Ground proximity antenna system
The invention provides an antenna system for operation near a ground plane, for example, at or near the surface of a body of water. The antenna system includes, for example, an array of filar elements attached to one or more spiral elements. The system also includes, for example, a buoyant support and/or housing for transporting the antenna to and/or maintaining the antenna at or near the surface of a body of water.
1. An antenna system for operation near a ground plane, the system comprising:
an antenna array, the array comprising:
a plurality of filar elements; and
a spiral element, wherein at least a first length of each of the filar elements extends radially toward a first point on a central vertical axis and wherein the spiral element is connected to at least one of the filar elements; and
a buoyant support for the antenna array.
2. The antenna system of claim 1 , wherein the plurality of filar elements comprises four filar elements and wherein the spiral element is a quadrifilar spiral element centered about the first point on the central vertical axis and connected to the four filar elements.
3. The antenna system of claim 2 , wherein the spiral element is open-ended.
4. The antenna system of claim 3 , wherein the spiral element forms a gap of about 0.2 inch at its center and wherein the spiral element is between about 2 inches and about 3 inches in diameter.
5. The antenna system of claim 2 , wherein the spiral element forms a fractional turn.
6. The antenna system of claim 5 , wherein the spiral element forms an approximately ¾ turn.
7. The antenna system of claim 2 , wherein the spiral element is about 2.5 inches in diameter.
8. The antenna system of claim 1 , wherein the antenna array comprises a top and a bottom in relation to a ground plane, and wherein the spiral element is at the top.
9. The antenna system of claim 8 , wherein the array is an end-fed array.
10. The antenna system of claim 1 , wherein the array comprises a top and a bottom in relation to a ground plane, and wherein the array comprises a first spiral element at the top and a second spiral element at the bottom.
11. The antenna system of claim 10 , wherein the array is an end-fed array.
12. The antenna system of claim 10 , wherein the array is a center-fed array.
13. The antenna system of claim 1 , wherein the support is adapted to inflate upon being deployed from a subsurface position, such that the antenna array is transportable in use to or near a surface of a body of water.
14. The antenna system of claim 1 , wherein the array comprises a top and a bottom in relation to a ground plane and wherein the support is adapted to maintain the bottom of the array at a position slightly above the ground plane.
15. The antenna system of claim 14 , wherein the position is between about 0.2 inch and about 6 inches above the ground plane.
16. The antenna system of claim 14 , wherein the position is between about 2 inches and about 4 inches above the ground plane.
17. The antenna system of claim 1 , wherein the support at least partially fills a cylindrical region defined by the array.
18. The antenna system of claim 1 , wherein the antenna array is flexible, allowing compact storage prior to being deployed.
19. The antenna system of claim 1 , wherein the system is adapted to operate at least over a 250 MHz to 270 MHz receive band and a 290 MHz to 310 MHz transmit band.
20. The antenna system of claim 1 , wherein the first length of each of the filar elements is curved.
21. The antenna system of claim 1 , wherein at least a portion of the antenna array forms a hemispheric shape.
22. The antenna system of claim 1 , wherein the spiral element is connected to each of the filar elements.
23. An antenna comprising:
a plurality of generally C-shaped filar elements orbitally disposed about a central vertical axis; and
a first spiral element centered substantially at a first point on the central vertical axis, wherein the first spiral element is open-ended and is connected to at least one of the filar elements.
24. The antenna of claim 23 , further comprising a second spiral element centered substantially at a second point on the central vertical axis, wherein the second spiral element is connected to at least one of the filar elements.
25. The antenna of claim 23 , wherein the plurality of filar elements comprises four filar elements and wherein the spiral element is quadrifilar.
26. The antenna of claim 23 , wherein the first spiral element forms a gap of about 0.2 inch at its center and wherein the spiral element is between about 2 inches and about 3 inches in diameter.
27. The antenna of claim 23 , wherein the first spiral element forms an approximately 3/4 turn.
28. The antenna of claim 23 , wherein the first spiral element is approximately 2.5 inches in diameter.
29. The antenna of claim 23 , wherein the plurality of filar elements define a substantially cylindrical volume.
30. The antenna of claim 23 , wherein the plurality of filar elements define a substantially polyhedral volume.
31. The antenna of claim 23 , wherein the plurality of filar elements comprises at least one curved C-shaped filar element.
32. The antenna of claim 23 , wherein the plurality of filar elements comprises at least one block C-shaped filar element.
33. The antenna of claim 23 , wherein the antenna array forms a hemispheric shape.
34. The antenna of claim 23 , wherein the first spiral element is connected to each of the filar elements.
35. An antenna system deployable from a subsurface position for operation near the surface of a body of water, the system comprising:
a flexible antenna array; and
an inflatable housing containing the antenna array, the housing adapted to inflate upon deployment from a subsurface position, wherein the antenna array comprises a top and a bottom in relation to a ground plane and wherein the inflatable housing is adapted to maintain the bottom of the array at a position slightly above the ground plane.
36. The antenna system of claim 35 , wherein the flexible antenna array comprises:
a plurality of filar elements; and
a spiral element connected to at least one of the filar elements.
37. The antenna system of claim 35 , wherein the position is between about 0.2 inch and about 6 inches above the ground plane.
38. An antenna comprising:
a plurality of generally C-shaped filar elements orbitally disposed about a central vertical axis; and
a first spiral element centered substantially at a first point on the central vertical axis, wherein the first spiral element forms a fractional turn and is connected to at least one of the filar elements.