DISH ANTENNA HAVING SWITCHABLE BEAMWIDTH

• US 3,866,233 A
• Filed: 09/10/1973
• Issued: 02/11/1975
• Est. Priority Date: 09/10/1973
• Status: Expired due to Term

• Current Assignee: Richard F. Schmidt
• Original Assignee: Richard F. Schmidt
• Inventors: Schmidt, Richard F.
• Primary Examiner(s): Lieberman, Eli
• Application Number:
  US05/395,868
• Time in Patent Office: 519 Days
• Field of Search: 343/779,781,840,761,837
• US Class Current: 343/761
• CPC Class Codes: H01Q 25/002 providing at least two patterns of different beamwidth; Variable beamwidth antennas
• CPC Class Codes: H01Q 3/16 for varying relative position of primary active element and a reflecting device

Abstract

A switchable beamwidth antenna includes a concave parabolic main reflecting dish which has a central circular region and a surrounding coaxial annular region. A feed means selectively excites only the central region of the main dish via a truncated subreflector for wide beamwidth or substantially the entire main dish for narrow beamwidth. In one embodiment, the feed means comprises a truncated concave ellipsoid subreflector and separate feed terminations located at two foci of the ellipsoid. One feed termination directly views all of the main dish while the other feed termination, exciting the main dish via the subreflector, excites only the central region because of the subreflector truncation. In the another embodiment, the feed means comprises one feed termination and a convex hyperboloid subreflector via which the feed excites the main dish. The subreflector has a fixed central region via which the feed termination excites the central region of the main reflector and a retractable surrounding annular region via which the feed termination excites the annular region of the main reflector. Beamwidth switching is effected by retracting the annular region to truncate the subreflector.

Claims

1. A switchable beamwidth antenna having a wide beamwidth state and a narrow beamwidth state at a single predetermined frequency, said beamwith state being responsive to a beamwidth selection command source comprising:

a main reflecting dish having a boresight axis and a direction of view along said axis, wherein said dish may be divided with an imaginary contour coaxial with the boresight axis into a central portion and an outer portion bordering the central portion; and

single frequency means responsive to the beamwidth selection command source, exciting substantially only the central portion of the main dish in the wide beamwidth state, and for exciting both the central and outer portions of the main dish in the narrow beamwidth state, said exciting means including a reducible subreflector defining in the reduced state a truncated subreflector for exciting only the central portion of the main dish so as to achieve the wide beamwidth state.

2. The antenna of claim 1 wherein said exciting means comprises:

a feed positioned to view in the same direction as the main dish;

a subreflector facing the main dish, said subreflector comprising the truncated subreflector which is a fixed reflecting central portion via which the central portion of the main dish is excited by the feed and a retractable outer reflection portion via which the outer central portion of the main dish is excited by the feed only in the narrow beamwidth state; and

means for retracting the outer portion of the subreflector, said means including an actuator responsive to the beamwidth selection command.

3. The antenna of claim 2 wherein said main dish is a concave paraboloid having a focal point in front of the dish;

said subreflector is a convex hyperboloid having first and second conjugate foci coaxial with the main dish, and said hyperboloid is located with the first focus at the main dish focal point;

said outer retractable portion of said subreflector is annular in shape and continuous with said central portion prior to its retraction; and

said suBreflector is coaxial with the dish and located at second focus.

4. The antenna of claim 3 wherein said retracting means comprises means for axially moving the outer portion of the subreflector.

5. The antenna of claim 4 wherein said retracting means comprises means for axially moving said subreflector at least four wavelengths at said single frequency.

6. The antenna of claim 3 wherein said retracting means comprises means for rotating the outer portion of the reflector surface about an axis substantially perpendicular to the main dish axis.

7. The antenna of claim 3 wherein said outer portion of said subreflector is an iris annulus having a retracted position overlapping the central portion of the subreflector and wherein said retraction means comprises a motor for axially rotating the iris.