ASYMMETRIC RFID TAG ANTENNA

• US 20070279231A1
• Filed: 06/01/2007
• Published: 12/06/2007
• Est. Priority Date: 06/05/2006
• Status: Abandoned Application

• Current Assignee: Shenloon Kip Assets LLC (Intellectual Ventures LLC)
• Original Assignee: Hong Kong University of Science and Technology
• Inventors: Cheng, Chi Ho, Murch, Ross
• Application Number:
  US11/756,773
• Publication Number:
  US 20070279231A1
• Time in Patent Office: Days
• US Class Current: 340/572.700
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• 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 9/16 with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole H01Q9/44 takes precedence
• CPC Class Codes: H01Q 9/26 with folded element or elements, the folded parts being spaced apart a small fraction of operating wavelength resonant loop antennas H01Q7/00

Abstract

The invention provides an asymmetric UHF RFID tag antenna that variously comprises a capacitive load, a folded loop conductor and an inductive matching element, which provides a differential input for RFID tag circuitry. The design provides a small form factor while maintaining a high gain and impedance tuning properties. Various refinements and associated devices and systems using the design are provided and disclosed according to a host of optional embodiments.

Claims

1. A radio frequency identification (RFID) antenna for use with radio waves of a nominal wavelength, the RFID antenna comprising:

a first antenna arm comprising a variable dimension capacitive load having a first tunable RFID antenna dimension and a second tunable RFID antenna dimension, wherein the second tunable RFID antenna dimension corresponds to a RFID antenna width;

a second antenna arm comprising a folded conductor and an inductive matching stub;

wherein the folded conductor forms a closed loop with the capacitive load of the first antenna arm;

wherein a position of the inductive matching stub corresponds to a third tunable RFID antenna dimension;

wherein the third tunable RFID antenna dimension is selected to cause resonance with a selected capacitance corresponding to a capacitance of RFID tag circuitry to be used with the RFID antenna; and

wherein the first and second antenna arms are arranged to provide a greatest RFID antenna dimension of less than one quarter of the nominal wavelength of the radio waves to be used.

2. The RFID antenna of claim 1, wherein an input impedance of the RFID antenna is set such that the RFID antenna has a conjugate matching with the RFID tag circuitry, resulting in substantially optimal power transfer to a RFID tag.

3. The RFID antenna of claim 1, wherein the nominal wavelength of the radio waves substantially corresponds to the 2.4 Gigahertz (GHz) Industrial, Scientific and Medical (ISM) band.

4. The RFID antenna of claim 1, wherein the nominal wavelength of the radio waves substantially corresponds to the 900 Megahertz (MHz) Industrial, Scientific and Medical (ISM) band.

5. The RFID antenna of claim 1, wherein the RFID antenna comprises a conducting pattern substantially constructed of copper and supported by a substrate.

6. The RFID antenna of claim 3, wherein the second and third tunable RFID antenna dimensions are about 10 millimeters and 20 millimeters, respectively.

7. The RFID antenna of claim 4, wherein the second and third tunable RFID antenna dimensions are about 30 millimeters and 60 millimeters, respectively.

8. The RFID antenna of claim 1, wherein the RFID antenna is substantially impedance matched to the RFID tag circuitry by adjusting at least one of the first, second, and third tunable RFID antenna dimensions.

9. A RFID tag comprising a RFID application specific integrated circuit (ASIC) for communicatively coupling to the RFID antenna of claim 1.

10. A radio frequency identification (RFID) tag system comprising:

a RFID antenna;

RFID tag circuitry, wherein the RFID tag circuitry is at least operable to receive signals from the RFID antenna;

wherein the RFID antenna further comprises;

a first antenna element comprising a capacitive load with first and second antenna dimensions, wherein the second antenna dimension corresponds to RFID antenna width;

a second antenna element comprising a folded conductor and an inductive matching element, wherein the folded conductor forms a closed loop with the capacitive load;

wherein a location of the inductive matching element relative to the first and second antenna elements corresponds to a third antenna dimension;

wherein the third antenna dimension is adjustable to resonate with a capacitance of the RFID tag circuitry;

wherein the RFID antenna is substantially impedance matched to the RFID tag circuitry by, at least, adjusting one or more of the first, second, and third antenna dimensions.

