Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2001-02-09
2003-02-18
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S7810CA, C343S772000
Reexamination Certificate
active
06522305
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microwave antennas. Certain aspects of this invention are applicable to only dual-reflector antennas, and other aspects are applicable to both single-reflector and dual-reflector antennas.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a dual-reflector microwave antenna is provided with a main reflector having a shape that is a portion of a paraboloid generated by revolution of a parabola around having a single, common axis of rotation and symmetry; a primary feed extending along the axis of the main reflector on the concave side of the main reflector and having an aperture spaced away from the main reflector; and a subreflector located beyond the end of said primary feed for reflecting radiation from the main reflector into the primary feed and for reflecting radiation from the primary feed onto the main reflector, the subreflector having an image-inverting surface configuration that has a ring focus located between the main reflector and the subreflector and extending around the axis of the main reflector, the ring focus having a diameter at least as large as the diameter of the aperture of the primary feed. In a preferred embodiment, the subreflector has a shape that is a portion of an ellipsoid generated by revolution of an ellipse around the axis of the main reflector, a first focal point of the ellipse being located on the axis and a second focal point of said ellipse being offset from the axis so that revolution of the ellipse around the axis forms a focal ring extending around the axis. The patterns produced by this antenna can be improved by providing an absorber-lined shield around the periphery of the subreflector The return loss of this and other dual-reflector antennas may be reduced by providing a dielectric or electrically conductive element between the primary feed and the subreflector.
In accordance with another aspect of the invention, a reflector-type microwave antenna is provided comprising a reflector having a shape that is a portion of at least one paraboloid and having an axis of symmetry; a primary feed extending along the axis; and a shield extending around the outer periphery of the reflector and projecting from the reflector in the same direction as the energy being transmitted by the reflector from the primary feed, and a band of dielectric or conductive material extending around at least a portion of the inner surface of the shield for reducing the return loss of the antenna. To improve the patterns produced by the antenna, the shield may be lined with absorber material, preferably only on the side portions to improve the horizontal pattern without significantly increasing either the gain loss or the cost of the antenna.
In accordance with a further aspect of the invention, a reflector-type microwave antenna is provided comprising a reflector having a shape that is a portion of at least one paraboloid and having an axis of symmetry; a primary feed extending along the axis; and a shield extending around the outer periphery of the reflector and projecting from the reflector in the same direction as the energy being transmitted by the reflector from the primary feed, and a shield of absorber material extending around the outer periphery of at least an end portion of the primary feed. In a preferred embodiment of this aspect of the invention, the antenna is a dual-reflector antenna that includes a subreflector of the type described above, and the shield of absorber material has an outer diameter that is smaller than the diameter of the ring focus of the subreflector.
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Andrew Corporation
Ho Tan
Jenkens & Gilchrist
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