Multiple frequency through-the-wall motion detection and ranging using a difference-based estimation technique

Apparatus for the estimation of the range to a moving object, comprising:

• a two-tone radar for generating continuous wave energy simultaneously at two different frequencies;
• a single antenna coupled to said radar for simultaneously projecting continuous wave energy therefrom;
• a pair of mixers coupled to said antenna and said radar for generating waveforms corresponding respectively to the phase difference between outgoing and reflected energy at said antenna for each of said two different frequencies;
• and,
• a range estimation unit coupled to said pair of mixers for estimating range to said moving object, said range estimation unit including a predictor for generating from a temporal waveform corresponding to the phase difference between outgoing and reflected energy at the second of said frequencies a series of range dependent waveforms corresponding to an expected temporal phase difference of returned continuous wave energy at a first one of said frequencies, and a waveform matching unit for establishing a match between one of said range-dependent waveforms and the output of the mixer associated with said first one of said frequencies.