Frequency shift keying radar with ambiguity detection

A method of removal of ambiguity in distance of a radar apparatus of the kind in which a carrier frequency is transmitted, the method comprising the steps of:

• a) modulating the carrier frequency such that a sequence of first and second frames are transmitted with an initial transmittal of
• a first frame comprising a sequence of at least two different frequencies and a subsequent transmittal of
• a second frame comprising at least two different frequencies, the second signal differing from the first signal, the first and second frames being transmitted continuously and alternately;
• c) receiving an echo signal corresponding to the transmitted signal which has been reflected from a target;
• and
• d) processing the echo signal together with the transmitted signal to determine the distance to the target.

A range detection apparatus comprising:

• a transmitter adapted to transmit a microwave signal;
• a receiver adapted to receive an echo signal reflected from a target which corresponds to a portion of said transmitted signal;
• a signal generator adapted to generate a drive signal to be applied to said transmitter to produce said transmitted signal, said signal generator producing a drive signal which includes a first signal frame comprising at least two frequencies and a second signal frame also comprising at least two frequencies, said second signal frame differing from said first signal frame, and
• a processor adapted to process said echo signal together with said transmitted signal so as to determine distance to said target that produced said echo signal, said processor also adapted to compare an average frequency of a transmitted frame with an average frequency of a frame of said echo signal to produce a Doppler signal over time which indicates the relative velocity of the apparatus and said target that produces said echo signal, said processor further adapted to detect the presence of more than one peak in said Doppler signal and, in the event that a second peak is detected, to provide an indication that a target that produced the echo signal is a distant target or at a close range.