Efficient electrically small loop antenna with a planar base element

• US 5,767,813 A
• Filed: 04/11/1995
• Issued: 06/16/1998
• Est. Priority Date: 05/27/1993
• Status: Expired due to Term

• Current Assignee: Savi Technology Incorporated
• Original Assignee: Raytheon TI Systems, Inc. (Rtx Corporation)
• Inventors: Verma, Vikram, Yao, Nian Jing, Balzano, Quirino
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Ho, Tan
• Application Number:
  US08/419,894
• Time in Patent Office: 1,162 Days
• Field of Search: 343/702, 343/718, 343/741, 343/742, 343/743, 343/744, 343/745, 343/748, 343/866, 343/867
• US Class Current: 343/744
• CPC Class Codes: H01Q 1/242 specially adapted for hand-held use
• 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
• CPC Class Codes: H01Q 7/005 with variable reactance for tuning the antenna
• CPC Class Codes: H01Q 9/42 with folded element, the folded parts being spaced apart a small fraction of the operating wavelength

Abstract

An efficient electrically small loop antenna includes a radiation device, an impedance matching network, and a connector that interfaces to associated electronic circuitry. The radiation device includes a conductive planar base element extending in a base plane and a conductive loop connected to the planar base element. The loop connects to the base element so that the electrical current for the antenna flows through both the conductive loop and the planar base element. The impedance matching network matches the radiation device to the associated electronic circuitry. The matching network is integrated into the planar base and is connected to both the conductive loop and the base element so that the electric current supplied to the antenna is conducted through both the base element and the conductive loop.

Claims

1. An electrically small loop antenna for connection to an electrical circuit for operation at a radiation frequency, said antenna comprising,

a radiation device conducting a resonant current for radiation at the radiation frequency, said radiation device including,

a base member having a conductive planar base element extending in a base plane for conducting said resonant current for radiation at the radiation frequency,

a conductive loop extending from a first end to a second end for conducting said resonant current for radiation at the radiation frequency, said first end connected to said conductive planar base element at a first location;

a first non-conductive window disposed in said base member at a second location extending between said conductive planar base element and said conductive loop second end;

a matching network for matching the impedance of the radiation device to the impedance of the electrical circuit, said matching network extending within said first window and connecting the second end of the conductive loop to said conductive planar base element at a third location to form a resonant circuit loop having a high Q, said resonant circuit loop including said conductive planar base element and said conductive loop whereby said resonant current is conducted through the base element and through the conductive loop; and

connector means having first and second conductors for connecting to the electrical circuit, one of said conductors connected directly to said base element and the other of said conductors connected to the matching network whereby electrical current is conducted between the electrical circuit and the radiation device.

2. The antenna of claim 1 wherein said planar base element is formed as a conductive sheet.

3. The antenna of claim 1 wherein said planar base element is formed as a conductive metal cladding on a dielectric material.

4. The antenna of claim 1 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane.

5. The antenna of claim 1 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane and wherein a portion of the resonant current in said base element is distributed outside said loop plane.

6. The antenna of claim 1 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane, wherein a portion of the resonant current in said base element is distributed outside said loop plane, and wherein a substantially greater portion of the resonant current in said base element is located on one side of said loop plane whereby the antenna radiation pattern tends to be omni-directional.

7. The antenna of claim 1 wherein said matching network includes a capacitor extending across said first window and connected between said base element and the loop element for conducting said current resonant.

8. The antenna of claim 1 wherein said base member further includes a second non-conductive window, wherein said matching network includes a first capacitor extending within said first window and connected between said conductive planar base element and the second end of the loop element, wherein a second capacitor extends within said second window and is connected between said conductive planar base element and the first end of the loop element whereby the first and second capacitors are connected in series resonance with the conductive planar base element and the loop element for conducting said radiation current.

9. The antenna of claim 8 wherein a third capacitor extends within said second window and is connected between said first end of the loop element and the conductive planar base element, said third capacitor being oriented orthogonal to said second capacitor.

10. The antenna of claim 1 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane, wherein said matching network is formed with a plurality of capacitors extending across said first window and connected between said base element and said loop element at a plurality of different capacitor locations distributed in the base plane whereby the resonant current in said base element tends to be distributed in said base plane.

11. The antenna of claim 10 wherein said capacitors extending across said first window are positioned in close proximity to said loop plane whereby the length of the conduction path for the resonant current in the radiation device and through the capacitors is minimized.

