Transponder system and method

Abstract

A system and method for determining the range between a receiver of a radio frequency signal and a transmitter of the signal includes transmission of a ranging signal having a grossly timed trigger followed by a chirp waveform. In response to receipt of the leading edge of the grossly timed trigger, the receiver of the ranging signal generates a first reference chirp at about the same time as the expected time of receipt of the chirp waveform, and thereafter compares the two chirps to provide a time correction signal (it being known that when two identical chirp signals, one time delayed from the other, are mixed, the resulting signal will have a frequency proportional to the amount of delay between the two chirp signals.) The time correction signal is used to correct the timing of an outgoing corrected chirp that is to be used to determine range between the transmitter and receiver based on a time of arrival. The corrected signal is received at the transmitter and compared to a further reference chirp that is generated at a known time. The comparison of the received signal to the reference provides a signal related to a time difference between receipt of the corrected signal and the further reference chirp in order to determine a range between the transmitter and the receiver.