Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-09-17
2004-04-13
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S354000
Reexamination Certificate
active
06720918
ABSTRACT:
BACKGROUND
I. FIELD OF INVENTION
This invention relates to satellite communications and more specifically to estimating the thermal distortion of antennas on said spacecraft in order to ultimately compensate for the thermal distortion resulting in improved communications.
II. PRIOR ART
The prior art senses distortion (thermal and other) on the antenna of a spacecraft and compensates for the distortion so as to keep the beam properly positioned, e.g., various systems sample the distortion in real time periodically and compensate for same accordingly (up to 64 times/sec.) Problems are encountered with prior art systems e.g., when there are cloudy configurations or rain, the ground beam energy fades or does not transmit effectively to the spacecraft. The failure to transmit or sense results in the inability to correct at all.
In general, it is conventional to sense distortion relating to thermal and other disturbances or perturbations on the antenna of a spacecraft in order to measure same and ultimately compensate for the distortion so as to keep the beam properly positioned. Typically this may be done by employing a system which is continuously operated to sample either in real time or periodically to determine the distortion and then correct same. However, although these estimations and corrections may result in acceptable-to-excellent results, problems occur when there are outages or the absence of reliable data due to cloudy conditions, rain or other atmospherics causing the ground beam energy to fade or to reduce transmission effectively and/or terminate said transmission to the spacecraft.
In U.S. Pat. No. 5,940,034 there is described a system and method for RF autotracking multiple antennas to compensate for disturbances experienced by the antennas. The system and method uses two control algorithms implemented in fast and slow controllers and sums the results for each antenna that is tracked. Combinations and permutations of prior art have been implemented to provide redundancy in order to eliminate outages.
The prior art does not appear to appreciate nor resolve the problem of outages with regard to autotrack applications, i.e., non-fixed antenna systems.
III. OBJECTS OF INVENTION
It is, therefore, an object of this invention to provide a novel antenna distortion estimation and compensation system which overcomes the deficiencies of the prior art.
Another object is to provide a novel thermal compensation system. Still another object is to reduce dependency on ground beams. Yet another object of the invention is to provide a system which overcomes the solution inaccuracies present in the prior art with regard to these outages.
It is a further object of this invention to provide an antenna distortion estimation system that is unique and provides for proper pointing when outages occur.
A further object of this invention is to employ one beacon in an antenna distortion estimation system to provide proper pointing.
IV. SUMMARY OF THE INVENTION
These and other objects of the instant invention are accomplished generally speaking by providing a thermal distortion estimation system for delivering thermal time varying distortion of various spacecraft antenna comprising:
A system for estimating the thermal time varying distortion of spacecraft antenna is provided comprising a measurement signal outage indicator and a storage device which contains time varying distortion data.
The system of the instant invention generates a signal that determines an outage for the system received by the spacecraft and employs a generated time varying distortion of the system from a previous measurement history to predict the error resulting from the thermal distortion.
Any suitable method to determine signal outage for the system may be employed in the system of the instant invention. Typical sensors include a tracking receiver that measures the output of the automatic gain control loop.
Typical outage sensors would include those that measure the magnitude of the signal, and determine the position error to detect an outage. In other words, however the error position is sensed, it may also be used with appropriate processing to determine the presence of an outage.
In the general case, the thermal distortion estimation system of the instant invention would include an indicator which detects signal outage and a storage device which contains time varying distortion data. In a preferable embodiment of the instant invention the system may be mathematically defined or expressed as a Fourier Series from which the constants are determined by empirical data and optimally from historical thermal distortion data with a concentration of the data most closely corresponding in time to the outage.
REFERENCES:
patent: 5852792 (1998-12-01), Nielson
patent: 6320538 (2001-11-01), Lalezari et al.
Acosta, R.J. et al, “System Overview on Electromagnetic Compensation for Reflector Antenna Surface Distortion,” Digest Antennas and Propagation Society International Symposium, Jul. 1993, pp. 258-261.*
Rahmat-Samii, Y. “Reflector Antenna Distortion Compensation by Array Feeds: An Experimental Verification,” Electronic Letters, vol. 24, No. 18, Sep. 1988, pp. 1188-1190.*
Kim, David Y. et al, “Thermal Distortion Analysis on ACTS Multibeam Antenna,” Digest Antennas and Propagation Society International Symposium, Jun. 1988, pp. 1310-1313, vol. 3.
McGovern Lawrence
Reckdahl Keith
Issing Gregory C.
Karambelas & Associates
Space Systems Loral, Inc.
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