Method and apparatus for improving the interrogation range of an RF-Tag

• US 6,590,498 B2
• Filed: 10/31/2001
• Issued: 07/08/2003
• Est. Priority Date: 10/19/1999
• Status: Expired due to Term

• Current Assignee: LGS Innovations LLC (CACI International Incorporated)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Helms, Howard David
• Primary Examiner(s): Lee, Benjamin C.
• Assistant Examiner(s): Nguyen, Tai T.
• Application Number:
  US09/999,390
• Publication Number:
  US 20020113709A1
• Time in Patent Office: 615 Days
• Field of Search: 340/572.7, 340/505, 340/573.1, 340/928, 340/825.45, 340/825.54, 343/720, 343/895, 343/866, 455/277.1, 455/41, 455/59, 455/62
• US Class Current: 340/572.7
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence

Abstract

A method for increasing the interrogation range of an RF Tag in a radio communication system using RF Tags with multiple reflecting antenna elements. The reflecting antenna elements are predeterminately positioned, and preferably aligned, with respect to each other in the direction of expected incident RF radiation. The reflecting antenna elements are sequentially pulsed on and off such that while the first reflecting antenna element is in a signal reflecting operating state, the remaining reflecting antenna elements are in a substantially non-reflecting state, and when the second reflecting element is in a reflecting operating state, the remaining reflecting elements are in a non-reflecting state, etc. The sequential pulsing and predetermined fixed spacing between the reflector elements generates constructive interference between the reflected signals of the reflecting antenna elements which increases the power of the resulting reflected signal.

Claims

1. A method of increasing an interrogation range in an RF-Tag monitoring system having an Interrogator and a plurality of reflecting antenna elements located on each of one or more tags for receiving RF signals of a wavelength (λ

) and a time period T from the Interrogator and reflecting back to the Interrogator modulated signals, wherein said plurality of reflecting antenna elements are spatially positioned along a path of activation, said method comprising the step of;

activating at least some of the reflecting antenna elements in said plurality along said path of activation for a duration of time so that a presently activated reflecting antenna element is positioned farther along the path of activation with respect to a previously activated reflecting antenna element.

2. The method set forth in claim 1, wherein said activating step comprises the step of sequentially activating at least some of the reflecting antenna elements in said plurality.

3. The method set forth in claim 1, wherein said activating step comprises activating at least some of the reflecting antenna elements for a duration of time so that an average activation time for each activated antenna element is T/N, where N is the number of activated antenna elements.

4. The method set forth in claim 1, wherein said plurality of reflecting antenna elements are located on one RF Tag.

5. The method set forth in claim 1, wherein said plurality of reflecting antenna elements are positioned about an axis at an average separation of λ

/2N, where N is the number of activated antenna elements.

6. The method set forth in claim 5, wherein said axis comprises a plurality of axes so that a group of reflecting antenna elements are positioned along each of said axes.

7. The method set forth in claim 6, further comprising the step of simultaneously activating the reflective antenna elements in each axially aligned group and measuring the strength of the reflected signal from said activated group to determine which axially aligned group provides a strong reflected signal.

8. The method set forth in claim 7, wherein each axially aligned group of reflective antenna elements has a length that is increased by adding additional reflective antenna elements.

9. The method set forth in claim 1, wherein said reflecting antenna elements are positioned in a staggered arrangement about an axis at an average separation of λ

/2N, where N is the number of activated antenna elements.

10. The method set forth in claim 1, wherein said activating step further comprises activating said at least some of the reflecting antenna elements so that only one reflecting antenna element is activated at any given time.

11. A method for increasing an interrogation range in an RF Tag monitoring system utilizing a Luneberg lens reflector as an RF Tag for receiving and reflecting RF signals, the Luneberg lens having a plurality of reflecting elements for receiving RF signals of a wavelength (λ

) and a time period T and for reflecting modulated signals derived from the received RF signals, wherein said plurality of reflecting elements are positioned along a path of activation, said method comprising the step of;

activating at least some of the reflecting elements in the plurality along said path of activation for a duration of time so that a presently activated antenna element is positioned farther along the path of activation with respect to a previously activated reflecting antenna element.

