-30
Classification: A63B

Abstract:
A system for determining coarse and fine locations of an object, consisting of the following elements:(a) Four or more antennas, arranged in two or more closely spaced pairs dispersed in or around an area to be covered; (b) Downconvertors or receivers attached to each of the antennas, with local oscillators of the downconvertors in all the receivers derived from a single reference; (c) Phase locked loops to stabilize and reject noise in the downconverted signals; (d) Phase detectors to determine phase difference between a received signal in each pair of antennas, providing coarse location through intersection of directions of arrival; (e) Phase detectors to determine phase difference between a received signal in antennas not in the same pair, providing a set of intersections of loci of constant phase difference; (f) Resolution of the fine location through selection among the intersections of loci of constant phase difference, based on the coarse location obtained in (d); (g) A transmitter in the object to be tracked.