Method and apparatus to determine the direction to a transponder in a modulated backscatter communication system

• US 6,600,443 B2
• Filed: 10/18/2002
• Issued: 07/29/2003
• Est. Priority Date: 06/05/2000
• Status: Expired due to Term

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: TC License Limited
• Inventors: Landt, Jeremy A.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US10/273,159
• Publication Number:
  US 20030058155A1
• Time in Patent Office: 284 Days
• Field of Search: 342/42, 342/44, 342/46, 342/47, 342/51, 342/147, 342/149, 342/152, 342/156, 342/188, 340/825.36
• US Class Current: 342/42
• CPC Class Codes: G01S 3/043 Receivers
• CPC Class Codes: G01S 3/38 using adjustment of real or effective orientation of directivity characteristic of an antenna or an antenna system to give a desired condition of signal derived from that antenna or antenna system, e.g. to give a maximum or minimum signal G01S3/16, G01S3/28 take precedence
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

Methods and systems for determining the direction to a transponder are disclosed. The methods and systems include transmitting a first signal to an area where communications with a transponder is desired; producing a second signal desired from the first signal; receiving the second signal via a first and second antenna forming a difference signal from the second signal received via the first and second antennas; forming a third signal by adding the second signal received via the first antenna and the second signal received via the third antenna; delaying the difference signal; and comparing a fist polarity of the delayed difference signal with a second polarity of the third signal.

Claims

1. A method for determining the direction to an RF device comprising:

receiving a first signal from the RF device via first, second, and third antennas;

forming a difference signal from the first signal received via the first and second antennas;

delaying the difference signal; and

comparing a first polarity of the delayed difference signal with a second polarity of the first signal received via the third antenna.

2. The method of claim 1, further comprising:

determining that the RF device is to the left of the third antenna when the first and second polarities are the same.

3. The method of claim 1, further comprising:

determining that the RF device is to the right of the third antenna when the first and second polarities are opposite.

4. The method of claim 1, further comprising:

determining that the RF device is aligned with the third antenna when the difference signal is not detected by a receiver.

5. The method of claim 1, wherein delaying the difference signal comprises:

delaying the difference signal by 90 degrees.

6. The method of claim 1, further comprising:

positioning the third antenna in between the first and second antennas so that the distance in between the third and first antennas is the same as in between the third and second antennas.

7. The method of claim 1, further comprising:

connecting a first phase shifter to the output of the first antenna;

connecting a second phase shifter to the output of the second antenna;

setting a phase shift in the first and second phase shifters to have a same magnitude and an opposite polarity;

varying the magnitude of the phase shift in the first and second phase shifters; and

obtaining a value of the magnitude of the phase shift when the delayed difference signal is not detected by a receiver.

8. The method of claim 7, further comprising:

determining that an angle to the RF device is the obtained value of the magnitude of the phase shift.

9. A method for determining the direction to an RF device comprising:

receiving a first signal from the RF device via first and second antennas;

forming a difference signal from the first signal received via the first and second antennas;

forming a second signal by adding the first signal received via the first antenna and the first signal received via the second antenna;

delaying the difference signal; and

comparing a first polarity of the delayed difference signal with a second polarity of the second signal.

15. The method of claim 9, further comprising:

determining that the RF device is to the left of a third antenna located in between and aligned with the first and second antennas when the first and second polarities are the same.

16. The method of claim 9, further comprising:

determining that the RF device is to the right of a third antenna located in between and aligned with the first and second antennas when the first and second polarities are opposite.

17. The method of claim 9, further comprising:

determining that the transponder is aligned with a third antenna located in between and aligned with the fist and second antennas when the difference signal is not detected by a receiver.

10. A method for determining the direction to an RF device comprising:

receiving a first signal from the RF device via first and second antennas;

forming a difference signal from the first signal received via the first and second antennas;

connecting a first phase shifter to the output of the first antenna;

connecting a second phase shifter to the output of the second antenna;

setting a phase shift in the first and second phase shifters to have the same magnitude and opposite polarity;

varying the magnitude of the phase shift in the first and second phase shifters; and

obtaining a value of the magnitude of the phase shift when the difference signal is not detected by a receiver.

11. The method of claim 10, further comprising:

determining that an angle to the RF device is the obtained value of the magnitude of the phase shift.

12. A method for determining the direction to an RF device comprising:

receiving a first signal from the RF device via first and second antennas;

obtaining a difference of phases at the first and second antennas; and

determining an angle θ

to the RF device by using the equation

13. The method of claim 12, wherein the step of obtaining the difference in phases comprises:

performing a first quadrature detection of the first signal received via the first antenna;

performing a second quadrature detection of the first signal received via the second antenna;

linearly amplifying the first and second detected signals;

filtering the first and second amplified signals to isolate a modulation produced by the RF device;

digitizing the first and second filtered signals;

computing a first phase by calculating the arctangent of the ratio of a quadrature signal component of the first digitized signal to in-phase signal component of the first digitized signal;

computing a second phase by calculating the arctangent of the ratio of a quadrature signal component of the second digitized signal to the in-phase signal component of the second digitized signal; and

subtracting the second phase from the first phase.

14. The method of claim 12, wherein the step of obtaining the difference in phases comprises:

performing a first quadrature detection by mixing the first signal received via the first antenna with an LO reference signal;

performing a second quadrature detection by mixing the first signal received via the second antenna with the LO reference signal;

varying the LO reference signal over a phase range during a sweep time;

measuring a difference in timing between quadrature nulls corresponding to the first and second antennas;

forming a ratio of said difference in timing to said sweep time; and

multiplying said ratio by said phase range.