Dual-frequency choke-ring ground planes

• US 6,278,407 B1
• Filed: 02/23/1999
• Issued: 08/21/2001
• Est. Priority Date: 02/24/1998
• Status: Expired due to Term

• Current Assignee: Topcon GPS, LLC
• Original Assignee: Topcon Positioning Systems Incorporated (Topcon Corporation)
• Inventors: Sutjagin, Igor V., Astakhov, Andrej V., Filippov, Vladimir S., Ashjaee, Javad, Tatarnikov, Dmitry V.
• Primary Examiner(s): Ho, Tan
• Application Number:
  US09/255,932
• Time in Patent Office: 910 Days
• Field of Search: 343/700.MS, 343/846, 343/848, 343/785, 343/786, 343/756, 343/909
• US Class Current: 343/700.0MS
• CPC Class Codes: H01Q 19/10 using reflecting surfaces
• 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 9/0478 with means for suppressing spurious modes, e.g. cross polarisation

Abstract

Choke-ring ground planes are commonly used for multipath rejection in geodetic surveying systems. Such ground planes consist of a thick metal disc with deep grooves on one of the flat surfaces. An antenna is mounted in the center of the grooved surface. Known ground planes used in dual frequency communication systems (L1 and L2) could not be constructed to have good rejection of multipath signals in both L1 and L2 frequencies; instead, they are constructed for good rejection of multipath signals in L2 but not good for the rejection of multipath signals in L1. A first invention provides for equally good multipath rejection for both L1 and L2 frequencies by incorporating novel electromagnetic filter structures within the choke-ring grooves. The filter structures of the present invention enable the choke ring to provide multipath rejection in each frequency band which is as good as, or better than, the multipath rejection achieved in the L2 band with existing devices. A second invention provides for groove depths which are less than one-quarter wavelength of the frequency which has the longer wavelength (e.g., the L2 frequency in the GPS system). The shorter groove depth of the second invention provides better multipath rejection for the L2. Both inventions may be used together to improve multipath rejection for both L1 and L2 bands. A third invention of the application relates to methods of constructing choke ring ground planes which may be applied to the other inventions disclosed herein as well as existing prior art ground planes and future ground planes.

Claims

1. A choke ring ground plane for an antenna, said ground plane comprising:

a circular-shaped body having a top surface, a bottom surface, a thickness between said top and bottom surfaces, said top surface having periphery and a center point at the center of said top surface;

a plurality of concentric grooves formed in the top surface of said circular-shaped body, said grooves being centered about said center point;

an intermediate ground plane located in one of said grooves, said intermediate ground plane being parallel to said top surface;

at least one aperture formed in said intermediate ground plane, and

at least one electromagnetic filter disposed at each said aperture.

2. The ground plane of claim 1 wherein a plurality of electromagnetic filters are disposed at each said aperture.

3. The ground plane of claim 1 further comprising a plurality of additional intermediate ground planes, each said intermediate ground plane being located in a respective one of said grooves, and being parallel to the top surface.

4. The ground plane of claim 3 wherein each said intermediate ground plane has a plurality of apertures formed through it, said apertures being spaced from one another at equal angular intervals about said center point.

5. The ground plane of claim 4 wherein a first one of said grooves is closer to the center point than a second one of said grooves, and wherein the second one of said grooves has more apertures formed through it than the first one of said grooves.

6. The ground plane of claim 3 wherein said intermediate ground plane has a plurality of apertures formed through it, said apertures being spaced from one another at equal angular intervals about said center point.

7. The ground plane of claim 1 wherein said intermediate ground plane is spaced from said top surface by a distance in the range of approximately 38 mm to approximately 50 mm.

8. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

2, said first wavelength A being shorter than said second wavelength λ

₂, wherein said intermediate ground plane is spaced from said top surface by a distance in the range of one-fifth of λ

₁ to one-fourth of λ

₁.

9. The ground plane of claim 1 wherein said intermediate ground plane is spaced from said top surface by a distance in the range of approximately 38 mm to approximately 42 mm.

10. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said first wavelength λ

₁ being shorter than said second wavelength λ

₂, wherein said intermediate ground plane is spaced from said top surface by a distance in the range of {fraction (7/32)}·

λ

₁ to {fraction (15/76)}·

λ

₁.

11. The ground plane of claim 1 wherein said intermediate ground plane is spaced from said top surface by a distance in the range of approximately 46 mm to approximately 50 mm.

12. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said first wavelength λ

₁ being shorter than said second wavelength λ

₂, wherein said intermediate ground plane is spaced from said top surface by a distance in the range of 0.95·

λ

₁/4 to 1.05·

λ

₁/4.

13. The ground plane of claim 1 wherein said aperture comprises a slot having a length in the range of between approximately 90 mm to approximately 130 mm, and a slot width of less than 4.8 mm.

14. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said first wavelength λ

₁ being shorter than said second wavelength λ

₂;

wherein said aperture comprises a slot, wherein dielectric material is disposed next to said slot such that said slot has an effective relative dielectric constant ε

_{eff, S-L} which is different from unity, and wherein the slot has a length of between $\frac{0.74}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{1.15}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}.$

15. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said first wavelength λ

₁ being shorter than said second wavelength λ

₂, and wherein the slot has a length of between 0.74·

λ

₂/2 and 1.15·

λ

₂/2.

16. The ground plane of claim 1 wherein said electromagnetic filter comprises a first conductive stub crossing said aperture, said first conductive stub having at least one of its ends grounded to said intermediate ground plane.

17. The ground plane of claim 16 wherein said electromagnetic filter further comprises a second conductive stub crossing said aperture, said second conductive stub having at least one of its ends grounded to said intermediate ground plane.

18. The ground plane of claim 16 wherein said first conductive stub comprises an electrical trace formed on a dielectric board.

19. The ground plane of claim 16 wherein said first conductive stub comprises a wire suspended in air.

20. The ground plane of claim 16 wherein said intermediate ground plane comprises a dielectric board having an annular-ring shape, a conductive layer disposed on a first side of said dielectric board, and an aperture formed in said conductive layer,

wherein said first conductive stub comprises a conductive trace formed on the second side of said dielectric board and a conductive through-hole between said conductive trace and said conductive layer on said first side, and

wherein a portion of said conductive trace overlies the aperture formed in said conductive layer.

21. The ground plane of claim 17 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said first wavelength λ

₁ being shorter than said second wavelength λ

₂, said first conductive stub, second conductive stub, and said aperture blocking the transmission of the signals at the first frequency through said aperture to a greater degree than the signals at the second frequency.

22. The ground plane of claim 21 wherein a signal at the first frequency has an in-line wavelength of λ

′

₁ when it propagates along the length of said first stub, wherein one end of said first stub is open, and wherein the length of said first stub is within ±

0.1·

λ

₁/4 of the quantity;

λ

′

₁(2n+1)/4, where n is any integer number from 0 to infinity.

23. The ground plane of claim 22 wherein said aperture comprises a slot having a length in the range of 0.95·

λ

₂/2 and 1.05·

λ

₂/2.

24. The ground plane of claim 22 wherein said aperture comprises a slot, wherein dielectric material is disposed next to said slot such that said slot has an effective relative dielectric constant δ

_eff,S-L which is different from unity, and wherein the slot has a length of between $\frac{0.74}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{1.15}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}.$

25. The ground plane of claim 21 wherein the length of said first stub is between 0.9·

λ

′

₁/4 and 1.1·

λ

′

₁/4.

26. The ground plane of claim 21 wherein a signal at said first frequency has an in-line wavelength of λ

′

₁ when it propagates along the length of said first stub, wherein said first conductive stub has both of its ends grounded to said intermediate ground plane, and wherein the length of said first stub is within ±

0.1·

λ

′

₁/2 of the quantity;

λ

′

₁·

n/2, where n is any integer number from 1 to infinity.