11. The RFID tag system of claim 10, wherein the first and second antenna elements are arranged to provide a greatest RFID antenna dimension of less than one quarter of a nominal operating wavelength of the RFID tag circuitry.

12. The RFID tag system of claim 10, further comprising:

a RFID tag reader communicatively coupled to the RFID antenna and configured to send and receive radio frequency energy equivalent to a nominal operating wavelength of the RFID tag circuitry.

13. The RFID tag system of claim 10, wherein the RFID tag circuitry has impedance equivalent to 10−

j200 ohms.

14. The RFID tag system of claim 11, wherein an operating wavelength of the RFID tag circuitry substantially corresponds to one of a 900 Megahertz (MHz) Industrial, Scientific and Medical (ISM) band and a 2.4 Gigahertz (GHz) Industrial, Scientific and Medical (ISM) band.

15. A method of manufacturing a radio frequency identification (RFID) antenna on a nonconductive substrate defined by an X-Y plane, the method comprising:

determining a RFID tag circuitry capacitance, impedance, and nominal operating wavelength;

selecting a capacitive load to be formed on the substrate having X-Y plane dimensions corresponding to first and second RFID antenna dimensions and that is selected to resonate with the determined RFID tag circuitry capacitance;

selecting an inductive matching stub location on the substrate, wherein the inductive matching stub location in the X-Y plane corresponds to a third RFID antenna dimension;

selecting a conductor length to be formed on the substrate adjacent to the inductive matching stub;

adjusting, at least, one or more of the first, second, and third RFID antenna dimensions to substantially match the RFID antenna impedance with the RFID tag circuitry impedance; and

forming on the substrate the conductor length, the inductive matching stub, and the capacitive load such that a closed loop is formed thereby, wherein the longest RFID antenna dimension is less than one quarter wavelength of the RFID tag circuitry operating wavelength.

16. The method of claim 15, the forming step further comprising:

forming the conductor length into a folded configuration to minimize the longest RFID antenna dimension.

17. The method of claim 15, the determining step further comprising:

determining the operating wavelength to correspond to the 900 Megahertz (MHz) Industrial, Scientific and Medical (ISM) band.

18. The method of claim 15, the determining step further comprising:

determining the operating wavelength to correspond to the 2.4 Gigahertz (GHz) Industrial, Scientific and Medical (ISM) band.

19. The method of claim 15, the forming step further comprising:

forming one or more of the conductor length, the inductive matching stub, and the capacitive load substantially from copper.

20. The method of claim 15, the determining step further comprising:

determining the RFID tag circuitry impedance to be equivalent to 10−

j200 ohms.

21. An asymmetric radio frequency identification (RFID) tag antenna comprising:

a polygon-shaped capacitive load;

a folded arm that forms a closed loop with the polygon-shaped load, the folded arm having an inductive matching stub that is used to resonate with a capacitance of a chip tag, the loop having a length; and

a location for receiving the chip tag.

22. The antenna of claim 21, wherein the antenna is an ultra high frequency (UHF) tag antenna.

23. The antenna of claim 21, wherein the antenna is an antenna for a passive RFID tag.

24. The antenna of claim 21, wherein the polygon-shaped capacitive load is rectangular.

25. The antenna of claim 21, wherein the length of the loop is determined based on a function of a kind of backing material of the antenna.

26. The antenna of claim 25, wherein the kind of backing material includes one or more of cardboard, metal, plastic, cloth, ceramic, or glass.

27. The antenna of claim 21, wherein the length of the loop is determined based on proximity to a high dielectric material.

28. The antenna of claim 21, wherein the length is no greater than one quarter of an operating wavelength of the antenna.