Acquiring and tracking a satellite signal with a scanned antenna
A method and apparatus is disclosed herein for acquiring and tracking a satellite signal with an antenna. In one embodiment, the method comprises a) perturbing one or more of roll, pitch and yaw angles of an antenna orientation to create variant orientations associated with a first search pattern; b) computing new scan and polarization angles, in response to perturbed roll, pitch and yaw angles, for each of the variant orientations; c) receiving a radio-frequency (RF) signal from a satellite for each of the variant orientations; d) generating one or more receiver metrics representing a received RF signal associated with each of the variant orientations; e) selecting, as a new orientation, one of the variant orientations based on the one or more receiver metrics; and f) repeating a)-e) with the new orientation with a second search pattern narrower than the first search pattern.
1. A method for use with an electronically steered antenna having an inertial measurement unit (IMU) and an aperture of radio-frequency (RF) antenna elements configured to generate steered beams, the method comprising:
a) perturbing a value of one or more of roll, pitch and yaw angles of an antenna orientation produced with the IMU to create one or more variant orientations for which beam direction and polarization are calculated to create beams with the aperture to implement a first search pattern to search for a satellite during acquisition;
b) computing new scan and polarization angles, in response to perturbed roll, pitch and yaw angles, for each of the variant orientations;
c) receiving, using the aperture, a radio-frequency (RF) signal from the satellite for each of the variant orientations;
d) generating one or more receiver metrics representing a received RF signal associated with each of the variant orientations;
e) selecting, as a new orientation, one of the variant orientations based on the one or more receiver metrics;
f) repeating a)-e) with the new orientation and a second search pattern narrower than the first search pattern, the new orientation to be used to create additional variant orientations for which beam direction and polarization are calculated to create beams with the aperture to implement the second search pattern to search for the satellite during acquisition; and wherein f) is repeated until an observed satellite signal that meets predefined criteria is received.
2. The method defined in claim 1 wherein the second search pattern has a maximum angle that is decreased in comparison with that of the first search pattern.
3. The method defined in claim 1 wherein the antenna orientation is from a strap-down inertial navigation system (INS).
4. The method defined in claim 1 wherein the one or more signal metrics comprises Signal-to-Noise Ratio (SNR).
5. The method defined in claim 1 wherein the one or more signal metrics comprises Carrier-to-Noise Ratio (C/N).
6. The method defined in claim 1 wherein the RF signal from the satellite is received without physically moving an aperture of the antenna to steer the antenna.
7. The method defined in claim 1 wherein the first search pattern is a random pattern.
8. The method defined in claim 1 wherein the first search and second search patterns are a circular pattern.
9. The method defined in claim 1 wherein the first and second search patterns comprise noncontiguous points in the sky.
10. The method defined in claim 1 further comprising decreasing variance of the pattern after a good signal has been observed.
11. The method defined in claim 1 further comprising:
generating an offset based on the one or more receiver metrics; adding pointing corrections to the scan and polarization angles; and
applying scan and polarization angles with pointing corrections to an antenna.
12. The method defined in claim 11 wherein adding pointing corrections to the scan and polarization angles comprises:
adding receive pointing corrections to receive scan and polarization angles, and adding transmit pointing corrections to transmit scan and polarization angles; and
further wherein applying scan and polarization angles with pointing corrections to an antenna comprises:
applying the receive scan and polarization angles with pointing corrections to a receive portion of the antenna, and
applying the transmit scan and polarization angles with pointing corrections to a transmit portion of the antenna.
13. The method defined in claim 1 wherein perturbing one or more of roll, pitch and yaw angles of an antenna orientation to create variant orientations associated with a first search pattern comprises applying one or more attitude corrections to the roll, pitch and yaw angles of an antenna orientation based on the one or more receiver metrics.
14. The method defined in claim 13 wherein the one or more receiver metrics comprises Carrier-to-Noise Ratio (C/N).
15. An apparatus comprising:
an inertial measurement unit (IMU) configured to perturb a value of one or more of roll, pitch and yaw angles of an antenna orientation to create one or more variant orientations for which beam direction and polarization are calculated to create beams with the aperture to implement a first search pattern to search for a satellite during acquisition;
a computation unit coupled to the IMU and configured to compute new scan and polarization angles, in response to perturbed roll, pitch and yaw angles, for each of the variant orientations;
an electronically steered antenna coupled to the computation unit and responsive to the new scan and polarization angles, the antenna configured to receive an radio-frequency (RF) signal from a satellite for each of the variant orientations;
a modem coupled to the steerable antenna and the IMU and configured to generate one or more receiver metrics representing a received RF signal associated with each of the variant orientations, wherein the IMU is configured to select, as a new orientation, one of the variant orientations based on the one or more receiver metrics, the new orientation to be used to create a new set of variant orientations, by perturbing a value of one or more of roll, pitch and yaw angles of an antenna orientation, for which beam direction and polarization are calculated to create beams to implement a second search pattern that is narrower than the first search pattern to search for the satellite during acquisition,
wherein the IMU is configured to repeatedly generate sets of variant orientations until an observed satellite signal that meets predefined criteria is received by the antenna.
16. The apparatus defined in claim 15 wherein the second search pattern has a maximum angle that is decreased in comparison with that of the first search pattern.
17. The apparatus defined in claim 15 further comprising wherein the antenna orientation is from a strap-down inertial navigation system (INS).
18. The apparatus defined in claim 15 wherein the one or more signal metrics comprises Signal-to-Noise Ratio (SNR).
19. The apparatus defined in claim 15 wherein the one or more signal metrics comprises Carrier-to-Noise Ratio (C/N).
20. The apparatus defined in claim 15 wherein the RF signal from the satellite is received without physically moving an aperture of the antenna to steer the antenna.
21. The apparatus defined in claim 15 wherein the first search pattern is a random pattern.
22. The apparatus defined in claim 15 wherein the first search and second search patterns are a circular pattern.
23. The apparatus defined in claim 15 wherein the first and second search patterns comprise noncontiguous points in the sky.
24. The apparatus defined in claim 15 wherein the computation unit is configured to decrease comprising decreasing variance of the pattern after a good signal has been observed.