Quadrifilar helical antenna

• US 20060022891A1
• Filed: 11/26/2004
• Published: 02/02/2006
• Est. Priority Date: 07/28/2004
• Status: Active Grant

• Current Assignee: SkyCross, Inc.
• Original Assignee: SkyCross, Inc.
• Inventors: Choi, Sang Ok, Oh, Se-hyun, Farrar, John C., Han, Eun Seok, O'Neill, Gregory A. Jr., Lee, Myung Sung, Yoon, Jin Hee, Jo, Young-Min, Fugate, Murray, Lee, Joo Mun
• Granted Patent: US 7,245,268 B2
• Time in Patent Office: Days
• US Class Current: 343/895
• CPC Class Codes: H01Q 11/08 Helical antennas

Abstract

A quadrifilar helical antenna comprising two pairs of filars having unequal lengths and phase quadrature signals propagating thereon. A conductive H-shaped impedance matching element matches a source impedance to an antenna impedance. The impedance matching element having a feed terminal at the center thereof from which current is supplied to the two filars of each filar pair disposed about an edge of the impedance matching element and symmetric with respect to a center of the impedance matching element. The impedance matching element further comprises a reactive element for matching the antenna and source impedances.

Claims

1. A quadrifilar helical antenna, comprising:

a first pair of serially connected helical filars having a first length and a first and a second end;

a second pair of serially connected helical filars having a second length different from the first length and having a third and a fourth end; and

an impedance matching element conductively connected to the first, second, third and fourth ends for matching an antenna load impedance to a source impedance.

2. The quadrifilar helical antenna of claim 1 wherein the antenna load impedance comprises a resistive component and a series positive reactive component.

3. The quadrifilar helical antenna of claim 2 wherein the reactive component comprises a reactive component having a magnitude of about twice a magnitude of the resistive component.

4. The quadrifilar helical antenna of claim 1 wherein the source impedance is 50 ohms and a series resistance component of the antenna impedance is less than the source impedance.

5. The quadrifilar helical antenna of claim 1 wherein the first filar length is longer than a resonant length at a resonant frequency and the second filar length is shorter than the resonant length at the resonant frequency.

6. The quadrifilar helical antenna of claim 1 wherein the antenna load impedance comprises a resistive component and an inductive component, and wherein a magnitude of the resistive component and the inductive component is responsive to a diameter of a cylinder on which the first and the second pairs of filars are disposed, and wherein the antenna load impedance declines as the diameter is reduced.

7. The quadrifilar helical antenna of claim 6 wherein the diameter is selected to provide an antenna load impedance that can be transformed to 50 ohms by the impedance matching element.

8. The quadrifilar helical antenna of claim 6 wherein a range of diameters comprises diameters above about 5 mm.

9. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a capacitor selected from a lumped capacitor and a distributed capacitor.

10. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises an inductor selected from a lumped inductor and a distributed inductor.

11. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a capacitor selected from a lumped capacitor and a distributed capacitor and an inductor selected from a lumped inductor and a distributed inductor.

12. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a substrate, and wherein the first pair of filars and the second pair of filars are disposed symmetrically with respect to a center of the substrate.

13. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a planar substrate having four slots disposed proximate an edge thereof and symmetrical with respect to a center of the substrate, and wherein the first, second, third and fourth ends are each disposed in a one of the four slots.

14. The quadrifilar helical antenna of claim 1 wherein the first pair of filars comprises a first and a second filar connected by a first conductive bridge and the second pair of filars comprises a third and a fourth filar connected by a second conductive bridge, and wherein the first and the second conductive bridges are insulated from each other, and wherein the first, second, third and fourth ends are connected to the impedance matching element,

15. The quadrifilar helical antenna of claim 14 wherein the first conductive bridge and the second conductive bridge are disposed on opposing surfaces of a dielectric substrate.

16. The quadrifilar helical antenna of claim 15 wherein the first and the second pairs of filars are disposed on a flexible substrate in the shape of a cylinder, and wherein the dielectric substrate is disposed at a first end of the cylinder.

17. The quadrifilar helical antenna of claim 1 wherein the antenna load impedance comprises a resistive component less than 50 ohms and a reactive component.

18. The quadrifilar helical antenna of claim 1 wherein a signal conductor supplies a signal to the quadrifilar helical antenna, and wherein the impedance matching element comprises a capacitor in series with the signal conductor and an inductor in parallel with the signal source.

19. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a conductive pattern and reactive components connected thereto, and wherein the conductive pattern contributes an inductive component to the antenna load impedance.

20. The quadrifilar helical antenna of claim 1 wherein the impedance matching element comprises a substantially circular dielectric substrate having conductive traces and one or more reactive components disposed thereon, and wherein the impedance matching element is disposed at a lower end of a cylinder about which the first and the second pair of filars are disposed.

22. The quadrifilar helical antenna of claim 1 exhibiting predetermined operating parameters in response to the first length and the second length.

