Variable pitch angle, axial mode helical antenna

• US 5,892,480 A
• Filed: 04/09/1997
• Issued: 04/06/1999
• Est. Priority Date: 04/09/1997
• Status: Expired due to Fees

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Killen, William D.
• Primary Examiner(s): KIM, ROBERT H
• Application Number:
  US08/838,546
• Time in Patent Office: 727 Days
• Field of Search: 343/895, 343/713, 343/715, 343/752
• US Class Current: 343/895
• CPC Class Codes: H01Q 1/362 for broadside radiating helical antennas

Abstract

Optimization of the exchange of energy between a free space wave and current flowing in the conductive helix of an axial mode, helical antenna is achieved by varying the pitch angle of successive turns of the antenna along the axis of the antenna, from a relatively small pitch angle at the base, feed location of the antenna, to a relatively large value at the distal end of the antenna. Pitch angles of successive turns of the antenna are varied in a non-linear manner to correspond to the non-linear manner in which the phase velocity of a wave propagating through the antenna varies relative to the phase velocity of a free space electromagnetic wave. For the case of an axial mode, helical antenna operating at C-band, the pitch angle of said antenna may be varied between 3-8 degrees at the antenna feed point to a 20-30 degrees at its free space-interfacing distal end. The variable pitch angle antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions, one of which has a peak gain slightly less than the other. This dual peak gain behavior permits application design trade off between a smaller sized antenna with slightly reduced performance versus a larger sized antenna with slightly higher performance.

Claims

1. A multi-turn axial mode, helical antenna for interfacing an electromagnetic wave having a wavelength less than the axial length of said helical antenna, which extends from a feed location at a base of said helical antenna to a distal end of said helical antenna, said helical antenna comprising a helical winding having the same prescribed diameter along said axial length of said helical antenna, and wherein spacings between and pitch angles of successive turns of said helical winding vary along a line parallel to said axis of said helical from first respective spacing and phase angle values at said feed location, to second respective spacing and phase angle values at said distal location, which are larger than said first respective spacing and phase angle values.

2. A multi-turn axial mode, helical antenna according to claim 1, wherein values of said spacings and pitch angles of successive turns of said helical winding vary in a manner that matches the phase velocity of a free space electromagnetic wave interfaced with said antenna with the phase velocity of a wave traveling through said antenna.

3. A multi-turn axial mode, helical antenna according to claim 1, wherein values of said pitch angles of successive turns of said helical winding vary in a non-linear manner along said axial length of said helical winding.

4. A multi-turn axial mode, helical antenna according to claim 1, wherein values of said spacings of successive turns of said helical winding vary from a value on the order of a half-wavelength at said distal end of said helical winding to a quarter wavelength at said feed location of said helical winding.

5. A multi-turn axial mode, helical antenna according to claim 1, wherein said antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions.

6. A multi-turn axial mode, helical antenna according to claim 1, wherein said pitch angles vary from a value on the order of 3-8 degrees at said feed location to a value on the order of 20-30 degrees at said distal end of said helical winding.

7. A multi-turn axial mode, helical antenna according to claim 1, wherein said helical winding has a pitch angle on the order of 23-26 degrees at said distal end thereof.

8. A multi-turn axial mode, helical antenna according to claim 1, wherein said electromagnetic wave is circularly polarized.

9. A multi-turn axial mode, helical antenna according to claim 1, wherein said helical winding comprises a bifilar helix.

10. A method of improving the efficiency and gain of a multi-turn axial mode, helical antenna for interfacing an electromagnetic wave having a wavelength less than the axial length of said helical antenna, which extends from a feed location at a base of said helical antenna to a distal end of said helical antenna, comprising the steps of:

(a) configuring said helical antenna as constant diameter helical winding along said axial length thereof; and

(b) varying spacings between and pitch angles of successive turns of said helical winding vary along a line parallel to said axis of said helical from first respective spacing and phase angle values at said feed location, to second respective spacing and phase angle values at said distal location, which are larger than said first respective spacing and phase angle values.

11. A method according to claim 10, step (b) comprises varying values of said spacings and pitch angles of successive turns of said helical winding in a manner that matches the phase velocity of a free space electromagnetic wave interfaced with said antenna with the phase velocity of a wave traveling through said antenna.

12. A method according to claim 10, wherein step (b) comprises varying said pitch angles of successive turns of said helical winding in a non-linear manner along said axial length of said helical winding.

13. A method according to claim 10, wherein step (b) comprises varying said spacings of successive turns of said helical winding from a value on the order of a half-wavelength at said distal end of said helical winding to a quarter wavelength at said feed location of said helical winding.

14. A method according to claim 10, wherein said helical antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions.

15. A method according to claim 10, wherein step (b) comprises varying said pitch angles from a value on the order of 3-8 degrees at said feed location to a value on the order of 20-30 degrees at said distal end of said helical winding.

16. A method according to claim 10, wherein step (b) comprises configuring said helical winding to have a pitch angle on the order of 23-26 degrees at said distal end thereof.

17. A method according to claim 10, wherein said electromagnetic wave is circularly polarized.

18. A multi-turn axial mode, helical antenna for interfacing an electromagnetic wave having a wavelength less than the axial length of the antenna, said helical antenna comprising a helical winding having a prescribed diameter said axial length thereof, and wherein spacing between any two successive turns of said helical winding along a first line parallel to said axial length of said helical winding differs from spacing between any two other successive turns along a second line parallel to said axial length of said helical winding, so that successive turns of said antenna have successively different pitch angles.

19. A multi-turn axial mode, helical antenna according to claim 18, wherein spacings between and thereby pitch angles of successive turns of said helical winding vary in a non-linear manner that matches the phase velocity of a free space electromagnetic wave interfaced with said antenna with the phase velocity of a wave traveling through said antenna.

20. A multi-turn axial mode, helical antenna according to claim 18, wherein said helical winding comprises a bifilar helix.