Microstrip antenna for RFID device

• US 8,564,439 B2
• Filed: 05/27/2010
• Issued: 10/22/2013
• Est. Priority Date: 05/27/2010
• Status: Active Grant

• Current Assignee: University of Kansas
• Original Assignee: University of Kansas
• Inventors: Deavours, Daniel D., Sivakumar, Mutharasu
• Primary Examiner(s): Nguyen, Tai T
• Application Number:
  US12/788,550
• Publication Number:
  US 20110291836A1
• Time in Patent Office: 1,244 Days
• Field of Search: 3405721-5728, 340/5.6, 340/10.51, 343/742, 343/746, 343/764, 343/767, 343/822, 343/860, 343/865
• US Class Current: 340/572.1
• CPC Class Codes: G06K 19/07773 Antenna details antennas for wireless devices, e.g. RFID tags, in general H01Q1/22
• CPC Class Codes: G06K 19/07775 the antenna being on-chip
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/045 with particular feeding means for circular polarisation H01Q9/0428
• CPC Class Codes: H01Q 9/0464 Annular ring patch
• CPC Class Codes: H01Q 9/06 Details

Abstract

Microstrip patch antenna (46), feed structure (48), and matching circuit (50) designs for an RFID tag (10). A balanced feed design using balanced feeds coupled by a shorting stub (56) to create a virtual short between the two feeds so as to eliminate the need for physically connecting the substrate to the ground plane. A dual feed structure design using a four-terminal IC can be connected to two antennas (46a,46b) resonating at different frequencies so as to provide directional and polarization diversity. A combined near-field/far-field design using a microstrip antenna providing electromagnetic coupling for far-field operation, and a looping matching circuit providing inductive coupling for near-field operation. A dual-antenna design using first and second microstrip antennas providing directional diversity when affixed to a cylindrical or conical object, and a protective superstrate (66). An annular antenna (46c) design for application to the top of a metal cylinder around a stem.

Claims

1. A radio frequency identification transponder comprising:

a microstrip patch antenna;

a first feed and a second feed, each feed being coupled with an edge of the microstrip patch antenna; and

a matching circuit coupling the first and second feeds with an integrated circuit.

2. The radio frequency identification transponder of claim 1 wherein the first feed is approximately 180 degrees out of phase with the second feed.

3. The radio frequency identification transponder as set forth in claim 1, wherein the first feed and the second feed are each located an approximately equal distance from and on opposite sides of an approximate center of a non-radiating edge.

4. The radio frequency identification transponder as set forth in claim 1, wherein the first feed and the second feeds each consist of one or more microstrip transmission lines.

5. The radio frequency identification transponder as set forth in claim 1, wherein the matching circuit includes a first transmission line coupled with the first feed and a second transmission line coupled with the second feed, and the first and second transmission lines are substantially symmetrical with respect to an approximate center between the first and second feeds.

6. The radio frequency identification transponder as set forth in claim 5, wherein the first transmission line and the second transmission line are coupled with the integrated circuit.

7. The radio frequency identification transponder as set forth in claim 1, wherein the matching circuit consists of a first transmission line coupled with the first feed and a second transmission line coupled with the second feed, and the first and second transmission lines are substantially symmetrical with respect to an approximate center between the first and second feeds.

8. The radio frequency identification transponder as set forth in claim 1, wherein the matching circuit includes a transmission line coupling the first feed with the second feed and creating a virtual short between the feeds.

9. In a radio frequency identification transponder for physical association with an object and for storing and communicating data regarding the object, the radio frequency identification transponder having a microstrip patch antenna and an integrated circuit, the transponder further comprising:

a first feed and a second feed, each feed being coupled with an edge of the microstrip patch antenna; and

a matching circuit coupling the first and second feeds with the integrated circuit.

10. The radio frequency identification transponder as set forth in claim 9, wherein the first feed is approximately 180 degrees out of phase with the second feed.

11. The radio frequency identification transponder as set forth in claim 10, wherein the matching circuit includes a transmission line coupling the first feed with the second feed and creating a virtual short between the feeds.

12. The radio frequency identification transponder as set forth in claim 11, wherein the first feed and the second feed are each located an approximately equal distance from and on opposite sides of an approximate center of a non-radiating edge.

13. The radio frequency identification transponder as set forth in claim 11, wherein the first fee and the second feed each consists of one or more microstrip transmission lines.

14. The radio frequency identification transponder as set forth in claim 11, wherein the matching circuit consists of a first transmission line coupled with the first feed and a second transmission line coupled with the second feed, and the first and second transmission lines are substantially symmetrical with respect to an approximate center between the first and second feeds.