23. The quadrifilar helical antenna of claim 22 wherein the one or more antenna operating parameters comprises one or more of gain over a solid angle and bandwidth.

24. The quadrifilar helical antenna of claim 1 wherein the first pair of filars comprises a first and a second conductor each having a first end disposed at an antenna base and helically disposed in a direction of an antenna top, the antenna further comprising a first conductive bridge connecting the first and the second conductors proximate the antenna top, and wherein the second pair of filars comprises a third and a fourth conductor each having a first end disposed at an antenna base and helically disposed in a direction of an antenna top, the antenna further comprising a second conductive bridge connecting the third and the fourth conductors proximate the antenna top.

25. The quadrifilar helical antenna of claim 1 wherein a pitch angle of the first, second, third and fourth conductors is about 60 degrees.

26. The quadrifilar helical antenna of claim 1 wherein a pitch angle of the first, second, third and fourth conductors is between about 60 degrees and about 75 degrees.

27. The quadrifilar helical antenna of claim 1 wherein the second length different than the first length creates a quadrature phase relationship for signals propagating on the first and the second pairs of filars to produce a circularly polarized signal when the antenna is operative in a transmit mode.

28. The quadrifilar helical antenna of claim 1 wherein the first pair of filars exhibits a first resistance and an inductive reactance and the second pair of filars exhibits a second resistance and a capacitive reactance, and wherein the first resistance is substantially equal to a magnitude of the inductive reactance, the second resistance is substantially equal to a magnitude of the capacitive reactance, and the magnitude of the inductive reactance is substantially equal to the magnitude of the capacitive reactance.

29. The quadrifilar helical antenna of claim 1 wherein a length of the first pair of filars is longer than a quarter wavelength at an antenna resonant frequency and a length of the second pair of filars is shorter than a quarter wavelength at the resonant frequency.

30. The quadrifilar helical antenna of claim 1 wherein a length of the first pair of filars is longer than a half wavelength at an antenna resonant frequency and a length of the second pair of filars is shorter than a half wavelength at the resonant frequency.

31. The quadrifilar helical antenna of claim 1 wherein a length of the first pair of filars is longer than an integer multiple of a quarter wavelength at an antenna resonant frequency and a length of the second pair of filars is shorter than an integer multiple of a quarter wavelength at the resonant frequency.

32. The quadrifilar helical antenna of claim 1 wherein the first and the second pairs of filars are helically disposed in a shape of a cylinder, and wherein the first and the second pairs of filars are equidistant from an axis of the cylinder.

33. The quadrifilar helical antenna of claim 1 wherein the first pair of filars comprises first and second filars helically disposed in a cylindrical shape, and wherein the second pair of filars comprises third and fourth filars helically disposed in a cylindrical shape, and wherein each of the first, second, third and fourth filars comprises an open end at an upper edge of the cylindrical shape, the antenna further comprising a first conductive strip electrically connecting the open end of the first and the second filars and a second conductive strip electrically connecting the open end of the third and the fourth filars, and wherein a dielectric gap between the first and the second conductive strips is related to a length differential between the first and the second pair of filars.

34. The quadrifilar helical antenna of claim 33 wherein the upper edge comprises a castellated edge.

35. The quadrifilar helical antenna of claim 33 wherein the first conductive strip is formed on a first dielectric substrate and the second conductive strip is formed on a second dielectric substrate spaced apart from the first dielectric substrate to form a dielectric gap therebetween, and wherein the length of the gap is related to the length differential.

36. The quadrifilar helical antenna of claim 1 wherein the first pair of filars comprises first and second filars, and wherein the second pair of filars comprises third and fourth filars, and wherein each of the first, second, third and fourth filars has a different length.

37. The quadrifilar helical antenna of claim 1 wherein the first pair of filars comprises first and second filars, and wherein the second pair of filars comprises third and fourth filars, and wherein each of the first and the second filars has a first length, and wherein each of the third and the fourth filars has a second length different from the first length.

38. The quadrifilar helical antenna of claim 1 wherein the first and the second pairs of filars are helically disposed on a cylindrical surface, the antenna further comprising a length of dielectric tape disposed on a surface of the cylindrical shape for altering a resonant frequency of the antenna.

39. The quadrifilar helical antenna of claim 1 wherein the first and the second pairs of filars present a first and a second impedance, respectively, and wherein the first and the second impedances are a conjugate pair.

21. The quadrifilar helical antenna of clam 1 wherein the first pair of filars and the second pair of filars are disposed in a helical pitch pattern about a cylindrical substrate and are symmetrical with respect to an axis of the quadrifilar helical antenna.

40. A communications handset comprising an enclosure and a quadrifilar helical antenna comprising a plurality of filars disposed on a cylindrical surface, wherein the antenna is mounted external to the enclosure, and wherein a complete length of the filars extend beyond the enclosure.

