Distributed RFID antenna array utilizing circular polarized helical antennas

• US 7,614,556 B2
• Filed: 05/04/2006
• Issued: 11/10/2009
• Est. Priority Date: 11/05/2004
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: GOLIATH Solutions LLC (Osa Acquisition, LLC)
• Inventors: Overhultz, Gary L., Hardman, Gordon E., Pyne, John W., Strazdes, Edward J.
• Primary Examiner(s): WALSH, DANIEL I
• Application Number:
  US11/417,768
• Publication Number:
  US 20060208080A1
• Time in Patent Office: 1,286 Days
• Field of Search: 235378-380, 235/385, 235/451, 235/487, 235/492, 235/493, 340/572.1, 340/572.3, 340/572.7, 705/22, 705/20, 705/25, 705/64, 705/451, 705/487, 705/492, 705/493, 343/895, 343/572.1, 343/572.7
• US Class Current: 235/451
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil

Abstract

In accordance with the teachings described herein, RFID systems are provided that include a distributed RFID antenna array utilizing one or more circular polarized helical antennas. A plurality of RFID tags may be used, with each RFID tag including a linear polarized antenna for communicating RFID tag signals. One or more receiver antennas may be used for receiving the RFID tag signals from the RFID tags. An RFID tag signal reader may be used to process RFID tag signals received by the receiver antennas. In one example, the receiver antennas may include a circular polarized helical antenna element. One or more transmitter antennas may be used for transmitting an RF signal to the plurality of RFID tags, the transmitter antennas including a circular polarized helical antenna element. A transmitter may be used to generate the RF signal for transmission by the transmitter antennas. In one example, the RFID tag signal reader and the transmitter may be included in a single reader/transmitter unit.

Claims

1. A radio frequency identification (RFID) system, comprising:

a plurality of RFID tags, each of the plurality of RFID tags including a linear polarized antenna for communicating an RFID tag signal;

at least one receiver antenna for receiving the RFID tag signals, the receiver antenna including a circular polarized helical antenna element;

an RFID tag signal reader coupled to the at least one receiver antenna that processes the RFID tag signals;

a transmitter antenna for transmitting an RF signal to the RFID tag, the transmitter antenna including a circular polarized quadrifiler helical antenna element; and

a transmitter coupled to the at least one transmitter antenna that generates the RF signal;

wherein the RFID tag communicates the RFID tag signal in response to receiving the RF signal from the transmitter antenna;

wherein the plurality of RFID tags include a first tag and a second tag, the transmitter antenna being configured to apply a first gain on axis to the first tag and a second gain to the side of axis to the second tag, where the second gain is greater than the first gain.

2. The system of claim 1, wherein the receiver antenna is a single turn helix antenna.

3. The system of claim 1, wherein the transmitter antenna is a single turn quadrafilar helix antenna.

4. The system of claim 1, wherein the RF signal transmitted by the transmitter antenna includes a carrier wave that is modulated by the RFID tag to generate the RFID tag signal.

5. The system of claim 2, wherein the receiver antenna includes:

a dielectric core; and

an antenna element having a single radiating arm that extends in a spiral pattern around the dielectric core.

6. The system of claim 5, wherein the receiver antenna further includes an antenna backplane that adds directivity to a circular polarized radiation pattern of the antenna element.

7. The system of claim 5, wherein the receiver antenna further includes an amplifier circuit coupled to the antenna element.

8. The system of claim 2, wherein the receiver antenna includes:

a dielectric structure; and

an antenna element having a single radiating arm that is attached to the dielectric structure using one or more support structures.

9. The system of claim 8, wherein the receiver antenna further includes an antenna backplane that adds directivity to a circular polarized radiation pattern of the antenna element.

10. The system of claim 8, wherein the receiver antenna further includes an amplifier circuit coupled to the antenna element.

11. The system of claim 3, wherein the transmitter antenna includes:

a dielectric core; and

an antenna element attached to the dielectric core, the antenna element including four radiating arms that extend in a helical pattern from a common junction.

12. The system of claim 11, wherein the four radiating arms are formed from two antenna wires that are bonded at the common junction.

13. The system of claim 11, wherein the transmitter antenna further includes an antenna backplane that adds directivity to a circular polarized radiation pattern of the antenna element.

14. The system of claim 11, wherein the transmitter antenna further includes an amplifier circuit coupled to the antenna element.

15. The system of claim 1, wherein the transmitter and the RFID tag signal reader are included in a single reader/transmitter unit.

16. The system of claim 4, wherein the linear polarized antenna includes:

a first antenna element;

a second antenna element; and

a switching circuit for selectively coupling the first antenna element with the second antenna element;

when coupled together by the switching circuit, the first and second antenna elements forming a single antenna element that reflects the RF signal transmitted by the transmitter antenna; and

when not coupled together by the switching circuit, the first and second antenna elements absorbing at least a portion of the RF signal transmitted by the transmitter antenna.

