PLANAR DISTRIBUTED RADIO-FREQUENCY IDENTIFICATION (RFID) ANTENNA ASSEMBLIES

• US 20090184827A1
• Filed: 01/18/2008
• Published: 07/23/2009
• Est. Priority Date: 01/18/2008
• Status: Active Grant

• Current Assignee: TE Connectivity Solutions GmbH (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Laird Technologies Incorporated (DuPont de Nemours, Inc.)
• Inventors: Petropoulos, Athanasios
• Granted Patent: US 7,796,041 B2
• Time in Patent Office: Days
• US Class Current: 340/572.700
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40

Abstract

Disclosed are exemplary embodiments of passive radio-frequency identification (RFID) readers operable for creating a relatively uniform near field adjacent a planar surface for reading RFID tags generally above the planar surface. The RFID reader may include a plurality of antenna elements distributed in an array underneath the planar surface. A central antenna element may be located within the array generally between two or more perimetric antenna elements. A network may distribute electromagnetic energy to the antenna elements such that a current phase of at least one perimetric antenna element is out of phase with and lagging a current phase of the central antenna element. Alternatively, the perimetric antenna elements may be parasitically coupled to the central antenna element, such that a current phase of at least one perimetric antenna element is out of phase with and lagging a current phase of the central antenna element.

Claims

1. A passive radio-frequency identification (RFID) reader operable for creating a relatively uniform near field adjacent a planar surface for reading RFID tags generally above the planar surface, the RFID reader comprising:

a plurality of antenna elements distributed in an array underneath the planar surface, and including;

two or more perimetric antenna elements;

a central antenna element located within the array generally between the perimetric antenna elements;

a network for distributing electromagnetic energy to the antenna elements such that a current phase of at least one of the perimetric antenna elements is out of phase with and lagging a current phase of the central antenna element;

whereby the antenna elements are capable of being turned on at different times for avoiding high far field gain, such that an RFID tag is activated from a corresponding one of the antenna elements that is substantially directly underneath the RFID tag at the time the corresponding antenna element is turned on.

2. The RFID reader of claim 1, wherein at least one of the antenna elements is configured with a dual linear polarization, linear polarization, or circular polarization.

3. The RFID reader of claim 1, wherein the plurality of antenna elements comprises a 3×

3 array of nine patch-antennas such that there are eight perimetric patch-antennas generally about one central patch-antenna that is generally centrally located within the array relative to the eight perimetric antenna elements.

4. The RFID reader of claim 1, wherein the plurality of antenna elements comprises a 1×

3 array of three patch-antennas such that there is one central patch-antenna generally centrally located between two perimetric patch-antennas.

5. The RFID reader of claim 4, wherein the central patch-antenna is fed with a voltage of one volt with zero degree delay, and wherein each perimetric patch-antenna is fed with a voltage of 0.25 volts with 100 degrees phase delay.

6. The RFID reader of claim 1, wherein each antenna element is fed by a port.

7. The RFID reader of claim 1, wherein the RFID reader is operable for creating a substantially uniform near field adjacent a planar surface having a length of more than one wavelength, for reading RFID tags swiped across the planar surface.

8. The RFID reader of claim 1, wherein the plurality of antenna elements is evenly distributed in an array underneath the planar surface.

9. The RFID reader of claim 1, wherein the network is configured for distributing electromagnetic energy to the antenna elements such that the current phase lag and current amplitudes of the antenna elements such that the radiation beam is pulled away from the center of the antenna array and widened thereby reducing far field gain.

10. A RFID system comprising the RFID reader of claim 1 and a RFID tag, the RFID tag including an antenna and an integrated circuit operable for storing information, the tag antenna operable for receiving energy radiated by the antenna elements of the RFID reader for powering the integrated circuit, the RFID reader operable for transmitting a signal to the RFID tag and for receiving a response to the signal from the RFID tag to recognize information of the RFID tag.

17. The RFID reader of claim 10, wherein the plurality of antenna elements comprise a 3×

3 array of nine patch-antennas such that there are eight perimetric patch-antennas generally about one central patch-antenna that is generally centrally located within the array relative to the eight perimetric antenna elements.

18. The RFID reader of claim 17, wherein the 3×

3 array of patch-antenna is located on a 9 inch×

9 inch ground plane, and wherein the RFID reader is operable as a planar RFID reader at 900 MHz.

