Beam alignment system and method for an antenna

• US 6,417,803 B1
• Filed: 04/03/2001
• Issued: 07/09/2002
• Est. Priority Date: 04/03/2001
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: McLain, Christopher, de La Chapelle, Michael, Parkman, David S.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H.
• Application Number:
  US09/825,575
• Time in Patent Office: 462 Days
• Field of Search: 342/359, 342/354, 342/422-427
• US Class Current: 342/359
• CPC Class Codes: G01S 3/20 derived by sampling signal received by an antenna system having periodically-varied orientation of directivity characteristic
• CPC Class Codes: H01Q 1/1257 using the received signal strength
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons

Abstract

An apparatus and method for correcting antenna beam misalignment between a transmit antenna and a receive antenna on a mobile platform such as an aircraft. The beam alignment method makes use of sequential lobing to determine the pointing angles in azimuth and elevation of a receive beam received by the receive antenna. For the transmit antenna, sequential lobing is used for the transmit antenna beam transmitted to a transponded satellite and then to a ground station. The ground station performs received signal strength indicator (RSSI) measurements and transmits these measurements back to the aircraft 16 via the target satellite. From these measurements, the beam misalignment between the receive and transmit antenna beams, both in azimuth and elevation, can be determined and a correction applied to the transmit antenna. The beam alignment procedure of the present invention can be implemented without interfering with normal use of the transmit and receive antennas and further ensures that interference with satellites adjacent to the target satellite will not occur during return link transmissions from the aircraft to the ground station.

Claims

1. A method for correcting for beam misalignment of a transmit antenna relative to a receive antenna such that a beam from said transmit antenna can be more accurately directed at a target which said receive antenna is aimed at, said method comprising the steps of:

a) determining a direction relative to said target which said receive antenna should be pointed at for optimizing reception of signals from said target;

b) causing said transmit antenna to transmit signals to said target;

c) causing said target to receive said signals and to transmit information back to said receiver, said information being related to a parameter of each of said transmitted signals;

d) using said information and said direction of said receive antenna to determine an alignment error between said transmit and receive antennas relative to said target at which both are being pointed; and

e) using said alignment error to more accurately point said beam of said transmit antenna at said target.

2. The method of claim 1, wherein step b) further comprises the step of causing said target to transpond said signals to a base station.

3. The method of claim 1, wherein step a) comprises determining said direction of said receive antenna by using a sequential lobing process.

4. The method of claim 1, wherein step a) comprises determining said direction of pointing of said receive antenna through a process including beam dithering.

5. The method of claim 1, wherein step a) comprises determining said direction of pointing of said receive antenna through a process including conical scanning.

6. The method of claim 1, wherein step a) comprises determining said direction of pointing of said receive antenna through a process including monopulse tracking.

7. The method of claim 1, wherein the information transmitted in step c) comprises information relating to a signal strength of said signals received by said target.

8. The method of claim 1, wherein the information transmitted in step c) comprises information relating to a carrier-to-noise (C/N) ratio of said signals received by said target.

9. The method of claim 1, wherein the information transmitted in step c) comprises information relating to an energy per bit divided by a noise spectral density (Eb/No) of said signals received by said target.

10. A method for correcting for beam misalignment of a transmit antenna relative to a receive antenna, wherein said antennas are supported on a structure adjacent one another, and wherein said antennas communicate with a satellite having a communications system and require aiming at said satellite to optimize performance thereof, said method comprising the steps of:

a) determining a direction that said receive antenna needs to be pointed at to aim said receive antenna at said satellite;

b) using said determined direction from step a) to initially point said transmit antenna at said satellite;

c) transmitting signals to said satellite from said transmit antenna to determine a beam center of said transmit antenna relative to said satellite;

d) causing said communications system of said satellite to transmit information back to said receive antenna which is indicative of a direction in which said beam center of said transmit antenna is pointing;

e) comparing said direction that said receive antenna is pointed at with said direction at which said transmit antenna is pointed at to determine a misalignment between said antennas relative to said satellite at which said antennas are pointed; and

f) adjusting pointing of said transmit beam to eliminate said misalignment.

11. The method of claim 10, further comprising the steps of:

using said communication system of said satellite to relay said signals to a ground station; and

using said ground station to generate said information and transmitting said information back to said satellite.

12. The method of claim 10, wherein said information comprises a signal strength of said signal transmitted from said transmit antenna.

13. The method of claim 10, wherein said information comprises a signal-to-noise ratio (S/N) of said signal transmitted from said transmit antenna.

14. The method of claim 10, wherein said information comprises a carrier-to-noise ratio (C/N) of said signal transmitted from said transmit antenna.

15. The method of claim 10, wherein said information comprises an energy per bit divided by noise spectral density (Eb/No) value of said signal transmitted from said transmit antenna.

16. The method of claim 10, wherein sequential lobing is used for determining said direction that said receive antenna is to be pointed at.

17. The method of claim 10, wherein beam dithering is used for determining said direction that said receive antenna is to be pointed at.

18. The method of claim 10, wherein conical scanning is used for determining said direction that said receive antenna is to be pointed at.

19. The method of claim 10, wherein monopulse tracking is used for determining said direction that said receive antenna is to be pointed at.

20. The method of claim 10, wherein one of beam dithering, conical scanning and monopulse tracking is used for determining said direction that said transmit antenna is pointing.

21. The method of claim 10, wherein step d) comprises transmitting information indicative of the pointing angles in azimuth and elevation of a transmit antenna beam directed at said satellite.

22. A method for correcting misalignment between a transmit antenna and a receive antenna of a mobile platform, relative to a satellite at which said antennas are pointed, and wherein the antennas are carried on the mobile platform adjacent to one another, the method comprising the steps of:

pointing said transmit antenna at said satellite in accordance with pointing information previously used to point said receive antenna at said satellite;

transmitting signals to said satellite from said transmit antenna;

analyzing said signals and supplying feedback signals from said satellite to said receive antenna indicative of the position of a beam center of a beam transmitted from said transmit antenna; and

using said feedback signals to more accurately point said transmit antenna at said satellite.