Low return loss rugged RFID antenna

• US 20070096919A1
• Filed: 11/03/2005
• Published: 05/03/2007
• Est. Priority Date: 11/03/2005
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Duron, Mark, Knadle, Richard
• Granted Patent: US 7,551,140 B2
• Time in Patent Office: Days
• US Class Current: 340/572.8
• CPC Class Codes: B66F 9/0755 Position control; Position detectors
• 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: G06K 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 9/0435 using two feed points

Abstract

Methods, systems, and apparatuses for RFID devices, such as reader antennas, are described. A reader antenna includes a quadrature hybrid coupler, a termination element, and an antenna, such as a patch antenna. The quadrature hybrid coupler has first, second, third, and fourth ports. The first port receives an input radio frequency RF signal. The second port outputs a first RF output signal. The third port outputs a second RF output signal. The second RF output signal is shifted in phase by 90 degrees relative to the first RF output signal. The fourth port is coupled to the termination element. The patch antenna has a first point coupled to the first RF output signal and a second point coupled to the second RF output signal. The patch antenna radiates a circularly polarized RF signal due to the received first and second RF output signals. The circularly polarized RF signal may be used to interrogate tags. Furthermore, the reader antenna is integrated into a ruggedized structure that provides environmental protection for the antenna, including providing shock absorption for impacts to the antenna.

Claims

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

a quadrature hybrid coupler having first, second, third, and fourth ports, wherein the first port receives an input radio frequency (RF) signal, the second port outputs a first RF output signal, and the third port outputs a second RF output signal, wherein the second RF output signal is shifted in phase by 90 degrees relative to the first RF output signal;

a termination element coupled to the fourth port; and

a patch antenna having a first point coupled to the first RF output signal and a second point coupled to the second RF output signal, wherein the patch antenna radiates a circularly polarized RF signal.

2. The device of claim 1, further comprising:

a circuit board, wherein the termination element and quadrature hybrid coupler are mounted to the circuit board.

3. The device of claim 2, wherein the input RF signal and the first and second RF output signals are routed on the circuit board as printed circuit transmission lines.

4. The device of claim 3, wherein the printed circuit transmission lines are coplanar waveguide type transmission lines.

5. The device of claim 2, wherein the patch antenna is planar and is positioned parallel to the circuit board.

6. The device of claim 5, wherein the first output RF signal is coupled to the first point of the patch antenna by a first compressible contact member mounted between the circuit board and the first point of the patch antenna;

and

wherein the second output RF signal is coupled to the second point of the patch antenna by a second compressible contact member mounted between the circuit board and the second point of the patch antenna.

7. The device of claim 6, wherein the first and second compressible contact members are pogo pins.

8. The device of claim 6, wherein the first and second compressible contact members are conductive elastomer contacts.

9. The device of claim 5, further comprising:

a back plate having a centrally-located opening, wherein the circuit board is mounted in the centrally-located opening.

10. The device of claim 9, further comprising:

a compressible electrically insulating material that supports the patch antenna on the back plate.

11. The device of claim 10, wherein the compressible electrically insulating material is a silicone rubber dielectric material.

12. The device of claim 11, wherein the silicone rubber dielectric material is a high durometer silicone rubber.

13. The device of claim 10, wherein the compressible electrically insulating material provides for shock absorption during an impact on the patch antenna.

14. The device of claim 10, wherein the compressible electrically insulating material has a second centrally located opening to form an open space between the circuit board and patch antenna.

15. The device of claim 10, wherein the compressible electrically insulating material covers a surface of the circuit board to substantially fill a space between the circuit board and patch antenna.

16. The device of claim 9, wherein a perimeter edge of the circuit board is attached to a perimeter edge of the centrally-located opening by an adhesive.

17. The device of claim 9, wherein the circuit board is mounted in the centrally-located opening by a plurality of attachment elements.

18. The device of claim 9, wherein the back plate is coupled to ground.

19. The device of claim 1, wherein a signal reflected from the first point of the patch antenna enters the second port of the quadrature hybrid coupler and is split into first and second reflection signals, wherein the second reflection signal is shifted in phase by 90 degrees relative to the first reflection signal;

wherein a signal reflected from the second point of the patch antenna enters the third port of the quadrature hybrid coupler and is split into third and fourth reflection signals by the quadrature hybrid coupler, wherein the fourth reflection signal is shifted in phase by 90 degrees relative to the third reflection signal;

wherein the first and third reflection signals cancel each other at the first port of the quadrature hybrid coupler; and

wherein the second and fourth reflection signals are received by the termination element coupled to the fourth port of the quadrature hybrid coupler.