12. The antenna of claim 10 wherein said capacitors are constructed with high-loss material.

13. The antenna of claim 10 wherein said capacitors are constructed with low-loss material.

14. The antenna of claim 1 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane.

15. The antenna of claim 14 wherein said first, second and third loop elements are circular in cross-section and have a surface area small compared to the surface area of said base element in the base plane.

16. The antenna of claim 1 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where each of said first, second, third, and base elements each have lengths that are less than one tenth the wavelength of the radiation frequency.

17. The antenna of claim 1 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where said first and second loop elements have a height above said base plane that tends to optimize the antenna performance.

18. The antenna of claim 1 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane, said base element having a base element length extending in the loop plane and having a base element width extending normal to the base element length, and where said first and second loop elements have a loop element height above said base plane less than two times the base element width so as to optimize the antenna performance.

19. The antenna of claim 18 wherein said loop element height is approximately one-half the base element width.

20. The antenna of claim 1 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where said first, second and third loop elements are formed of conductors circular in cross-section having surface areas small relative to the surface area of the base element in the base plane.

21. The antenna of claim 1 wherein said matching network is formed in said first window, said matching network including,

a strip connector lying between a portion of said base element and the second end of the conductive loop,

series resonant capacitance means connecting said strip connector to said second end,

parallel matching capacitance means connecting said strip connector to said base element.

22. The antenna of claim 21 wherein said series resonant capacitance means includes first and second capacitors connected in parallel.

23. The antenna of claim 21 wherein said series resonant capacitance means include a tunable capacitor and a fixed capacitor in parallel with said tunable capacitor.

24. The antenna of claim 23 wherein said tunable capacitor has a capacitance C and has a rotating tuning element for adjusting the capacitance C where ψ

is the angle of rotation of the rotating tuning element and dC/dψ

is the rate of change of the capacitance, C, of the tunable capacitor as a function of ψ

, said tunable capacitor and said fixed capacitor having values to establish the tuning characteristics of the matched network such that a large change in ψ

due to a large rotation of the tuning element results in a small change of C.

25. The antenna of claim 21 wherein said parallel matching capacitance means includes a plurality of capacitors connected in parallel.

26. The antenna of claim 1 wherein said radiation device is for transmitting at said radiation frequency and said antenna functions to emit electromagnetic waves.

27. The antenna of claim 1 wherein said radiation device is for receiving at said radiation frequency and said antenna functions to intercept electromagnetic waves.

28. The antenna of claim 1 wherein said radiation device is for transmitting and receiving at said radiation frequency and said antenna functions to both emit and intercept electromagnetic waves.

29. An electrically small loop antenna for operation at a radiation frequency, said antenna comprising,

a radiation device conducting a resonant current for radiation at the radiation frequency, said radiation device including,

a base member having a conductive planar base element extending in a base plane for conducting said resonant current for radiation at the radiation frequency, said base member having a non-conductive window for controlling the direction of the resonant current in the planar base element,

a conductive loop extending from a first end to a second end for conducting said resonant current for radiation at the radiation frequency, said first end of the conductive loop connected to said base element at a first location and said second end of the conductive loop connected to said base member at a second location spaced from said first location, said conductive loop lying in a loop plane substantially perpendicular to said base plane, and wherein said window is configured between said conductive loop second end and said conductive planar base element for controlling the direction of the resonant current in said base element away from said loop plane to control the antenna directionality;

and

a matching network for matching the impedance of the radiation device to the impedance of the electrical circuit, said matching network extending within said window and connecting the second end of the conductive loop to the conductive planar base element at the second location to form a resonant circuit loop, said resonant circuit loop including said conductive planar base element, said conductive loop and said matching network, whereby said resonant current is conducted through the base element, the conductive loop and the matching network.

30. The antenna of claim 29 wherein said matching network includes an inductor extending across said window and connected between said base element and the loop element for conducting said resonant current.

31. The antenna of claim 30, wherein the inductor functions as a tapped transformer.

32. The antenna of claim 31 wherein said transformer includes a strip conductor and a sliding tap for making a tap connection to said strip conductor whereby the impedance transformation ratio of the transformer is changeable for tuning the antenna.

