Patent ID: 7049965

Claim:
A surveillance system comprising: a first loop antenna; a second loop antenna substantially orthogonal to said first loop antenna, said first and second loop antennas being inductively couplable with a tag through magnetic fields; a first attenuator driving said first loop antenna; a second attenuator driving said second loop antenna; a z ramp generator to provide a z control signal to said first attenuator; a y ramp generator to provide a y control signal to said second attenuator; a signal processing component for estimating an orientation of said tag based on a magnitude of an inductively coupled modulated signal from said tag as an orientation of a coupling field generated from said first and second loop antennas is scanned through a range of angles; a splitter coupled to said signal processing component, wherein said signal processing component comprises: a bandpass filter coupled to said splitter; an envelope detector coupled to said bandpass filter; a modulation minimum detector coupled to said envelope detector; and an angle calculator coupled to said modulation minimum detector, said angle calculator configured to estimate said orientation.