11. A passive radio-frequency identification (RFID) reader operable for creating a relatively uniform near field adjacent a planar surface for reading RFID tags above the planar surface, the RFID reader comprising:

a plurality of antenna elements distributed in an array underneath the planar surface, and including;

two or more perimetric antenna elements;

a central antenna element located within the array generally between the perimetric antenna elements;

the two or more perimetric antenna elements being parasitically coupled to the central antenna element, such that a current phase of at least one of the perimetric antenna elements is out of phase with and lagging a current phase of the central antenna element, thereby reducing far field gain.

12. The RFID reader of claim 11, wherein the central antenna element is fed by two or more ports.

13. The RFID reader of claim 11, wherein the central patch-antenna is fed with a voltage of one volt with zero degree delay, and wherein each perimetric patch-antenna is fed parasitically from the central patch-antenna.

14. The RFID reader of claim 13, wherein the perimetric patch-antennas are fed parasitically from the central patch-antenna such that the perimetric patch-antennas are fed with a voltage of 0.25 volts and 100 degree phase delay.

15. The RFID reader of claim 11, wherein one or more feeds are connected only to the central antenna element such that the perimetric antenna elements are parasitically fed from the central patch-antenna without any feed connected to the perimetric antenna elements.

16. The RFID reader of claim 11, wherein the central antenna element is configured with a dual linear polarization, linear polarization, or circular polarization.

19. The RFID reader of claim 11, wherein the perimetric patch-antennas are spaced between one-half wavelength and one wavelength from the central patch-antenna, and wherein the perimetric patch-antennas are approximately one-half wavelength long.

20. The RFID reader of claim 11, wherein the RFID reader does not include a network distributing electromagnetic energy to each of the antenna elements.

21. The RFID reader of claim 11, wherein the plurality of antenna elements comprises an array of five patch-antennas such that there are four perimetric patch-antennas generally about one central patch-antenna that is generally centrally located within the array relative to the four perimetric antenna elements.

22. The RFID reader of claim 21, wherein:

the five patch-antenna array is located on a 9 inch×

9 inch ground plane;

each perimetric patch-antenna is located adjacent a respective corner of the ground plane; and

the central patch-antenna is substantially at the center of the ground plane.

23. The RFID reader of claim 11, wherein the RFID reader is operable for creating a substantially uniform near field adjacent a planar surface having a length of more than one wavelength, for reading RFID tags swiped across the planar surface.

24. The RFID reader of claim 11, wherein the plurality of antenna elements is evenly distributed in an array underneath the planar surface.

25. A RFID system comprising the RFID reader of claim 11 and a RFID tag, the RFID tag including an antenna and an integrated circuit operable for storing information, the tag antenna operable for receiving energy radiated by the antenna elements of the RFID reader for powering the integrated circuit, the RFID reader operable for transmitting a signal to the RFID tag and for receiving a response to the signal from the RFID tag to recognize information of the RFID tag.

26. A passive radio-frequency identification (RFID) reader operable for creating a relatively uniform near field adjacent a planar surface for reading RFID tags generally above the planar surface, the RFID reader comprising:

a first antenna element having a length of about one-half wavelength;

a second antenna element surrounding the first antenna element, and having a perimeter length of about two wavelengths, the second antenna element being parasitically coupled to the first antenna element such that a first order mode is excited on the first antenna element and a second order mode is excited on the second antenna element through the parasitic coupling from the first antenna element.

27. The RFID reader of claim 26, wherein the first antenna element has a dual linear polarization.

28. The RFID reader of claim 26, wherein:

the first antenna element is substantially square; and

the second antenna element includes a substantially square opening in which the first antenna element is positioned such that the second antenna element generally surrounds the first antenna element.

29. The RFID reader of claim 26, wherein a feed is connected only to the first antenna element such that the second antenna element is parasitically fed from the first antenna element without any feed connected to the second antenna element.

30. A RFID system comprising the RFID reader of claim 26 and a RFID tag, the RFID tag including an antenna and an integrated circuit operable for storing information, the tag antenna operable for receiving energy radiated by the antenna elements of the RFID reader for powering the integrated circuit, the RFID reader operable for transmitting a signal to the RFID tag and for receiving a response to the signal from the RFID tag to recognize information of the RFID tag.

31. A method relating to the operation of a passive radio-frequency identification (RFID) reader that includes a plurality of antenna elements distributed in an array generally evenly underneath a planar surface and operable for creating a relatively uniform near field adjacent the planar surface for reading RFID tags generally above the planar surface, the method comprising:

turning on the antenna elements at different times such that a RFID tag above the planar surface is activated from a corresponding one of the antenna elements that is substantially directly underneath the RFID tag at the time the corresponding antenna element is turned on, whereby turning on the antenna elements at different times helps avoid high far field gain.