27. The ground plane of claim 26 wherein the length of said first stub is between 0.9·

λ

′

₁/2 and 1.1·

λ

′

₁/2.

28. The ground plane of claim 26 wherein said aperture comprises a slot having a length in the range of 0.95·

λ

₂/2 and 1.05·

λ

₂/2.

29. The ground plane of claim 26 wherein said aperture comprises a slot, wherein dielectric material is disposed next to said slot such that said slot has an effective relative dielectric constant ε

_{eff, S-L} which is different from unity, and wherein the slot has a length of between $\frac{0.74}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{1.15}{\sqrt{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff},S-L}}}·<br><br>\frac{{\mathrm{\lambda <br><br>}}_2}{2}.$

30. The ground plane of claim 21 wherein the depth of each groove is between approximately 0.88·

λ

₂/4 and approximately 0.98·

λ

₂/4.

31. The ground plane of claim 21 wherein the depth of each groove is between approximately 0.92·

λ

₂/4 and approximately 0.97·

λ

₂/4.

32. The ground plane of claim 1 wherein said ground plane is for receiving signals at a first frequency having a first wavelength λ

₁ and signals at a second frequency having a second wavelength λ

₂, said second wavelength λ

₂ being greater than said first wavelength λ

₁.

wherein the groove in which the intermediate ground plane is located has an inner side wall and an outer side wall, wherein the radial distance from said center point to the inner side wall is r_min and the distance from said center point to the outer side wall is r_max, and wherein said choke ring ground plane comprises at least 2λ

(r_min+r_max)/λ

₂+1 apertures in said intermediate ground plane.

33. The ground plane of claim 1 wherein said aperture comprises a slot have a first end portion, a central portion, and a second end portion, wherein said central portion has an arc shape and is disposed on a radius of said center point, and wherein said end portions are bent with respect to said central portion.

34. The ground plane of claim 33 wherein said end portions are bent inward toward said center point and contact a groove wall.

35. The ground plane of claim 33 wherein said end portions are bent outward away from said center point and contact a groove wall.

36. The ground plane of claim I wherein said ground plane comprises three concentric grooves and three intermediate ground planes, each intermediate ground plane being disposed in a corresponding one of said grooves and being parallel to said top surface, said three concentric grooves being adjacent to one another so that there is an innermost groove, a middle groove, and an outermost groove, said ground plane further comprising six apertures formed in the intermediate ground plane which is disposed in the innermost groove, eight apertures formed in the intermediate ground plane which is disposed in the middle groove, and ten apertures formed in the intermediate ground plane which is disposed in the outermost groove.

37. A choke ring ground plane for an antenna, said antenna for receiving a broadcast signal having a wavelength λ

, said choke ring ground plane comprising;

a circular-shaped body having a top surface, a bottom surface, a thickness between said top and bottom surfaces, said top surface having periphery and a center point at the center of said top surface and a central portion disposed at said center point for receiving the antenna; and

a plurality of concentric grooves formed in the top surface of said circular-shaped body, wherein said grooves are centered about said center point and encircling the central portion for receiving the antenna, and wherein each groove has a depth which is between approximately 0.88·

λ

/4 and approximately 0.98·

λ

/4 of the broadcast signal such that the signal magnitude at the antenna for multipath versions of the broadcast signal are reduced in value.

38. The ground plane of claim 37 wherein the depth of each groove is between approximately 0.92·

λ

/4 and approximately 0.97·

λ

/4.

39. The ground plane of claim 37 wherein the broadcast signal comprises a global positioning signal with a wavelength of 24.4 cm.

40. The ground plane of claim 39 wherein the depth of each groove is between approximately 54 mm and approximately 60 mm.

41. The ground plane of claim 40 wherein the width of each groove is between approximately 20 mm and 24 mm.

42. The ground plane of claim 40 wherein the width of each groove is between approximately 21 mm and 23 mm.

43. The ground plane of claim 37 wherein the broadcast signal comprises a global positioning signal with a wavelength of 19 cm, and wherein the depth of each groove is between approximately 41.5 mm and approximately 46.5 mm.

