Cross-link antenna system

#The present invention relates to communications among a plurality of spacecraft using determined receive beams.

#Differently configured antennas have been developed to achieve desired objectives. In one area of application, antennas have been devised for use with spacecraft that orbit the earth. The orbiting spacecraft using their antennas are able to gather and/or process information, such as data related to events or conditions on the earth's surface.

#In one specific class associated with antennas that orbit the earth, there are cross-link antenna systems which have been configured for communication and/or navigation purposes. These cross-link antenna systems include the capability of providing communications among a plurality of spacecraft. A particular type of cross-link system includes global positioning system (GPS) satellites. The GPS is used to provide central calibration of all spacecraft in the particular constellation to the same time reference. In addition, this cross-link system sends a given signal from one spacecraft to all other spacecraft in the constellation to allow dissemination of information to one or more of the spacecraft that is in view of a part of the earth that is of current interest. Known cross-link antenna systems in the GPS constellation use hemispherical patterns in both receive and transmit modes during communications among the satellites of the constellation. Each satellite transmits in a prescribed time bin of 1.5 seconds and all other spacecraft receive this information during that time interval. This scheme has a drawback in that the antennas with the satellites of the GPS have relatively small gain. This limits the data range and more importantly makes this cross-link system susceptible to interference due to poor link margin.

#FIG. 1 diagrammatically illustrates the prior art cross-link system in which the same hemispherical receive pattern is employed by all beam receiving spacecraft to receive the transmit beam from the transmitting spacecraft;

#FIG. 2 diagrammatically illustrates the cross-link system of the present invention in which one or more spacecraft in the constellation generate a receive beam in the direction of the transmit beam;

#FIG. 3 illustrates a block diagram of major components of an antenna apparatus that is used with a spacecraft of the present invention;

#With reference to FIG. 2, a constellation of a number of spacecraft 100, 102, 104, 106, 110 is diagrammatically illustrated. Each of the spacecraft 100-110 includes an antenna apparatus 120, 122, 124, 126, 130, respectively, which is capable of selectively generating a transmit beam or a receive beam. During certain predetermined time bins or intervals, one of the spacecraft 100-110 acts as a transmit spacecraft and each of the other spacecraft acts as a receive spacecraft.

#One or more of the antennas apparatuses 120-130 is configured to generate a receive beam that is directed to the transmit spacecraft and its transmit beam. For another time interval, when there is a different transmit spacecraft, each of the one or more other spacecraft can generate their receive beams in the direction of the then current transmit spacecraft.

#In the embodiment of the FIG. 2, five spacecraft are illustrated, although any number of spacecraft could be utilized. The five illustrated spacecraft 100-110 include the current transmit spacecraft 100 and the remaining four spacecraft 102, 104, 106, 110 that are in the process of receiving the transmit beam using their receive beams. Illustrated in the embodiment of FIG. 2 is the aspect that not all of the antenna apparatuses in the constellation need be configured to generate a directed receive beam. Prior art antenna apparatus with their associated spacecraft can also be included in the constellation. Such prior art spacecraft typically generate a fixed receive beam, such as a hemispherical pattern. In the embodiment of FIG. 2, the spacecraft 106 including its antenna apparatus 126 is not configured to be able to generate a directed receive beam. Instead, its receive beam is hemispherical in shape and has that same shape and direction, regardless of which of the other spacecraft is the current transmit spacecraft when the spacecraft 106 is in its receive mode. With respect to the other receive spacecraft 102, 104, 110, the antenna apparatuses 122, 124, 130 thereof can generate the desired, directed receive beam. As can be appreciated, such a receive beam is different from the hemispherical pattern and different from other, less directed beam patterns including omnidirectional patterns. FIG. 2 also illustrates diagrammatically the noise or other interference that can emanate from the earth (E) during any transmission by the current transmit spacecraft and the reception by the current receive spacecraft. The directed receive beams can be generated or controlled to at least significantly reduce the unwanted effects of such interference and, in some cases, minimize the effects of such interference.