Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-03-21
2004-07-06
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S081000
Reexamination Certificate
active
06759978
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications among a plurality of spacecraft using determined receive beams.
BACKGROUND OF THE INVENTION
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.
With reference to
FIG. 1
, the prior art cross-link system is diagrammatically illustrated. The prior art system includes a number of spacecraft and, at any instance in time, one of the spacecraft can be characterized as the transmitting spacecraft
20
and the other spacecraft of the constellation can be characterized as the receiving spacecraft
24
a
,
24
b
,
24
c
,
24
d
. As schematically represented, the transmitting spacecraft
20
sends a multi-directional transmit beam when it is in its transmit mode. Each of the other spacecraft of the constellation, the receiving spacecraft
24
a
-
24
d
, is in its receive mode and each generates or outputs a receive beam for receiving the transmit beam, during the time interval that the transmitting spacecraft
20
is in its transmit mode. As also represented schematically, each of the receiving spacecraft
24
a
-
24
d
generates the same shape or configuration of receive beam, namely, the hemispherical pattern. Further depicted in
FIG. 1
is the ever present interference or noise emanating from the earth (E). This noise, which is picked up by the hemispherical patterns of the receive beams of the receiving spacecraft, negatively impacts the transmission being sent by the transmitting spacecraft
20
. In accordance with this prior art system, once the transmitting spacecraft
20
has finished with its transmit mode, with the prescribed time bin for that spacecraft ending, another spacecraft in the constellation enters its transmit mode. More specifically, one of the previously identified receiving spacecrafts
24
a
-
24
d
now becomes the transmitting spacecraft. The other spacecraft including the former transmitting spacecraft are placed in their receive modes to receive the transmit beam from this next transmitting spacecraft during communications, such as establishing the same time reference for each of the spacecraft in the constellation. For each time bin with a different transmitting spacecraft, the same non-configurable beam reception patterns are generated by the receiving satellite that have unwanted results including signal interference and data range limitations.
SUMMARY OF THE INVENTION
In accordance with the present invention, a cross-link system is provided that includes a plurality of spacecraft. Each of the spacecraft has an antenna. One or more of these antennas can point or direct their receive beams in the direction of the transmit beam emanating from the current transmit antenna of the transmit spacecraft. This control of the receive beams improves the link margin due to the increased gain of such currently receiving antennas and their lower sidelobes in the unwanted direction(s). Control over beam direction can be done either adaptively or on a fixed basis.
With respect to the one or more antenna apparatuses, that are part of spacecraft in the constellation, and which can control its receive beam in the direction of the current transmit beam, each such antenna apparatus can include a beam controller, phase shift circuitry, a plurality of low noise amplifiers (LNAs), a number of antenna or radiating elements, a combiner and a receiving radio. The beam controller includes at least one processor involved with outputting signals that control the amplitudes and phases of the antennas elements. The phase shift circuitry preferably includes a number of phase shifters. Each of the different phase shifters electrically communicates with a different one of the LNAs. Each LNA electrically communicates with a particular one of the antenna elements. The control signals from the beam controller enable different signal amplitudes to be individually applied to the antenna elements after amplification by its associated LNA. Each of the phase shifters can be separately activated at different times. Depending on the direction of the receive beam for the antenna of a particular spacecraft, a desirably directed receive beam can be output by that antenna apparatus, namely, in the direction of the transmit beam from the transmit antenna that is currently generating the transmit beam. A combiner signal is developed in the combiner, which is a combination of the signals received using the antenna elements, LNAs and phase shifters due to the generated receive beam. The combiner signal is output to the receiving radio. In one embodiment, the receiving radio is involved with a determination related to the signal-noise ratio (SNR) of the combiner signal. The SNR of the combiner signal is useful in ascertaining a maximum, preferred or desired gain of the receive beam for a particular transmit beam.
Regarding communications involving a spacecraft of the particular constellation when one of them is in a transmit mode and the other spacecraft are in a receive mode, a description is provided related to a communication between the current transmit spacecraft and one of the spacecraft that is receiving the transmit beam from this transmit spacecraft. As can be appreciated, this description also applies to other spacecraft in the constellation that are generating their own receive beams to receive the current transmit beam. This description is also applicable to subsequent transmit beams from other spacecraft in the constellation when they are caused to send a transmit beam during a specified time bin.
Important to controlling a first receive beam associated with a first antenna of a first spacecraft are making determinations related to locations of each of the first receive spacecraft and the first transmit spacecraft that has the first transmit antenna outputting the first transmit beam. Additionally, location information is obtained related to the antenna elements of the first receive antenna.
With regard to the location of the first receive spacecraft, first and second receive values are obtained. Preferably, the first and second receive values are angle related. In one embodiment, the first receive value relates to a first angle in one plane, such as the elevation plane. The second receive value relates to a second angle in the azimuth plane. First and second attitude values are also obtained related to the attitude of the first receive spacecraft. The first attitude value relates to one attitude angle in elevation and the
Ball Aerospace & Technologies Corp.
Phan Dao
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