Discontinuous-Loop RFID Reader Antenna And Methods

• US 20080048867A1
• Filed: 01/16/2007
• Published: 02/28/2008
• Est. Priority Date: 01/18/2006
• Status: Abandoned Application

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Oliver, Ronald A., Kavounas, Gregory T.
• Application Number:
  US11/623,403
• Publication Number:
  US 20080048867A1
• Time in Patent Office: Days
• US Class Current: 340/572.7
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

RFID reader antennas and methods for generating magnetic fields. An antenna can be made from conductors that do not contact each other, but have loop portions spatially arranged along a loop section. The loop portions have gaps between them, and thus the loop section is discontinuous. The loop section can be driven from near its ends by a UHF RFID excitation signal, which travels through the loop portions, and also through the gaps because it is AC. Thus an excitation current becomes established along the loop section, which generates a useable magnetic field. Each loop portion can be short, so that the magnetic field it contributes will not self-cancel due to the shorter wavelength of UHF RFID. The loop section can be large independently of the wavelength, so that the magnetic field is of a size large enough to be useful for ILT in RFID.

Claims

1. An antenna for use with a Radio Frequency Identification (RFID) reader system that outputs as a potential difference between a first driving node and a second driving node an excitation signal alternating at an excitation frequency larger than 200 MHz, the antenna for generating wireless fields responsive to receiving the excitation signal for communicating with an RFID tag, the antenna comprising:

a first conductor coupled to receive at a first driving point the excitation signal from the first driving node;

a second conductor coupled to receive at a second driving point the excitation signal from the second driving node; and

a third conductor, and

in which

the first, the second, and the third conductors do not contact each other, and include respective loop portions that are spatially arranged along a loop section that starts from the first driving point and ends at the second driving point, the loop portions being separated by gaps along the loop section,

the third conductor is coupled to receive the excitation signal across the gaps from the first conductor and from the second conductor, and

responsive to thus receiving the excitation signal, an excitation current becomes established along the loop portions of the first, the second, and the third conductors, the excitation current thereby generating the wireless fields.

2. The antenna of claim 1, in which

the excitation frequency is in a range centered around approximately 900 MHz.

3. The antenna of claim 1, in which

the excitation frequency is in a range centered around approximately 2.4 GHz.

4. The antenna of claim 1, in which

the first driving point is arranged to come in contact with the first driving node to receive the excitation signal.

5. The antenna of claim 1, in which

the first driving point is coupled to receive the excitation signal from the first driving node inductively across a gap.

6. The antenna of claim 1, in which

the loop section is substantially circularly shaped.

7. The antenna of claim 1, in which

the loop section is substantially elliptically shaped.

8. The antenna of claim 1, in which

the loop section is substantially rectangularly shaped.

9. The antenna of claim 1, further comprising:

a fourth conductor not contacting any of the first, the second, and the third conductors, the fourth conductor having an elongate loop portion along the loop section, the loop portion of the fourth conductor separated from the loop portions of the second conductor and the third conductor by gaps along the loop section, the loop portion of the fourth conductor being thus coupled to receive the excitation signal inductively only from the third conductor and from the second conductor such that the excitation current becomes established along the loop portion of also the fourth conductor.

10. The antenna of claim 1, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor is elongate and has a length smaller than λ

/4.

11. The antenna of claim 1, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor is elongate and has a length smaller than λ

/8.

12. The antenna of claim 1, in which

the excitation frequency defines a wavelength λ

, and

the loop section has a length larger than λ

.

13. The antenna of claim 1, further shaped such that

the loop portion of the third conductor is substantially elongate and has a shape that introduces a phase lag in the propagation of the excitation current being received from the first conductor,

a gap between the third conductor and the second conductor has a shape that introduces a phase lead in the propagation of the excitation current from the third conductor to the second conductor, and

the lead substantially cancels the lag.

14. The antenna of claim 1, in which

the loop portions of the first, the second, and the third conductors are substantially elongate and have substantially similar lengths.

15. The antenna of claim 1, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that are shaped with square-like corners.