12. The method set forth in claim 11, wherein said step of activating generates a phase difference between the signals reflected from the plurality of reflecting elements.

13. An RF Tag communication system, comprising:

an Interrogator for transmitting RF signals having a carrier wavelength (λ

) and a period (T);

a plurality of reflecting antenna elements located on each of one or more tags for receiving RF signals of the wavelength (λ

) and the time period T from the Interrogator and reflecting back to the Interrogator modulated signals, said plurality of reflecting antenna elements being spatially positioned along a path of activation; and

means for activating at least some of the reflecting antenna elements in said plurality along said path of activation for a duration of time so that a presently activated reflecting antenna element is positioned farther along the path of activation with respect to a previously activated reflecting antenna element.

14. The system of claim 13, wherein said activating means comprises means for sequentially activating at least some of the reflecting antenna elements in said plurality.

15. The system of claim 13, wherein said activating means comprises activating at least some of the reflecting antenna elements for a duration of time so that an average activation time for each activated antenna element is T/N, where N is the number of activated antenna elements.

16. The RF Tag communication system in accordance with claim 13, wherein the plurality of reflecting antenna elements are disposed on a single RF Tag.

17. The RF Tag communication system in accordance with claim 13, wherein said activating means comprises a processor.

18. The RF Tag communication system in accordance with claim 13, wherein said plurality of reflecting antenna elements is positioned so that the antenna elements are axially aligned with each other in a direction of expected incident receipt of the RF interrogating signals.

19. The RF Tag communication system in accordance with claim 13, wherein said reflecting antenna elements are positioned about an axis at an average separation of λ

/2N, where N is the number of activated antenna elements.

20. The RF Tag communication system in accordance with claim 19, wherein said axis comprises a plurality of axes so that a group of reflecting antenna elements are positioned along each of said axes.

21. The RF Tag communication system in accordance with claim 20, wherein said activating means is operable to simultaneously activate the reflective antenna elements in each axially aligned group so that the strength of the reflected signal from each said activated group can be evaluated to determine which axially aligned group provides a strong reflected signal.

22. The RF Tag communication system in accordance with claim 13, wherein said reflecting antenna elements are positioned in a staggered arrangement about an axis at an average separation of λ

/2N, where N is the number of activated antenna elements.

23. A reflective communicator for receiving a signal from an Interrogator and reflecting the received signal back to the Interrogator, said reflective communicator comprising:

a plurality of reflective antenna elements disposed along a direction of activation; and

means for activating at least some of the reflective antenna elements in said plurality along said path of activation so that a presently activated reflecting antenna element is positioned farther along the path of activation with respect to a previously activated reflecting antenna element.

24. The communicator of claim 23, wherein said activating means comprises means for sequentially activating at least some of the reflecting antenna elements in said plurality.

25. The communicator is accordance with claim 23, wherein the signal from the Interrogator has a wavelength and a period T and wherein said activating means comprises activating at least some of the reflecting antenna elements for a duration of time so that an average activation time for each activated antenna element is T/N, where N is the number of activated antenna elements.

26. The communicator in accordance with claim 23, wherein the plurality of reflecting antenna elements are disposed on a single RF Tag.

27. A method of compensating for misalignment between an interrogation signal produced by an interrogator and a reflecting element array comprising a plurality of reflecting antenna elements by activating selected numbers of the plural reflecting antenna elements during a series of predetermined activation time periods T, comprising the steps of:

(a) activating a selected number of the plural reflecting antenna elements during an activation time period T to receive and reflect the interrogation signal back to the interrogator;

(b) measuring the strength of the reflected interrogation signal from step (a);

(c) repeating each of steps (a) and (b) for subsequent activation time periods T using different selected numbers of the plural antenna elements; and

(d) using the measured strengths of the reflected interrogation signals from said repeated steps (b) to determined a desired number of the plural antenna elements to be activated to produce a desired strength reflected signal.