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

• US 6,476,756 B2
• Filed: 06/04/2001
• Issued: 11/05/2002
• 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:
  US09/872,003
• Publication Number:
  US 20020008656A1
• Time in Patent Office: 519 Days
• Field of Search: 342/42, 342/44, 342/46, 342/47, 342/51, 342/147, 342/149, 342/152, 342/165, 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 a transponder comprising:

transmitting a first signal to an area where communications with a transponder is desired;

producing a second signal derived from the first signal;

receiving the second signal via first, second, and third antennas;

forming a difference signal from the second 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 second signal received via the third antenna.

2. The method of claim 1, further comprising:

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

5. The method of claim 1, further comprising:

receiving the second signal via fourth and fifth antennas;

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

delaying the second difference signal; and

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

6. The method of claim 1, whereby delaying the difference signals comprises

delaying the difference signal by 90 degrees.

7. A method for determining the direction to a transponder comprising:

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 receive 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.

8. The method of claim 7, further comprising:

determining that the transponder 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.

9. The method of claim 7, further comprising:

determining that the transponder 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.

10. The method of claim 7, further comprising:

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

11. A system for determining the direction to a transponder comprising:

a first antenna for transmitting a first signal to the transponder;

second and third antennas for receiving a second signal from the transponder;

means for adding the second signal received by the second antenna with the second signal received by the third antenna to produce a sum signal;

means for subtracting the second signal received by the second antenna from the second signal received by the third antenna to produce a difference signal;

means for delaying the difference signal; and

a comparator for comparing a first polarity of the difference signal with a second polarity of the sum signal.

12. The system of claim 11, further comprising:

a detector for detecting the delayed difference signal.

13. A system for determining the direction to a transponder comprising:

a first and a second antenna for receiving a signal from the transponder;

means for adding the signal received by the first antenna with the signal received by the second antenna to produce a sum signal;

means for subtracting the signal received by the first antenna from the signal received by the second antenna to produce a difference signal; and

a processor for comparing the difference signal with the sum signal to determine the direction to the transponder.