16. The antenna of claim 1, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that have slanted shapes.

17. The antenna of claim 1, in which

the loop section is disposed within a single plane.

18. The antenna of claim 17, in which

the excitation current established along the loop portion of the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tag is primarily the magnetic subfield at a location where it has a direction perpendicular to the plane.

19. The antenna of claim 17, in which

the excitation current carried in the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tag is primarily the magnetic subfield at a location where it has a direction parallel to the plane.

20. The antenna of claim 1, in which

the loop section is not disposed within a single plane.

21. The antenna of claim 1, further comprising:

a plurality of conductors arranged along a second loop section.

22. The antenna of claim 21, in which

the second loop section is excited by the first and the second driving node.

23. The antenna of claim 21, in which

no conductors are shared by the two loop sections.

24. The antenna of claim 21, in which

some conductors are shared by the two loop sections.

25. The antenna of claim 1, further comprising:

a plurality of additional conductors not contacting any of each other, the first, the second, and the third conductors, the additional conductors having respective elongate loop portions along the loop section that are separated by gaps along the loop section, and

in which the additional conductors are coupled so receive the excitation signal inductively only across some of the gaps from the first conductor and from the second conductor such that the excitation current becomes established along the loop portions of also the additional conductors.

26. The antenna of claim 25, in which

the loop section is disposed within a single plane.

27. The antenna of claim 25, in which

the loop section is not disposed within a single plane.

28. The antenna of claim 25, in which

the loop portions of all of the additional conductors are spatially arranged along the loop section in a single row.

29. The antenna of claim 25, in which

the additional conductors are at least 7 in number.

30. The antenna of claim 25, in which

at least three of the additional conductors have shapes that are substantially similar with each other.

31. The antenna of claim 30, in which

the three of the additional conductors are adjacent to each other, and separated by two gaps with shapes that are substantially similar with each other.

32. The antenna of claim 25, in which

the loop portions of at least three of the additional conductors are substantially elongate, and spatially arranged along the loop section in a first row, and

the loop portions of at least another three of the additional conductors are spatially arranged along the loop section in a second row that substantially surrounds the first row.

33. The antenna of claim 32, in which

at least some of the loop portions of the additional conductors are elongate and have a total length more than 120% of a length of the loop section.

34. The antenna of claim 32, in which

at least three more of the loop portions of the additional conductors are spatially arranged along the loop section in a third row that substantially surrounds the first row and the second row.

35. The antenna of claim 34, in which

at least some of the loop portions of the additional conductors are elongate and have a total length more than twice a length of the loop section.

36. A method for a Radio Frequency Identification (RFID) reader system to communicate with Radio Frequency Identification (RFID) tags, the system including a coupled antenna having at least a first, a second, and a third non-contacting conductors, the first, the second, and the third conductors including respective loop portions that are spatially arranged along a loop section that starts from a first driving point of the first conductor and ends at a second driving point of the second conductor, the loop portions being separated by gaps along the loop section, the method comprising:

outputting from the system an excitation signal alternating at an excitation frequency larger than 200 MHz such that the excitation signal is coupled to the first driving point and to the second driving point, the excitation signal thereby being coupled inductively only also to the third conductor, and an excitation current thereby becoming established along the loop portions of the first, the second, and the third conductors, the excitation current thereby generating wireless fields for communicating with the RFID tags.

37. The method of claim 36, in which

the excitation frequency is in a range centered around approximately 900 MHz.

38. The method of claim 36, in which

the excitation frequency is in a range centered around approximately 2.4 GHz.

39. The method of claim 36, in which

the excitation signal is coupled to the first driving point by bringing a first driving node of the system in contact with the first driving point.

40. The method of claim 36, in which

the excitation signal is coupled to the first driving point inductively across a gap.

41. The method of claim 36, in which

the loop section is substantially circularly shaped.

42. The method of claim 36, in which

the loop section is substantially elliptically shaped.

43. The method of claim 36, in which

the loop section is substantially rectangularly shaped.