33. A communication transceiver comprising,

an electrical circuit mounted on a circuit board for operation at a radiation frequency, an electrically small loop antenna including,

a radiation device including,

a base member having a conductive planar base element extending in a base plane,

a conductive loop extending from a first end to a second end, said first end of the conductive loop connected to said conductive planar base element at a first location,

a first non conductive window disposed in said base member at a second location and extending between said conductive planar base element and said conductive loop second end,

a matching network for matching the impedance of the radiation device to the impedance of the electrical circuit, said matching network extending within said first non conductive window and connecting the second end of the conductive loop to said conductive planar base element at a third location whereby a radiation current is conducted through the base element and the conductive loop,

connector means having first and second conductors for connecting to the electrical circuit, one of said conductors connected to said base element and the other of said conductors connected to the matching network whereby a connector current is conducted between the antenna and the electrical circuit,

battery means for powering the electrical circuit,

a housing including,

means for engaging and locating the circuit board having the electrical circuit at a first level,

means for engaging and locating the base element of the radiation device at a second level parallel to and offset from the first level whereby the base element is positioned in a plane offset from the electrical circuit to isolate the electrical circuit from the conductive loop of the radiation device.

34. Communication device embodying the antenna of claim 33 wherein said base member is formed as a conductive sheet on a high-loss dielectric material.

35. The antenna of claim 33 wherein said base member is formed as a conductive sheet on a low-loss dielectric material.

36. The antenna of claim 33 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane.

37. The antenna of claim 33 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane and wherein a portion of the radiation current in said base element is distributed outside said loop plane.

38. The antenna of claim 33 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane, wherein a portion of the resonant current in said base element is distributed outside said loop plane, and wherein a substantially greater portion of the radiation current in said base element is located on one side of said loop plane whereby the antenna radiation pattern tends to be omni-directional.

39. The antenna of claim 33 wherein said matching network includes a capacitor extending within said first window connected to said base element.

40. The antenna of claim 33 wherein said base member further includes a second nonconductive window, wherein said matching network includes a first capacitor extending within said first window and is connected between said conductive planar base element and said second end of the loop element, wherein a second capacitor is connected between said conductive planar base element and the first end of the loop element whereby the first and second capacitors are connected in series.

41. The antenna of claim 40 wherein a third capacitor extends within said second window and is connected between said first end of the loop element and the conductive planar base element, said third capacitor being oriented orthogonal to said second capacitor.

42. The antenna of claim 33 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane and wherein said antenna includes means for controlling the direction of the radiation current in said base element to control the antenna directionality.

43. The antenna of claim 33 wherein said base plane includes a non-conductive window and wherein said matching network includes an inductor in said window connected to said base element.

44. The antenna of claim 43 wherein the inductor is a tapped transformer.

45. The antenna of claim 44 wherein said transformer includes a strip conductor and a sliding tap for making a tap connection to said strip conductor whereby the impedance transformation ratio of the transformer is changeable for tuning the antenna.

46. The antenna of claim 33 wherein said conductive loop lies in a loop plane substantially perpendicular to said base plane, wherein said matching network is formed with a plurality of capacitors located in said window and connected to said base element at a plurality of different capacitor locations distributed in the base plane whereby the radiation current in said base element tends to be distributed in said base plane.

47. The antenna of claim 46 wherein said capacitors located in said window are positioned in close proximity to said loop plane whereby the length of the conduction path for the radiation current in the radiation device is minimized.

48. The antenna of claim 46 wherein said capacitors are constructed with high-loss material.

49. The antenna of claim 46 wherein said capacitors are constructed with low-loss material.

50. The antenna of claim 33 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane.

51. The antenna of claim 50 wherein said first, second and third loop elements are circular in cross-section, having a surface area small compared to the surface area of said base element in the base plane.

52. The antenna of claim 33 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where each of said first, second, third, and base elements have lengths that are less than one tenth the wavelength of the radiation frequency.

53. The antenna of claim 33 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where said first and second loop elements have a height above said base plane that tends to optimize the antenna performance.

54. The antenna of claim 33 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane, said base element having a base element length extending in the loop plane and having a base element width extending normal to the base element length, and where said first and second loop elements have a loop element height above said base plane less than two times the base element width so as to optimize the antenna performance.

55. The antenna of claim 54 wherein said loop element height is approximately one-half the base element width.

56. The antenna of claim 33 wherein said conductive loop includes first and second loop elements substantially perpendicular to said base plane and a third loop element substantially parallel to said base plane and where said first, second and third loop elements are circular in cross-section having surface areas small relative to the surface area of the base element in the base plane.

57. The antenna of claim 33, said matching network including,

a strip connector lying between a portion of said base element and the second end of the conductive loop,

series resonant capacitance means connecting said strip connector to said second end,

parallel matching capacitance means connecting said strip connector to said base element.

58. The antenna of claim 57 wherein said series resonant capacitance means includes first and second capacitors connected in parallel.

