Ultra-wideband antennas

1. An antipodal antenna comprising an active element located between a pair of matched, symmetrically diverging, ground elements.

2. The antenna of claim 1 wherein inside edge portions of the active element and ground elements at distal ends of the active and ground elements diverge from one another to provide a tapered slot.

3. The antenna of claim 2 wherein the tapered slot is symmetrical with respect to a centerline.

4. The antenna of claim 3 wherein the active element comprises a broad distal portion supported at an end of a thinner member.

5. The antenna of claim 4 wherein the ground elements each comprise a broad distal portion supported at an end of a thinner member.

6. The antenna of claim 4 wherein the broad distal portion of the active element is entirely on a first side of the centerline.

7. The antenna of claim 6 wherein the broad distal portions of the ground elements are entirely on a second side of the centerline.

8. The antenna of claim 2 wherein the inside edge portions of the active element and ground elements follow convex exponential curves.

9. The antenna of claim 1 wherein the active element and ground elements comprise electrically conducting members having widths and thicknesses wherein the thickness of each element is substantially smaller than its width.

10. The antenna of claim 1 wherein the active element and ground elements each comprise a sheet of material.

11. The antenna of claim 10 wherein the ground elements are curved and all axes of curvature of the ground elements are parallel to a plane of the active element.

12. The antenna of claim 1 wherein the active element is substantially planar.

13. The antenna of claim 1 wherein the ground elements are curved.

14. The antenna of claim 13 wherein the ground elements each follow a semi-cubical parabolic curve.

15. The antenna of claim 13 wherein the ground elements each follow an arc.

16. The antenna of claim 13 wherein the ground elements each follow an exponential curve.

17. The antenna of claim 13 wherein the ground elements each follow an elliptical curve.

18. The antenna of claim 1 wherein the ground elements are each planar.

19. The antenna of claim 1 wherein the active and ground elements are surrounded by air.

20. The antenna of claim 1 wherein the active and ground elements are surrounded by a gas other than air.

21. The antenna of claim 1 wherein the active and ground elements are surrounded by a liquid having dielectric properties different from air.

22. The antenna of claim 1 wherein the active and ground elements are in a vacuum.

23. The antenna of claim 1 wherein the active and ground elements are embedded in a solid dielectric material.

24. The antenna of claim 1 wherein the ground elements comprise resiliently flexible sheets and the antenna comprises a member holding each of the resiliently flexible sheets in a curved configuration.

25. The antenna of claim 1 wherein the ground elements each comprise a flexible sheet, the antenna comprises a curved form corresponding to each of the ground elements and each of the ground elements is held to follow the curved form.

26. The antenna of claim 25 wherein each of the curved forms makes contact with the corresponding ground element only at discrete spaced apart areas.

27. The antenna of claim 1 comprising a coaxial connector having a center conductor and a shield conductor wherein the active element is mounted directly to the center conductor and the ground elements are mounted to the shield conductor.

28. The antenna of claim 1 having a mean return loss of less than −3 dB and a deviation about the mean return loss of less than 10 dB over a bandwidth of 5 GHz.

29. The antenna of claim 1 wherein medial ends of ground elements are flared.

30. The use of an antenna as described in claim 1 for transmitting electromagnetic radiation at one or more frequencies in the range of 20 MHz to 100 GHz.