44. The method of claim 36, in which

the antenna has a fourth conductor not contacting any of the first, the second, and the third conductors, the fourth conductor having an elongate loop portion along the loop section, the loop portion of the fourth conductor separated from the loop portions of the second conductor and the third conductor by gaps along the loop section, and

the excitation current becomes established along the loop portions of also the fourth conductor.

45. The method of claim 36, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor has a length smaller than λ

/4.

46. The method of claim 36, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor has a length smaller than λ

/8.

47. The method of claim 36, in which

the excitation frequency defines a wavelength λ

, and

the loop section has a length larger than λ

.

48. The method of claim 36, in which

the antenna is further shaped such that

the loop portion of the third conductor is elongate and has a shape that introduces a phase lag in the propagation of the excitation current being received from the first conductor,

a gap between the third conductor and the second conductor has a shape that introduces a phase lead in the propagation of the excitation current from the third conductor to the second conductor, and

the phase lead substantially cancels the phase lag.

49. The method of claim 36, in which

the loop portions of the first, the second, and the third conductors are substantially elongate and have substantially similar lengths.

50. The method of claim 36, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that are shaped with square-like corners.

51. The method of claim 36, in which

the loop section is disposed within a single plane.

52. The method of claim 51, in which

the excitation current established along the loop portion of the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tags is primarily the magnetic subfield at a location where it has a direction perpendicular to the plane.

53. The method of claim 51, in which

the excitation current established along the loop portion of the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tags is primarily the magnetic subfield at a location where it has a direction parallel to the plane.

54. The method of claim 36, in which

the loop section is not disposed within a single plane.

55. An antenna for use with a Radio Frequency Identification (RFID) reader system that outputs as a potential difference between a first driving node and a second driving node an excitation signal alternating at an excitation frequency larger than 200 MHz, the antenna for generating wireless fields responsive to receiving the excitation signal for communicating with an RFID tag, the antenna comprising:

a first conductor coupled to receive at a first driving point the excitation signal from the first driving node;

a second conductor coupled to receive at a second driving point the excitation signal from the second driving node;

a third conductor coupled to receive at a third driving point the excitation signal from the first driving node; and

a fourth conductor coupled to receive at a fourth driving point the excitation signal from the second driving node;

in which

the first, the second, the third, and the fourth conductors do not contact each other and include respective loop portions,

the loop portions of the first conductor and of the second conductor are spatially arranged along a first loop section that starts from the first driving point and ends at the second driving point, and are separated by a first gap along the first loop section,

the loop portions of the third conductor and of the fourth conductor are spatially arranged along a second loop section that starts from the third driving point and ends at the fourth driving point, and are separated by a second gap along the second loop section, and

responsive to thus receiving the excitation signal, a first excitation current becomes established that has a non-zero magnitude along the entire first loop section, and a second excitation current becomes established that has a non-zero magnitude along the entire second loop section, the first and the second excitation currents thereby generating the wireless fields.

56. The antenna of claim 55, in which

the excitation frequency is in a range centered around approximately 900 MHz.

57. The antenna of claim 55, in which

the excitation frequency is in a range centered around approximately 2.4 GHz.

58. The antenna of claim 55, in which

the first driving point is arranged to come in contact with the first driving node to receive the excitation signal.

59. The antenna of claim 55, in which

the first driving point is coupled to receive the excitation signal from the first driving node inductively across a gap.

60. The antenna of claim 55, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like a circle.

61. The antenna of claim 55, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like an ellipse.

62. The antenna of claim 55, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like a rectangle.

63. The antenna of claim 55, further comprising:

a fifth conductor not contacting any of the tint, the second, the third, and the fourth conductors, the fifth conductor having an elongate loop portion along the first loop section, the loop portion of the fifth conductor separated from the loop portions of the first conductor and the second conductor by gaps along the first loop section, the loop portion of the fifth conductor being thus coupled to receive the excitation signal inductively only from the first conductor and from the second conductor such that the first excitation current becomes established along the loop portion of also the fifth conductor.

