Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-02-04
2001-05-15
Trost, William G. (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S013300, C455S067700
Reexamination Certificate
active
06233433
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to in-orbit testing of communication satellites, and more particularly to in-orbit repeater testing from a single location on the ground of a satellite that broadcasts multiple downlink beams over a large geographic area.
2. Description of the Related Art
Multi-beam satellites are tested after a successful launch to verify the operation of the receive and transmit antennas and the electronic subsystems. A satellite repeater includes all of the electronics between the receive and the transmit antennas. The transponder includes a receive antenna, the electronics associated with the antenna, and one or more transmit antennas. As shown in
FIG. 1
, a single ground station
2
transmits an uplink signal
4
that contains broadcast information. A satellite
6
boosts the signal and distributes it to a plurality of narrow-beam transmit antennas that transmit spot beams
8
a
-
8
d
to different geographic regions
10
a
-
10
d
. The use of multiple downlink beams having smaller areas of coverage allows the broadcast information to be transmitted to individuals in specific areas, and reusing those same frequencies in other diverse areas.
In-orbit satellite test procedures are described in Egly et al, “In-Orbit Test of the First Hughes United States Direct Broadcast Satellite”,
International Journal of Satellite Communications
, Vol. 13, No. 5, September-October 1995, pages 301-312 and in Kasstan et al, “Recent Advances in ‘In-Orbit Testing’ of Communications Satellites”,
International Journal of Satellite Communications
, Vol. 13, No. 5, September-October 1995, pages 377-401. The tests disclosed in the articles do not sample the amplified downlink signal prior to transmission from the satellite.
A network of ground test stations are distributed throughout the different geographic regions
10
a
-
10
d
to receive the downlink signals and verify operation of the satellite subsystems. A test signal is transmitted from ground station
2
, amplified, and rebroadcast in downlink beams (
8
a
-
8
d
), which are sampled within their respective areas of coverage (
10
a
-
10
d
). In the example shown in
FIG. 1
, four test stations, one within each downlink beam, are required to receive downlink signals corresponding to the uplink test signal. Usually the ground test stations are portable so that the downlink signal can be measured from multiple points within the area of coverage. The power tests are conducted from a location within the downlink beam where the power level of the downlink signal is at or near maximum. The measured data is then combined with characteristics of the test signal and processed to verify operation.
A major disadvantage of the test method just described, is that the test is repeated at multiple ground test stations. As the number of channels increases, so does the number of tests which must be performed. Increasing the number of tests performed increases the time and cost of verifying the operation of the satellite.
SUMMARY OF THE INVENTION
The present invention provides a fast, low-cost apparatus and method for performing in-orbit repeater tests after launch. Positioning the satellite so that a receive antenna is aligned with the ground test station antenna provides the necessary link for testing the repeater. An uplink test signal is generated and transmitted from the single ground test station. The uplink test signal is converted to a downlink signal, amplified, and distributed to the transmit antennas fed by the receive antenna.
A directional coupler preceding each transmit antenna samples the downlink signal and a matrix of signal combiners and/or switches that selectively routes the sampled outputs to a single test amplifier. At one extreme, an extensive switch network routes each output test sample to the test amplifier. In the other extreme, a passive unswitched network of combiners combines all of the sampled outputs into a single output that is fed to the test amplifier. The amplified signal is transmitted from a wide angle transmit antenna to the single ground test station. The wide angle transmit antenna allows transmission of the downlink signal regardless of the position of the satellite. The test procedure is repeated for each receive antenna, with the received downlink signals being used to verify the operation of the satellite's repeater.
A disadvantage of previous methods of testing in-orbit satellites, is time and cost. Multiple downlink test sites are required to receive and analyze the multiple downlink signals. As the number of transmit antennas being fed by a receive antenna increased, so does the number of test sites required to verify operation. The new test method overcomes this disadvantage by providing a method of testing multiple receive antennas and their corresponding transponders from a single ground test station.
Another advantage of the new method of testing an inorbit satellite is its use of existing satellite hardware. The only additional hardware required are directional couplers for sampling the downlink signals, a matrix of signal combiners and/or switches to provide a single combined downlink test signal, and a wide angle coverage transmit antenna.
These and further features and advantages of the invention will be apparent to those skilled in the art from the following detained description, taken together with the accompanying drawings, which are not to scale.
REFERENCES:
Kasstan, Bernard, “In-Orbit Testing of Communications Satellites: An Introduction”,International Journal of Satellite Communications, Sep.-Oct. 1995, vol. 13, No. 5.
Egly et al., “In-Orbit Test of the First Hughes United States Direct Broadcast Satellite”,International Journal of Satellite Communications, Sep.-Oct. 1995, vol. 13, No. 5, 301-312.
Kasstan, et al., Recent Advances in “In-Orbit Testing of Communications Satellites”,International Journal of Satellite Communications, Sep.-Oct. 1995, vol. 13, No. 5, 377-401.
Moens, et al., ESA's In-orbit Test Facilities for Communications Satellites,International Journal of Satellite Communications, Sep.-Oct. 1995, vol. 13, No. 5, 403-412.
Koppel & Jacobs
Perez-Gutierrez Rafael
The Boeing Company
Trost William G.
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