Compact low sidelobe antenna and feed network

1. An antenna comprising:

a primary reflector having a ring focus;

a feed body along an axis of the primary reflector, the feed body including a circular waveguide coaxial with the axis of the primary reflector;

a sub-reflector disposed facing an end of the circular waveguide;

a generally cylindrical stem extending from a center of the sub-reflector into the circular waveguide to form a section of annular waveguide; and

a sub-reflector support that mechanically connects a perimeter of the sub-reflector and an outside surface of the feed body,

wherein the sub-reflector, the stem, and the feed body are collectively configured to couple microwave energy between the annular waveguide and the primary reflector.

2. The antenna of claim 1 , wherein the sub-reflector comprises:

a generally conical center portion; and

a curved outer portion.

3. The antenna of claim 2 , comprising a choke groove around a perimeter of the sub-reflector.

4. The antenna of claim 2 , wherein the curved outer portion has a warped parabolic shape.

5. The antenna of claim 2 , wherein the curved outer portion is defined by the equation:

4 F ( z+αz 2 )=( r−−r 0 ) 2 +β( r−r 0 ) 4   (1)

wherein

F=a focal length of the warped parabolic shape,

z=a distance along the antenna axis measured from the vertex of the parabolic curve,

r=a radial distance from the antenna axis,

r 0 =a radial distance from the axis of the primary reflector to a local axis of the warped parabolic shape, and

α and β=warping coefficients.

6. The antenna of claim 1 , further comprising a dielectric stem support to support the stem centered within the circular waveguide.

7. The antenna of claim 1 , further comprising a plurality of ribs extending radially outward from the feed body.

8. The antenna of claim 7 , wherein

the plurality of ribs includes an upper rib closest to the sub-reflector, and

a portion of the sub-reflector support is adjacent to and supported by the upper rib.

9. The antenna of claim 1 , wherein the sub-reflector support is configured to create a seal between the sub-reflector and the feed body.

10. The antenna of claim 1 , wherein

the feed body and the sub-reflector are fabricated from aluminum or an aluminum alloy, and

the sub-reflector support is fabricated from a low-loss dielectric material having a thermal expansion coefficient similar to that of aluminum.

11. The antenna of claim 10 , wherein the sub-reflector support is fabricated from a glass-filled polyphenylene sulfide plastic material.