64. The antenna of claim 55, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor in elongate and has a length smaller than λ

/4.

65. The antenna of claim 55, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor is elongate and has a length smaller than λ

/8.

66. The antenna of claim 55, in which

the excitation frequency defines a wavelength λ

, and

the first loop section has a length larger than λ

.

67. The antenna of claim 55, in which

the loop portions of the first, the second, and the third conductors are substantially elongate and have substantially similar lengths.

68. The antenna of claim 55, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that are shaped with square-like corners.

69. The antenna of claim 55, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that have slanted shapes.

70. The antenna of claim 55, in which

the first and the second loop sections are disposed within a single plane.

71. The antenna of claim 70, in which

the excitation current established along the loop portion of the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tag is primarily the magnetic subfield at a location where it has a direction perpendicular to the plane.

72. The antenna of claim 70, in which

the excitation current established along the loop portion of the third conductor generates a magnetic subfield around the third conductor, and

the wireless field for communication with the RFID tag is primarily the magnetic subfield at a location where it has a direction parallel to the plane.

73. The antenna of claim 55, in which

the loop portions of the first, the second, the third and the fourth conductors are elongate and have substantially similar lengths.

74. The antenna of claim 55, in which

the loop portion of the third conductor is elongate and terminates in two ends that are shaped with square-like corners.

75. The antenna of claim 55, further comprising;

a plurality of conductors arranged along a third loop section.

76. The antenna of claim 75, in which

the third loop section is excited by the first and the second driving node.

77. A method for a Radio Frequency Identification (RFID) reader system to communicate with Radio Frequency Identification (RFID) tags, the system including a coupled antenna having at least a first, a second, a third, and a fourth non-contacting conductors, the loop portions of the first conductor and of the second conductor being spatially arranged along a first loop section that starts from a first driving point of the first conductor and ends at a second driving point of the second conductor, and being separated by a first gap along the first loop section, the loop portions of the third conductor and of the fourth conductor being spatially arranged along a second loop section that starts from a third driving point of the third conductor and ends at a fourth driving point of the fourth conductor, and being separated by a second gap along the second loop section, the method comprising:

outputting from the system an excitation signal alternating at an excitation frequency larger than 200 MHz such that the excitation signal is coupled to the first, the second, the third, and the fourth driving points, a first excitation current thereby becoming established that has a non-zero magnitude along the entire first loop section, and a second excitation current becoming established that has a non-zero magnitude along the entire second loop section, the first and the second excitation currents thereby generating wireless fields for communicating with the RFID tags.

78. The method of claim 77, in which

the excitation frequency is in a range centered around approximately 900 MHz.

79. The method of claim 77, in which

the excitation frequency is in a range centered around approximately 2.4 GHz.

80. The method of claim 77, in which

the excitation signal is output as a potential difference between a first driving node and a second driving node,

the first driving node is coupled to the first driving point and to the third driving point, and

the second driving node is coupled to the third driving point and to the fourth driving point.

81. The method of claim 80, in which

the first driving node is coupled to the first driving point by being in contact with it.

82. The method of claim 80, in which

the first driving node is coupled to the first driving point inductively across a gap.

83. The method of claim 77, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like a circle.

84. The method of claim 77, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like an ellipse.

85. The method of claim 77, in which

the first loop section and the second loop section, taken together, form a shape that is substantially like a rectangular.

86. The method of claim 77, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor is elongate and has a length smaller than λ

/4.

87. The method of claim 77, in which

the excitation frequency defines a wavelength λ

, and

the loop portion of the third conductor is elongate and has a length smaller than λ

/8.

88. The method of claim 77, in which

the excitation frequency defines a wavelength λ

, and

the first loop section has a length larger than λ

.

89. The method of claim 77, in which

the loop portions of the first, the second, and the third conductors are substantially elongate and have substantially similar lengths.

90. The method of claim 77, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that are shaped with square-like corners.

91. The method of claim 77, in which

the loop portion of the third conductor is substantially elongate and terminates in two ends that have slanted shapes.