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System and method for estimating range to an RFID tag

  • US 9,841,500 B2
  • Filed: 03/07/2016
  • Issued: 12/12/2017
  • Est. Priority Date: 02/03/2012
  • Status: Active Grant
First Claim
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1. A system for determining distance from a plurality of antennas to a backscatter RFID tag comprising:

  • a transmitter for transmitting a transmitted modulated signal to the tag via first and second antennas,a first receiver for receiving a first modulated backscattered signal having a first delay from the tag via said first antenna;

    a second receiver for receiving a second modulated backscattered signal having a second delay from the tag via said second antenna;

    a first linear adaptive combiner which is a delay line having first delay line taps with first controllable weights on each first delay line tap, and outputs that are summed and subtracted from a reference to produce a first error signal; and

    a second linear adaptive combiner which is a delay line having second delay line taps with second controllable weights on each second delay line tap, and outputs that are summed and subtracted from said reference to produce a second error signal;

    wherein modulation in the backscattered signal received by said first antenna is input to said first adaptive linear combiner, and said transmitted modulated signal is said reference to said first adaptive linear combiner;

    wherein modulation in the backscattered signal received by said second antenna is input to said second adaptive linear combiner, and said transmitted modulated signal is said reference to said second adaptive linear combiner;

    wherein the first and second controllable weights for said taps of said first and second linear adaptive combiners are approximately zero for all of said taps except for respective first and second combiner taps corresponding to the first and second delays of the backscattered signal; and

    wherein the distance from the RFID tag to each of said antennas is determined from said first and second delays.

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