Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2000-03-21
2001-03-06
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S757000, C343S765000
Reexamination Certificate
active
06198455
ABSTRACT:
BACKGROUND
The present invention relates generally to antennas for use on spacecraft, and more particularly, to variable beamwidth antenna systems designed for use on spacecraft.
The present invention relates to improvements in offset Gregorian reflector antenna systems for use on communication satellites. Due to unpredictability of communication traffic, it is desirable that the beamwidth of the antenna radiation pattern be changeable when the spacecraft is on orbit.
Accordingly, it would be advantageous to have improved variable beamwidth antenna systems that may be used on a spacecraft that has a changeable beamwidth.
SUMMARY OF THE INVENTION
The variable beamwidth antenna system comprises a main reflector, a reflector displacement mechanism, a subreflector, a feed horn, and a feed horn displacement mechanism. The reflector displacement mechanism can place the main reflector at any desired location, while the feed displacement mechanism can place the feed horn at any desired location. More specifically, the main reflector displacement mechanism controls the spacing between the main reflector and the subreflector; while the feed displacement mechanism controls the spacing between the feed and the subreflector.
To implement the present invention, two mechanical movements are required. First, the RF feed horn and the subreflector are moved closer together. Second, the main reflector is moved away from the subreflector. Alternatively, the subreflector is moved closer to the RF feed horn, and the main reflector is moved away from the subreflector.
Two mechanical movements are not independent. They are related by
y
=
d
2
x
c
2
-
x
(
c
+
d
)
where “x” is the distance of RF feed horn displacement, and “y” is the distance of the main reflector displacement.
When x=y=0, the antenna arrangement is in the focused condition. Under the focused condition, the focal point of the paraboloidal main reflector is coincident with one of the foci of the elliptical subreflector, and the feed horn is located at the other focus of the subreflector. The terms “c” and “d” in the above equation are the distance between the RF feed horn and the subreflector, and the distance between the focal point of the main reflector and subreflector, respectively, when the antenna is in focus.
A reduced-to-practice embodiment of the present variable beamwidth antenna has 3 dB beamwidth that can be changed while the spacecraft is on orbit by proper displacements of any two components among the main reflector, the subreflector and the feed.
REFERENCES:
patent: 4355314 (1982-10-01), Ohm
patent: 4866457 (1989-09-01), Hogg
patent: 6043788 (2000-03-01), Seavey
Float Kenneth W.
Phan Tho
Space Systems Loral, Inc.
Wong Don
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