US 4,232,321 AGranted

Multiple beam satellite antenna with preferred polarization distribution

AssigneeBell Telephone Laboratories, Incorporated

InventorEdward A. Ohm

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Abstract

Microwave energy feed elements for launching essentially linearly polarized beams in a satellite communications system are oriented in the satellite's antenna so that the polarization directions of the feed elements form a rim and spoke configuration. The vertical polarizations are arranged to extend radially from a point on the antenna's focal surface which images the point on the surface of the celestial body directly below the satellite. Horizontal polarizations are arranged concentrically about the subsatellite image point. Electromagnetic energy launched from the feed elements will reach the surface of the earth at planes of incidence which are locally vertical and horizontal, thereby minimizing cross-polarization coupling between the orthogonally polarized signals due to such energy passing through precipitation.

Claims7

Dependent claims

In a satellite communications system, a method of transmitting electromagnetic energy from a satellite to a remote receiving area on the surface of a celestial body which results in a reduced amount of cross-polarization coupling along the transmission path, the satellite being in orbit directly above a subsatellite point (51) on the celestial body and comprises an antenna arrangement comprising (a) at least a main reflector aperture, a feed and a focal surface disposed transversely about the feed axis, the focal surface being comprised of a plurality of focal points, each of which corresponds to a respective point in the remote receiving area and a projection of the subsatellite point (50) on the focal surface and (b) plural feed elements disposed on the focal surface, the method comprising the step of:

(a) energizing one or more feed elements (e.g., 113, 114) for transmitting at least one beam of electromagnetic energy comprising any combination of a first and a second direction of essentially linear polarization which are orthogonal to one another toward the portions of the receiving area on the celestial body associated with the particular points on the focal surface where the energized feed elements are disposed,
CHARACTERIZED IN THAT
the method comprises the further step of:
(b) in performing step (a), energizing the one or more feed elements for transmitting the at least one beam of electromagnetic energy so that when the first direction of polarization is used by any particular one of the energized feed elements, the first direction is aligned parallel to a line on the focal surface connecting the corresponding subsatellite point and the point where the particular feed element is disposed (60-66), and when the second direction of polarization is used by any particular one of the feed elements, the second direction is aligned orthogonal to the line on the focal surface connecting the corresponding subsatellite point and the point on the focal surface where the particular feed element is disposed (70-73).

1 more element

In a satellite communication system of the type wherein a predetermined zone on the surface of a celestial body in the far field is illuminated by a plurality of electromagnetic energy beams produced by an array of feed elements disposed near the focal surface of a satellite antenna, adjacent ones of which feed elements illuminate respectively associated contiguous areas within the predetermined zone and capable of launching electromagnetic energy in any combination of first and second essentially linear, orthogonal directions of polarization, an arrangement for producing a plurality of composite beams, each of which is composed of the combined illumination of a cluster (e.g., 10) of plural, adjacent feed elements (e.g., 113, 112, 114),

CHARACTERIZED IN THAT
the arrangement comprises
means capable of energizing each feed element in a cluster (e.g., 10) to launch a respective beam of electromagnetic energy so that when the first direction of polarization is used by any particular one of the energized feed elements, the first direction is aligned parallel to a line on the focal surface connecting an image of a subsatellite point directly below the satellite and the point where the particular feed element is disposed (e.g., 60), and when the second direction of polarization is used by any particular one of the feed elements, the second direction is aligned orthogonal to the line on the focal surface connecting the imaged subsatellite point and the point on the focal surface where the particular feed element is disposed (e.g., 71).

Dependencies are inferred from the claim text.