59. The antenna of claim 57 wherein said series resonant capacitors include a tunable capacitor and a fixed capacitor in parallel with said tunable capacitor.

60. The antenna of claim 59 wherein said tunable capacitor has a capacitance C and has a rotating tuning element for adjusting the capacitance C where ψ

is the angle of rotation of the rotating tuning element and dC/dψ

is the rate of change of the capacitance, C, of the tunable capacitor as a function of ψ

, said tunable capacitor and said fixed capacitor having values to establish the tuning characteristics of the matched network such that large changes in ψ

from large rotations of the tuning element result in small changes of C.

61. The antenna of claim 57 wherein said parallel matching capacitance means includes a plurality of capacitors connected in parallel.

62. The antenna of claim 33 wherein said radiation device is for transmitting at said radiation frequency.

63. The antenna of claim 33 wherein said radiation device is for receiving at said radiation frequency.

64. The antenna of claim 33 wherein said radiation device is for transmitting and receiving at said radiation frequency.

65. An electrically small loop antenna for connection to an electrical circuit for operation at a radiation frequency comprising,

a radiator including,

a conductive loop having a height and extending in a loop plane from a first end to a second end,

a base member having a conductive planar base element free of electrical components extending in a base plane substantially perpendicular to said loop plane, said conductive planar base element forming a non-conductive window, said window extending in a direction perpendicular to said loop plane,

said first end of the conductive loop connected to said conductive planar base element at a location removed from said window, and said second end of the conductive loop connected to said base member at a location within and encompassed by said window;

connector means having first and second conductors for connecting the antenna to the electrical circuit, one of said conductors connected to said base element; and

a matching network extending within said window and connecting the second end of the conductive loop to the conductive planar base element and to the other one of said conductors whereby radiation current is conducted through the base element and the conductive loop and whereby the antenna is matched to the electrical circuit.

66. The antenna of claim 65 wherein said matching network is formed across said window, said matching network including,

a strip connector lying between a portion of said base element and the second end of the conductive loop,

series resonant capacitors connected in parallel connecting said strip connector to said second end,

parallel matching capacitors connected in parallel connecting said strip connector to said base element.

67. An electrically small loop antenna for connection to an electrical circuit for operation at a radiation frequency, said antenna comprising,

a radiation device conducting a resonant current for radiation at the radiation frequency, said radiation device including,

a base member having a conductive planar base element extending in a base plane for conducting said resonant current for radiation at the radiation frequency, said base member having a non conductive window,

a conductive loop extending from a first end to a second end for conducting said resonant current for radiation at the radiation frequency,

said first end connected to said conductive planar base element at a first location and said second end connected to said base member at a second location spaced from said first location to enable said resonant current to conduct through the conductive planar base element and the conductive loop;

a matching network extending within said window for matching the impedance of the radiation device to the impedance of the electrical circuit, said matching network connecting the second end of the conductive loop to the conductive planar base element at the second location to form a resonant circuit loop having a Q greater than 10, said resonant circuit loop including said conductive planar base element and said conductive loop whereby said resonant current is conducted through the base element and through the conductive loop; and

connector means having first and second conductors for connecting to the electrical circuit, one of said conductors connected directly to said base element and the other of said conductors connected to the matching network whereby electrical current is conducted between the electrical circuit and the radiation device.

68. An electrically small loop antenna for operation at a radiation frequency, said antenna comprising,

a radiation device conducting a resonant current for radiation at the radiation frequency, said radiation device including,

a base member having a conductive planar base element extending in a base plane for conducting said resonant current for radiation at the radiation frequency, said base member having a first and a second non-conductive window for controlling the direction of the resonant current in the base element,

a conductive loop having a height and extending from a first end to a second end for conducting said resonant current for radiation at the radiation frequency, said first end of the conductive loop connected to said base member at a first location and said second end of the conductive loop connected to said base member at a second location spaced from said first location, said conductive loop lying in a loop plane substantially perpendicular to said base plane, and

wherein said second window is configured about said conductive loop second end and said first window is configured about said conductive loop first end to extend a substantial amount of the resonant current away from said loop plane, wherein a capacitor extends within said first window between said loop element first end and said conductive planar base element, said first and second windows controlling the direction of the resonant current in said base element away from said loop plane and thereby determine the antenna directionality;

and

a matching network for matching the impedance of the radiation device to the impedance of the electrical circuit, said matching network extending across said second non conductive window and connecting the second end of the conductive loop to the conductive planar base element at the second location to form a resonant circuit loop, said resonant circuit loop including said conductive planar base element, said conductive loop, said capacitor and said matching network.