41. A quadrifilar helical antenna, comprising:

a first pair of filars having a first length;

a second pair of filars having a second length different from the first length; and

an H-shaped impedance matching element supplying current to a first end of each of the first and the second pairs of filars from current feed points disposed symmetrically with respect to an approximate center of the H-shaped impedance matching element, wherein the H-shaped impedance matching element further comprises a reactive element for matching an antenna impedance to a source impedance.

42. The quadrifilar helical antenna of claim 41 wherein the H-shaped impedance matching element comprises four legs, and wherein a current feed point is disposed at a free end of each leg, and wherein the reactive element comprises at least one of a capacitive element and an inductive element.

43. The quadrifilar helical antenna of claim 41 wherein the first pair of filars each comprise a second end connected by a first conductive bridge element, and wherein the second pair of filars each comprise a second end connected by a second conductive bridge.

44. The quadrifilar helical antenna of claim 41 wherein the first and the second pairs of filars are disposed on a flexible substrate having a cylindrical shape.

45. The quadrifilar helical antenna of claim 41 wherein the H-shaped impedance matching element further comprises a substrate having an H-shaped conductive pattern disposed thereon, and wherein a signal feed terminal is disposed at an approximate center of the H-shaped conductive pattern.

46. The quadrifilar helical antenna of claim 45 wherein current is supplied from the signal feed terminal to the current feed points, and wherein the reactive element comprises at least one of a capacitor in series with the signal source and an inductor in parallel with the signal source.

47. The quadrifilar helical antenna of claim 41 wherein the current supplied to each of the first and the second filar pairs is approximately equal.

48. The quadrifilar helical antenna of claim 41 wherein a current in the first pair of filars is in an approximate quadrature relationship with a current in the second pair of filars.

49. The quadrifilar helical antenna of claim 41 wherein at least one of an antenna bandwidth and an antenna gain are responsive to a difference between the first and the second lengths.

50. The quadrifilar helical antenna of claim 41 wherein the first pair of filars comprises a first and a second conductor each helically oriented between an antenna base and an antenna top, and wherein the second pair of filars comprises a third and a fourth conductor each helically oriented between the antenna base and the antenna top, and wherein the first, second, third and fourth conductors are disposed at a pitch angle.

51. The quadrifilar helical antenna of claim 50 wherein the pitch angle comprises a pitch angle of about 60 degrees.

52. A quadrifilar helical antenna for connecting to a feed conductor having a first and a second conductive element, the antenna comprising:

a first pair of filars having a first length and comprising a first and a second filar each helically oriented between an antenna base and an antenna top;

a second pair of filars having a second length different from the first length and comprising a third and a fourth filar each helically oriented between the antenna base and the antenna top;

a substrate supporting a conductive H-shaped pattern for receiving a first end of each one of the first, second, third and fourth filars at a free end of each leg of the H-shaped conductive pattern, wherein a first element of the conductive pattern connects the first and the third filars and a second element of the conductive pattern connects the second and the fourth filars;

a first reactive element for connecting between a first interior terminal of the conductive H-shaped pattern and the first conductive element;

wherein the conductive H-shaped pattern further comprises a second interior terminal for connecting to the second conductive element;

a second reactive element for connecting between the first and the second conductive elements

a first conductive bridge for connecting a second end of the first and the second filars proximate the antenna top; and

a second conductive bridge for connecting a second end of the third and the fourth filars proximate the antenna top, wherein the first and the second conductive bridges are spaced apart by a distance d, such that a length differential between the fist and the second pairs of filars is responsive to the distance d.

53. A method for designing a quadrifilar helical antenna in a shape of a cylinder, having at least one of a predetermined height and diameter, comprising:

determining a length of a first filar loop to present an impedance having a real component and an inductive component;

determining a length of a second filar loop to present an impedance having a real component substantially equal to the real component of the first filar loop and having a capacitive component, wherein a magnitude of the inductive component is substantially equal to a magnitude of the capacitive component; and

determining an impedance matching element connected to the first and the second filar loops for matching an antenna impedance to a source impedance.

54. The method of claim 53 wherein the step of determining the impedance matching element further comprises determining at least one of an inductance and a capacitance for matching the antenna impedance to the source impedance.

55. The method of claim 54 wherein the source impedance comprises a nominal 50 ohm impedance.

56. The method of claim 53 further comprising determining a pitch angle of the first and the second filar loops.

57. The method of claim 53 further comprising adjusting the length of the first filar loop and the second filar loop to achieve desired antenna gain and bandwidth operational parameters, wherein the gain and the bandwidth are inversely related.

58. The method of claim 53 wherein the step of determining the impedance matching element further comprises determining a value of at least one of an inductor and a capacitor of the impedance matching element.

60. The method of claim 53 wherein the step of determining a length of the first filar loop comprises determining the real component of the first filar loop impedance substantially equal to a magnitude of the inductive component.

61. The method of claim 53 wherein the step of determining a length of the second filar loop comprises determining the real component of the second filar loop impedance substantially equal to a magnitude of the capacitive component.