44. The ground plane of claim 43 wherein the width of each groove is between approximately 20 mm and 24 mm.

45. The ground plane of claim 37 comprising at least three said grooves.

46. The ground plane of claim 37 wherein one of said grooves has an inner diameter which is smaller than the inner diameters of the other grooves and which has a value of approximately 190 mm.

47. The ground plane of claim 46 wherein the central portion for receiving the antenna is recessed from said top surface of the body by an amount which is in the range from approximately 20 mm to approximately 27 mm.

48. The ground plane of claim 37 wherein the plurality of grooves are referenced by an identifying index designated herein as index “

K”

, wherein each K-th groove has an inner side wall and an outer side wall, wherein the radial distance from said center point to the inner side wall is R_I,K and the distance from said center point to the outer side wall is R_O,K wherein the K-th groove has a corresponding radial width W_K=R_O,K−

R_I,K and an average circumferential length L_K=2π

(R_O,K+R_I,K)/2;

wherein the width WK of each groove is less than the wavelength λ

of the broadcast signal, and wherein the length L_K of each groove is greater than the wavelength λ

of the broadcast signal.

49. A method of manufacturing a choke-ring ground plane comprising the steps of:

(a) forming a dielectric body in the shape of the choke-ring ground plane having a plurality of grooves, and

(b) forming a thin layer of conductive material over the surfaces of said dielectric body.

50. The method of claim 49 wherein said dielectric body comprises a polymeric material, and wherein said step (a) comprising the step of injecting said polymeric material into a mold under pressure.

51. The method of claim 50 wherein said dielectric comprises a thermosetting polymeric material.

52. The method of claim 49 wherein said step (b) comprises the step of electroless plating a metal onto said dielectric body.

53. The method of claim 49 wherein said step (b) comprises the step of painting a conductive material onto said dielectric body.

54. The method of claim 49 wherein said step (b) comprises the step of dip-coating said dielectric body in a bath of conductive paint.

55. A choke ring ground plane comprising:

a dielectric body having a circular top surface having a diameter of at least 200 mm, a circular bottom surface, a thickness between the top and bottom surfaces, a plurality of grooves formed in said top surface of said dielectric body; and

a layer of conductive material formed over the surfaces of the grooved dielectric body.

56. The choke ring ground plane of claim 55 wherein said dielectric body comprises a polymeric material.

57. The choke ring ground plane of claim 55 wherein said polymeric material comprises a plastic.

58. The choke ring ground plane of claim 55 wherein the thickness is of at least 38 mm in value.

59. The choke ring ground plane of claim 55 wherein the thickness is of at least 42 mm in value.

60. The choke ring ground plane of claim 55 wherein said dielectric body further comprises a recessed central portion disposed on the body'"'"'s top surface for receiving an antenna.

61. The choke ring ground plane of claim 55 wherein the grooves have respective depths, and where the groove depths are equal.

62. A choke ring ground plane for an antenna, said antenna for receiving a broadcast signal having a wavelength λ

, said choke ring ground plane comprising;

a circular-shaped body having a top surface, a bottom surface, a thickness between said top and bottom surfaces, said top surface having periphery and a center point at the center of said top surface; and

a plurality of concentric grooves formed in the top surface of said circular-shaped body, wherein each groove has a depth which is between approximately 0.88·

λ

/4 and approximately 0.98·

λ

/4 of the wavelength λ

of the broadcast signal.

63. The ground plane of claim 62 wherein the depth of each groove is between approximately 0.92·

λ

/4 and approximately 0.97·

λ

/4.

64. The ground plane of claim 62 wherein the width of each groove is between approximately 20 mm and 24 mm.

65. The ground plane of claim 62 wherein one of said grooves has an inner diameter which is smaller than the inner diameters of the other grooves and which has a value of approximately 190 mm.