17. The system of claim 1, wherein the RFID tag signal reader processes the RFID tag signals to determine an identification associated with the RFID tag and encoded in the RFID tag signal.

18. The system of claim 1, wherein the RFID tag signal reader processes the RFID tag signals to determine a location of the RFID tags.

19. The system of claim 1, wherein the RFID tag signal reader processes the RFID tag signals to determine an amount of time that the RFID tags are present within a facility.

20. A distributed radio frequency identification (RFID) antenna array system, comprising:

at least one transmitter antenna for transmitting RF signals, the transmitter antenna including a circular polarized quadrifiler helical antenna element;

a plurality of RFID tags, each of the plurality of RFID tags including a linear polarized antenna for receiving the RF signals and for transmitting RFID tag signals, the RFID tag signals being transmitted by the at least one of said plurality of RFID tags in response to receiving the RF signals;

a plurality of receiver antennas for receiving the RFID tag signals from the at least one RFID tag; and

a single reader/transmitter unit coupled to the at least one transmitter antenna and the plurality of receiver antennas, the reader/transmitter unit generating the RF signals for transmission by the at least one transmitter antenna and processing the RFID tag signals received by the plurality of receiver antennas;

wherein the distributed RFID antenna array system is included within a designated area of a retail facility, the designated area including a plurality of sub-areas;

wherein the plurality of RFID tags are located in the designated area with multiple RFID tags being located in each of the plurality sub-areas;

wherein one of the plurality of receiver antennas is located in each of the plurality of sub-areas;

wherein the at least one transmitter antenna is positioned to illuminate a plurality of RFID tags in each of the plurality of sub-areas with RF signals causing the one receiver antenna in each of the plurality of sub-areas to receive RFID tag signals from illuminated RFID tags; and

wherein the at least one transmitter antenna is configured to apply a first gain on axis of the circular polarized quadrifiler helical antenna element and to apply a second gain off axis of the circular polarized quadrifiler helical antenna element, where the first gain is less than the second gain.

21. The system of claim 20, wherein the RF signals transmitted by the transmitter antenna include carrier waves that are modulated by the plurality of RFID tags to generate the RFID tag signals.

22. The system of claim 20, wherein the transmitter antenna includes a single turn quadrifiler helix antenna.

23. The system of claim 21, wherein the linear polarized antenna in the plurality of RFID tags includes:

a first antenna element;

a second antenna element; and

a switching circuit for selectively coupling the first antenna element with the second antenna element;

when couple together by the switching circuit, the first and second antenna elements forming a single antenna element that reflects the RF signals transmitted by the transmitter antenna;

when not coupled together by the switching circuit, the first and second antenna elements absorbing at least a portion of the RF signals transmitted by the transmitter antenna.

24. A distributed radio frequency identification (RFID) antenna array system, comprising:

at least one transmitter antenna for transmitting RF signals, the transmitter antenna including a circular polarized helical antenna element;

a plurality of RFID tags, each RFID tag including a linear polarized antenna for receiving the RF signals and for transmitting RFID tag signals, the RFID tag signals being transmitted by the RFID tags in response to receiving the RF signals;

a plurality of receiver antennas for receiving the RFID tag signals from the RFID tags; and

means for generating the RF signals for transmission by the at least one transmitter antenna; and

means for processing the RFID tag signals received by the plurality of receiver antennas;

wherein the distributed RFID antenna array system is included within a designated area of a retail facility, the designated area including a plurality of sub-areas;

wherein the plurality of RFID tags are located in the designated area with multiple RFID tags being located in each of the plurality of sub-areas;

wherein one of the plurality of receiver antennas is located in each of the plurality of sub-areas;

wherein the at least one transmitter antenna is positioned to illuminate RFID tags in each of the plurality of sub-areas with RF signals causing the one receiver antenna in each of the plurality of sub-areas to receive RFID tag signals from illuminated tags; and

wherein the at least one transmitter antenna is configured to apply a first gain on axis of the circular polarized quadrifiler helical antenna element and to apply a second gain off axis of the circular polarized quadrifiler helical antenna element, where the first gain is less than the second gain.

25. The system of claim 24, wherein at least one of the plurality of RFID tags is a switched backscatter RFID tag.

26. The system of claim 25, wherein the switched backscatter RFID tag comprises:

a first antenna segment;

a second antenna segment;

means for coupling the first antenna segment to the second antenna segment to reflect the RF signals; and

means for decoupling the first antenna segment from the second antenna segment to absorb the RF signals.