20. The device of claim 1, wherein the termination element is a resistor.

21. The device of claim 1, wherein the quadrature hybrid coupler is a directional quadrature hybrid coupler.

22. A radio frequency identification (RFID) device, comprising:

a back plate;

a circuit board supported by the back plate, wherein the circuit board receives an input radio frequency (RF) signal and outputs a first RF output signal and a second RF output signal;

a patch antenna;

a compressible electrically insulating material that mounts the patch antenna on the back plate;

a first compressible contact member that couples the first output RF signal to a first point of the patch antenna; and

a second compressible contact member that couples the second output RF signal to a second point of the patch antenna.

23. The device of claim 22, wherein the back plate has a centrally-located opening, wherein the circuit board is mounted in the centrally-located opening.

24. The device of claim 23, wherein a perimeter edge of the circuit board is attached to a perimeter edge of the centrally-located opening by an adhesive.

25. The device of claim 23, wherein the circuit board is mounted in the centrally-located opening by a plurality of attachment elements.

26. The device of claim 22, wherein the compressible electrically insulating material is a silicone dielectric material.

27. The device of claim 26, wherein the silicone dielectric material is a high durometer silicone rubber.

28. The device of claim 22, wherein the compressible electrically insulating material provides for shock absorption during an impact on the patch antenna.

29. The device of claim 22, wherein the compressible electrically insulating material has a centrally located opening to form an open space between the circuit board and patch antenna.

30. The device of claim 22, wherein the compressible electrically insulating material covers a surface of the circuit board to substantially fill a space between the circuit board and patch antenna.

31. The device of claim 22, wherein the back plate is coupled to ground.

32. The device of claim 22, further comprising:

a quadrature hybrid coupler mounted to the circuit board, and having first, second, third, and fourth ports, wherein the first port receives the input radio frequency (RF) signal, the second port outputs the first RF output signal, and the third port outputs the second RF output signal, wherein the second RF output signal is shifted in phase by 90 degrees relative to the first RF output signal; and

a termination element mounted to the circuit board and coupled to the fourth port.

33. The device of claim 32, wherein the patch antenna radiates a circularly polarized RF signal.

34. The device of claim 22, further comprising:

a plurality of tuning screws positioned in openings through the back plate having tips positioned adjacent to the patch antenna.

35. The device of claim 34, wherein the tuning screws can be adjusted to tune at least one parameter of the patch antenna.

36. The device of claim 22, wherein the quadrature hybrid coupler is a directional quadrature hybrid coupler.

37. The device of claim 22, further comprising:

a RFID reader that generates the input RF signal.

38. The device of claim 37, wherein the RFID reader comprises a battery and a wireless communications module.

39. The device of claim 38, wherein the device is mounted to a forklift.

40. The device of claim 39, wherein the device is mounted to the forklift between forks of the forklift.

41. The device of claim 22, further comprising:

a frame attached to the compressible electrically insulating material, wherein the frame surrounds a perimeter edge of the patch antenna.

42. A method for transmitting a radio frequency (RF) signal, comprising:

receiving a RF signal on a transmission line;

generating a first RF output signal and a second RF output signal from the received RF signal using a quadrature hybrid coupler, wherein the second RF output signal is shifted in phase by 90 degrees relative to the first RF output signal;

coupling the first RF output signal to a first point on a patch antenna;

coupling the second RF output signal to a second point on the patch antenna; and

radiating a circularly polarized RF signal from the patch antenna.

43. The method of claim 42, wherein said generating comprises:

receiving the RF signal at a first port of the quadrature hybrid coupler;

outputting the first RF output signal at a second port of the quadrature hybrid coupler; and

outputting the second RF output signal at a third port of the quadrature hybrid coupler.

44. The method of claim 43, further comprising:

receiving a signal reflected from the first point of the patch antenna at the second port of the quadrature hybrid coupler;

splitting the signal reflected from the first point into first and second reflection signals, wherein the second reflection signal is shifted in phase by 90 degrees relative to the first reflection signal;

receiving a signal reflected from the second point of the patch antenna at the third port of the quadrature hybrid coupler;

splitting the signal reflected from the second point into third and fourth reflection signals, wherein the third reflection signal is shifted in phase by 90 degrees relative to the fourth reflection signal;

causing the first and third reflection signals to cancel each other at the first port of the quadrature hybrid coupler; and

receiving the second and fourth reflection signals at a termination element coupled to a fourth port of the quadrature hybrid coupler.

45. The method of claim 42, further comprising:

tuning at least one parameter of the patch antenna.

46. The method of claim 45, wherein said tuning comprises:

tuning one or more of a horizontal resonant frequency, a vertical resonant frequency, horizontal and vertical impedance tracking, or horizontal to vertical isolation.

47. The method of claim 42, further comprising:

selecting the quadrature hybrid coupler to be a printed circuit board mountable quadrature hybrid coupler.

48. The method of claim 45, wherein said tuning increases an accuracy of amplitude matching and a 90 degree phase difference accuracy between the first and second RF output signals.

49. The method of claim 45, wherein said tuning comprises:

causing the patch antenna to exhibit an absolute return loss of −

30 dB or greater.

50. The method of claim 45, wherein said tuning comprises:

improving an axial ratio.