Horn reflector antenna with absorber lined conical feed

• US 5,317,328 A
• Filed: 04/02/1984
• Issued: 05/31/1994
• Est. Priority Date: 04/02/1984
• Status: Expired due to Fees

• Current Assignee: Tripoint Global Microwave Inc.
• Original Assignee: Gabriel Electronics, Inc. (General Dynamics Corporation)
• Inventors: Allen, Daniel C.
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US06/596,100
• Time in Patent Office: 3,711 Days
• Field of Search: 343/786, 343/840, 343/781 R, 343/912
• US Class Current: 343/786
• CPC Class Codes: H01Q 17/001 for modifying the directional characteristic of an aerial
• CPC Class Codes: H01Q 19/132 Horn reflector antennas; Off-set feeding

Abstract

A conical horn microwave antenna has a reflector positioned at the large end of a conical feed horn which has the side walls of the horn wider than the projected effective area of the reflector such that microwave absorber material lining the feed horn does not obstruct wave propagation between the feed horn and the effective reflector area.

Claims

1. In a horn reflector antenna which has a housing formed by a cone and a shroud the axes of which intersect at approximately 90°

, the axis of said shroud being the radiation pattern beam axis of the antenna and the axis of said cone being the feed axis, and a reflector positioned within said housing at an angle to the beam axis and the feed axis to reflect microwave energy between an aperture on the beam axis and an off-set feed horn at the apex of said cone wherein said aperture is the open end of said shroud and approximately the size of the full area of said reflector projected on said beam axis, said cone extending from the mouth of said feed horn to intersect said shroud to form a conductive housing closed except for said aperture, the improvement which comprises making the inner diameter of said cone larger through out its axial length than the projected full area of said reflector to the mouth of said feed horn; and

microwave absorber material lining the inner wall of said cone over substantially its entire length from said feed horn to said shroud, said material having thickness at any point in the cone no greater than the spacing between said inner diameter and the periphery of the projected full area of said reflector to said mouth to avoid blocking microwave energy, passing between said feed horn and the full area of said reflector, said absorber improving the radiation pattern by its effect on the microwave energy passing through the cone without significant gain loss due to absence of absorber in the path of said energy.

2. The antenna according to claim 1 in which said inner diameter is spaced a fixed distance from the periphery of the projected area of said reflector along said feed axis.

3. The antenna according to claim 2 in which said absorber material is a uniform layer having a thickness approximately equal to said fixed distance.

4. The antenna according to claim 1 in which said inner diameter is tapered at a greater angle than the projection of the periphery of said reflector to said mouth thereby progressively increasing said spacing from the narrow end of said cone toward said reflector.

5. The antenna according to claim 4 in which said absorber material has progressively increased thickness corresponding approximately with said increasing spacing.

6. In a horn reflector antenna in which a conductive housing is formed by a cone and cylinder intersecting with their axes at approximately 90°

for enclosing a parabolic reflector that is located at the intersection of said axes and inclined at approximately 45°

thereto to provide an effective area that reflects microwave energy between an aperture on the axis of said cylinder and the focus of said paraboloid on the axis of said cone, the size of said aperture being the projected effective area of said reflector on the axis of said cylinder, the improvement which comprises;

forming the inner wall of said cone to lie outside the lines of projection from said focus to said effective area of said reflector and lining said inner wall with microwave absorber material having thickness which substantially avoids blocking the microwave energy passing through said cone between said focus and said effective area of said reflector.

7. The antenna according to claim 6 wherein said microwave absorber material comprises a plurality of bands of absorber progressively increasing in thickness to approximately fill the volumn between said inner wall and said lines of projection.

8. A horn reflector antenna comprising:

a paraboloidal reflector forming a paraboloidal reflecting surface for transmitting and receiving microwave energy;

a horizontal conductive cylinder with means for mounting said reflector at approximately 45°

to the axis of said cylinder, the open end of said cylinder forming the aperture of said antenna;

a conical conductive feed horn, extending from approximately the focus of said paraboloidal reflecting surface to an intersection with said cylinder for guiding microwave energy to said reflector;

a lower end portion of the inside surface of said conical horn being formed by a smooth metal wall above which the diameter of said conical horn is wider than necessary to illuminate the full area of said reflector with energy from said focus;

a lining of microwave absorber material completely lining said conical feed horn from the upper edge of said lower end portion to said intersection with said cylinder, the thickness of said absorber being selected to recess the absorber from the path of energy passing between the full area of said reflector and said focus to reduce the gain loss which is otherwise produced by absorber in said path while improving the radiation pattern by the operation of the absorber lining on energy transmitted through the conical horn.