Single frequency, two feed dish antenna having switchable beamwidth

• US 3,927,408 A
• Filed: 10/04/1974
• Issued: 12/16/1975
• Est. Priority Date: 10/04/1974
• Status: Expired due to Term

• Current Assignee: Richard F. Schmidt
• Original Assignee: Richard F. Schmidt
• Inventors: Schmidt, Richard F.
• Primary Examiner(s): Gensler, Paul L.
• Application Number:
  US05/512,825
• Time in Patent Office: 438 Days
• Field of Search: 343/779,781,837,840
• US Class Current: 343/779
• CPC Class Codes: H01Q 25/002 providing at least two patterns of different beamwidth; Variable beamwidth antennas
• CPC Class Codes: H01Q 3/245 in the focal plane of a focussing 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 the embodiment shown, 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.

Claims

1. A switchable beamwidth antenna having a wide beamwidth state and a narrow beamwidth state at a single predetermined frequency, said beamwidth 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 at said single predetermined frequency substantially only the central portion of the main dish in the wide beamwidth state, and exciting both the central and outer portions of the main dish in the narrow beamwidth state, said single frequency means including in the wide beamwidth state a truncated subreflector positioned to excite the main dish and further including a first feed positioned to view said truncated subreflector the truncated subreflector having a concave reflecting surface facing the main dish, being positioned to be excited by the first feed, and being of a size that only the central portion of the main dish may be viewed by the first feed via the subreflector, said single frequency means including in the narrow beamwidth state a second feed located between the main reflector and the subreflector and positioned to directly view substantially all of the main dish. A radio frequency conduit coupled to a microwave source or receiver and a radio frequency switch means responsive to the beamwidth selection command for coupling the radio frequency conduit to the first feed in the wide beamwidth state and to the second feed in the narrow beamwidth state.

2. An electronically selectable beamwidth antenna comprising:

a concave paraboloid main reflector having an axis and a focal point, and where said main reflector has a central circular region and an outer annular region bordering the central region;

a concave ellipsoid subreflector coaxial with and facing the concave main reflector, the subreflector having a first foCus substantially coincident with the main reflector focal point for directly exciting the main reflector and a second focus on the axis for exciting the main reflector via the subreflector, the subreflector being of such size that only the central portion of the main reflector can be viewed via the subreflector;

first feed means, located at the first focus of the subreflector for directly exciting the main reflector at a predetermined frequency;

second feed means, located at the second focus of the subreflector for exciting, via the subreflector, only the central portion of the main reflector at said predetermined frequency; and

switch means for operatively selecting the first or second feed means.