15. A radio frequency identification transponder comprising:

a first patch antenna and a second patch antenna;

an integrated circuit having a first pair of terminals and a second pair of terminals; and

a first matching circuit for coupling the first patch antenna to the first pair of terminals; and

a second matching circuit for coupling the second patch antenna to the second pair of terminals.

16. The radio frequency identification transponder as set forth in claim 15, wherein the first matching circuit resonates at a first frequency, and the second matching circuit resonates at a second frequency.

17. The radio frequency identification transponder as set forth in claim 15, further including, for each patch antenna, first and second balanced feeds and a shorting stub coupling the balanced feeds.

18. The radio frequency identification transponder as set forth in claim 15, wherein the first patch antenna is a microstrip patch antenna operable above a ground plane separated by a substrate.

19. The radio frequency identification transponder as set forth in claim 18, wherein the second patch antenna is operable with the substrate in free space.

20. The radio frequency identification transponder as set forth in claim 16, wherein the first frequency is approximately identical to the second frequency.

21. In a radio frequency identification transponder for physical association with an object and for storing and communicating data regarding the object, the transponder further comprising:

a first patch antenna and a second patch antenna; and

an integrated circuit having a first pair of terminals and a second pair of terminals;

wherein the first pair of terminals is coupled to the first patch antenna, and the second pair of terminals is coupled to the second patch antenna.

22. The radio frequency identification transponder as set forth in claim 21 further comprising:

a first matching circuit for coupling the first patch antenna to the first pair of terminals; and

a second matching circuit for coupling the second patch antenna to the second pair of terminals.

23. The radio frequency identification transponder as set forth in claim 22, wherein the first matching circuit resonates at a first frequency, and a second matching circuit resonates at a second frequency.

24. The radio frequency identification transponder as set forth in claim 21 further including, for each patch antenna, first and second balanced feeds.

25. The radio frequency identification transponder as set forth in claim 24 further including a shorting stub coupling the balanced feeds.

26. The radio frequency identification transponder as set forth in claim 21, wherein the first patch antenna is a microstrip path antenna operable above a ground plane separated by a substrate.

27. The radio frequency identification transponder as set forth in claim 26, wherein the second patch antenna is operable with the substrate in free space.

28. The radio frequency identification transponder as set forth in claim 23, wherein the first frequency is approximately identical to the second frequency.

29. A radio frequency identification transponder comprising:

a microstrip patch antenna having an annular shape with an inner edge and an outer edge;

an integrated circuit;

a first feed and a second feed, each feed being coupled with either edge of the microstrip patch antenna; and

a matching circuit coupling the first and second feeds with the integrated circuit.

30. The radio frequency identification transponder of claim 29, wherein the first feed is approximately 180 degrees out of phase with the second feed.

31. The radio frequency identification transponder of claim 29, wherein the matching circuit further includes a transmission line coupling the first feed with the second feed and creates a virtual short between the feeds.

32. The radio frequency identification transponder as set forth in claim 29, wherein the matching circuit is coupled with the inner edge of the microstrip patch antenna.

33. The radio frequency identification transponder as set forth in claim 29, wherein the matching circuit is coupled with the outer edge of the microstrip patch antenna.

34. The radio frequency identification transponder as set forth in claim 29, wherein the microstrip antenna has an annular polygonal shape.

35. The radio frequency identification transponder as set forth in claim 34, further including one or more slots manufactured into the annular polygonal shape.

36. In a radio frequency identification transponder for physical association with a cylindrical object having a stem and for storing and communicating data regarding the object, the radio frequency identification transponder having a microstrip patch antenna and an integrated circuit, the transponder further comprising:

the microstrip patch antenna having an annular shape with an inner edge and an outer edge;

a first feed and a second feed, each feed being coupled to the microstrip patch antenna, and the first feed being approximately 180 degrees out of phase with the second feed; and

a matching circuit coupling the first and second feeds with the integrated circuit.

37. The radio frequency identification transponder as set forth in claim 36, wherein each feed is coupled with either edge of the microstrip patch antenna.

38. The radio frequency identification transponder as set forth in claim 36, wherein the matching circuit includes a transmission line coupling the first feed with the second feed and creates a virtual short between the feeds.

39. The radio frequency identification transponder as set forth in claim 36, wherein the matching circuit is coupled with the inner edge of the microstrip patch antenna.

40. The radio frequency identification transponder as set forth in claim 36, wherein the matching circuit is coupled with the outer edge of the microstrip patch antenna.

41. The radio frequency identification transponder as set forth in claim 36, wherein the microstrip patch antenna has an annular polygonal shape.

42. The radio frequency identification transponder as set forth in claim 41, further including one or more slots manufactured into the annular shape.