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Precision rf antenna pointing

Precision rf antenna pointing description/claims

Embodiments of the present disclosure relate generally to Line-Of-Sight (LOS) pointing of spacecraft radio frequency (RF) antennas. More particularly, embodiments of the present disclosure relate to correction of LOS pointing errors of spacecraft RF antennas.

Precision pointing of an antenna LOS is used to accurately direct transmitting or receiving of an RF beam of an antenna to a receiving or transmitting antenna at a distance from the antenna. For spacecraft RF antennas, high precision is required because even small deviations from a correct LOS can result in a very large drop in signal power from transmitting antennas to receiving antennas. This is due to the fact that there is a large distance between spacecraft or ground antennas that transmit RF signals and ground or spacecraft antennas that receive the signals.

Many spacecraft RF communication and radar antennas require precision LOS pointing to meet mission objectives. Alignment, launch shift, deployment error and thermal deformation can all cause pointing errors. Alignment error is antenna miss-pointing error due to the fact that the LOS of an antenna is not aligned in the required direction. Launch shift error is antenna LOS shift caused by a rocket launch. Deployment error results from inaccuracy of a deployment mechanism. Thermal deformation error is caused by temperature change induced antenna structure deformation when the spacecraft is orbiting in its orbit. Alignment error, launch shift, and deployment error can be measured and corrected during spacecraft initial orbit calibration. Thermal antenna deformation, however, can not be completely calibrated and usually causes a significant amount of spacecraft antenna LOS pointing error during on-orbit operation.

A ground based beacon is often used to measure spacecraft RF antenna LOS pointing errors during operation on-orbit. These errors include the error caused by antenna structural thermal deformation. For commercial spacecraft, maintaining a ground based beacon for about 15-18 years is very expensive as equipment, facilities and human operation can easily cost customers millions of dollars. In many military applications, ground based beacons cannot be used because of their vulnerability to enemy attacks. Sometimes, in commercial applications, ground based beacons are unavailable in the antenna coverage area of the spacecraft.

A precision antenna pointing system and methods that measure and correct antenna structural deformation are disclosed. The system includes: an RF signal transmitting horn located a distance from an antenna reflector, which transmits an RF signal toward an antenna reflector, signal receiving horns attached to an edge of the antenna reflector, which receive the RF signal, an RF signal phase detector which is coupled to the signal receiving horn by receiving electronics and signal transportation harness, and is configured to estimate the phase of the RF signal received at each receiving horn; a LOS pointing estimator coupled to the signal processing electronics and phase detector, which estimates the precision RF antenna LOS pointing deviations using the phase estimates, and a stepping controller coupled to the antenna LOS pointing estimator, which corrects the RF antenna LOS pointing error based upon the estimates of the RF antenna LOS pointing deviations.

To achieve precision measurement and precision correction of antenna LOS pointing errors, the system uses a reference RF signal harness to compensate for signal phase variations in a signal transportation harness, and uses a multiplexer to multiplex RF signals from a transmitting horn and from each of the receiving horns with the same receiving electronics to minimize phase variations introduced by receiving electronics. The method uses phase differences between signals from the receiving horns and the signal from the transmitting horn, and phase differences between the signals from reference harness and the signal from transmitting horn to achieve a precision estimate of antenna LOS pointing.

According to an embodiment of the disclosure, the method first calibrates RF signal phase differences of the RF antenna LOS pointing control system at an initial calibration time to obtain reference signal phase differences. Then the method multiplexes measurement signals at measurement times, derives measurement signal phase differences based on the measurement signals, and computing signal phase changes between the reference signal phase differences and the measurement signal phase differences. Based on the signal phase changes, the method then estimates a precision phase deviation and generates an antenna LOS pointing estimate based on the precision phase deviation and computes an antenna actuator stepping command based on the antenna LOS pointing estimate. Next; the method corrects RF antenna LOS pointing based on the antenna actuator stepping command.

According to another embodiment of the disclosure, a further method continuously transmits a reference signal toward an antenna reflector to obtain a transmitting reference signal. The method then continuously receives the reference signal at reference signal receivers attached to an edge of the antenna reflector, and derives a phase estimate of the reference signal received at each of the reference signal receivers to obtain phase estimates. Then, the method computes estimates of precision RF antenna LOS pointing deviations using the phase estimates, and corrects the RF antenna LOS pointing error based upon the estimates of the precision RF antenna LOS pointing deviations.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

A more complete understanding of the embodiments of the present disclosure may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.

FIG. 1 is a schematic representation of the basic elements of a typical RF satellite antenna;

FIG. 2 is a diagram that illustrates an embodiment of a precision RF antenna LOS pointing control system that measures the RF antenna LOS pointing by detecting RF signal phases and that controls the RF antenna LOS by stepping the reflector of the RF antenna;

FIG. 3 is a table illustrating the ratio of an RF antenna LOS pointing determination error to an RF signal phase measurement error with respect to the size of an RF antenna reflector;

FIG. 4 is a diagram that illustrates an embodiment of a precision RF antenna LOS pointing control system that uses a reference harness to compensate for transporting harness and electronics induced phase variations; and

FIG. 5 is a flow chart that illustrates an RF antenna LOS pointing control process.

• Provisional Patent
• Utility Patent

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