Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
1998-08-21
2001-10-16
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S823000, C343S91100R, C343S91100R
Reexamination Certificate
active
06304225
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to satellite antenna systems and more particularly to an improved lens system for an antenna system.
BACKGROUND OF THE INVENTION
Communications networks employ satellites operating in geosynchronous orbits in combination with terrestrial facilities such as land lines, microwave repeaters, and undersea cables to provide communications over vast areas of the earth. Geosynchronous satellites and terrestrial facilities are both expensive to install and to maintain and thus are not a cost effective means of increasing network capacity. In addition, geosynchronous satellites which operate at an altitude of 22,300 miles above the earth are unsuitable for supporting cellular service because of the extremely high power levels that would be required to communicate with satellites at that altitude.
More recently, constellations of low earth orbit (LEO) satellites have been proposed and are being developed as a cost effective means for providing increased capacity and supporting cellular and broadband data service for communications networks. In such a constellation, the satellites are divided into a number of orbital planes. Because low earth orbit satellites move rapidly with respect to the earth, each orbital plane includes a number of satellites that maintain continuous coverage for underlying cells defined on the surface of the earth. A footprint of cells represent the coverage region for each satellite.
Low earth orbit satellites utilize antennas which form a cluster of beams each assigned a ground-based cell. Due to the geometry of low earth satellites above the spherical surface of the earth, cells near the edges of the footprint have a much smaller angular size and closer angular spacing than cells near the center of the footprint. To accurately process signals from the cells, the antenna shapes each beam to match the angular size of its assigned cell. Existing beam shaping systems utilize phase shifting devices that greatly increase the complexity of the antenna and thus the cost of the satellite.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved lens system and method for an antenna are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed systems and methods. In particular, the present invention provides a lens system that uses non-uniform feed elements to shape beams to match the angular size of ground-based cells.
In one embodiment of the present invention, an antenna system includes a lens and a plurality of non-uniform feed elements. The non-uniform feed elements are coupled to the lens and operable to shape each of a plurality of beams to match an angular size of a ground-based cell assigned to the beam.
More specifically, in accordance with a particular embodiment of the present invention, the feed elements are non-uniform in that they are differently sized and variably spaced. The lens may be a spherical dielectric lens such as a Luneberg lens, a planar lens such as a Rotman lens, or other suitable lens.
Technical advantages of the present invention include providing an improved lens system. In particular, the lens system includes a plurality of non-uniform feed elements that shape beams to match the angular size of ground-based cells. Accordingly, the beams are shaped without phase shifting or other processing intensive methods. In addition, a substantially equal number of component beams are maintained for each ground-based cell. As a result, the total number of component beams needed to cover a cell footprint is reduced, which correspondingly reduces the number of feed elements and other components in the antenna beam-forming network. Accordingly, the complexity and cost of the antenna is reduced.
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Baker & Botts L.L.P.
Chen Shih-Chao
Raytheon Company
Wong Don
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