Beam waveguide antenna with independently steerable antenna beams and method of compensating for planetary aberration in antenna beam tracking of spacecraft

• US 6,225,961 B1
• Filed: 07/27/1999
• Issued: 05/01/2001
• Est. Priority Date: 07/27/1999
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: PRC, Inc. (Arthur D. Little, Inc.)
• Inventors: Benjauthrit, Boonsieng
• Primary Examiner(s): Wimer, Michael C.
• Assistant Examiner(s): Alemu, Ephrem
• Application Number:
  US09/361,355
• Time in Patent Office: 644 Days
• Field of Search: 455/13.3, 455/562, 455/12.1, 343/781 CA, 343/839, 343/840, 343/757, 343/758, 343/761, 342/350, 342/352, 342/354, 342/357, 342/358, 342/359
• US Class Current: 343/839
• CPC Class Codes: H01Q 1/125 Means for positioning
• CPC Class Codes: H01Q 19/19 comprising one main concave reflecting surface associated with an auxiliary reflecting surface
• CPC Class Codes: H01Q 19/191 wherein the primary active element uses one or more deflecting surfaces, e.g. beam waveguide feeds
• CPC Class Codes: H01Q 3/08 for varying two co-ordinates of the orientation

Abstract

An antenna assembly for forming and directing a transmit beam, and for controlling receive and transmit beam tracking of a spacecraft in the presence of planetary aberration. The assembly includes a main reflector, a sub-reflector centered along an optical axis of the main reflector, and a moveable transmit feed for directing electromagnetic radiation along a longitudinal axis thereof. The assembly also includes an intermediate beam waveguide assembly arranged between the moveable transmit feed and the main reflector, wherein the intermediate beam waveguide assembly includes fixed and moveable optical components for guiding electromagnetic beam energy between the moveable transmit feed and the main reflector. A beam steering mechanism is coupled with the moveable transmit feed for angularly displacing the transmit beam from the optical axis by displacing the moveable transmit feed in a direction substantially orthogonal to the longitudinal axis of the transmit feed.

Claims

1. A method of controlling a terrestrial antenna system to compensate for planetary aberration, comprising:

aligning a receive beam of the antenna system at a present time with a past position of a spacecraft; and

aligning a transmit beam of the antenna system with a future position of the spacecraft spaced from the past position, wherein a down-link signal and an uplink signal can be simultaneously received from the past position of the spacecraft and transmitted to the future position of the spacecraft by the antenna system, respectively.

2. The method of claim 1, wherein

the down-link and uplink signals travel round-trip between the spacecraft and the antenna system in a round-trip light travel time (RTLT),

the past position of the spacecraft coincides with a past time half a RTLT before the present time,

the future position coincides with a future time half a RTLT after the present time, and

an angular displacement between the receive and transmit beams is caused by planetary aberration.

3. The method of claim 2, further including the steps of

aligning the receive beam with the past position of the spacecraft by rotating an optical axis of the antenna system, and

angularly displacing the transmit beam from the receive beam by an amount equal to said angular displacement to align the transmit beam with the future position.

4. The method of claim 3, wherein said step of angularly displacing includes the step of displacing in a planar direction the transmit feed of the beam waveguide assembly from a positional origin of the transmit feed to cause said angular displacement of the transmit beam.

5. The method of claim 4, wherein the step of displacing in a planar direction includes the step of displacing the transmit feed in a planar direction with respect to a position of a fixed receive feed of the beam waveguide assembly.

6. The method of claim 4, further including the preparatory step of deriving said angular displacement between said receive and transmit beams using apriori spacecraft position information including predictions of the past and future positions and predicted times associated therewith.

7. The method of claim 6, further including the preparatory step of deriving said planar displacement of said transmit feeds responsive to said step of deriving said angular displacement.

8. The method of claim 7, wherein said step of deriving a planar displacement includes the step of deriving said planar displacement in planar polar coordinates.

9. The method of claim 8, further including the step of translating said planar polar coordinates to planar orthogonal coordinates.

10. The method of claim 8, further including the steps of generating at least one actuator control signal indicative of said planar displacement and supplying the actuator control signal to an input of an actuator coupled with the moveable transmit feed for imparting said planar displacement to said moveable transit feed.

11. The method of claim 10, wherein said step of generating at least one actuator control signal includes the step of generating first and second actuator control signals indicative of respective first and second orthogonal displacements of said moveable transmit feed.

12. The method of claim 1 including the step of continuously aligning the receive and transmit beams respectively with successive pairs of the past and future positions as the spacecraft follows the spacecraft trajectory.

13. A method of compensating for planetary aberration in an antenna system, said antenna system including a beam waveguide and a transmit feed for forming and directing a transmit beam, the transmit beam being adapted to transfer a signal between said transmit feed and a spacecraft, comprising:

angularly displacing the transmit beam from an optical axis of the beam waveguide responsive to a displacement of the transmit feed in a direction orthogonal to an axis of the transmit feed, to align the transmit beam with a future position of the spacecraft, the spacecraft moving from a present position to the future position during the approximate time taken for the transfer of the signal between the antenna system and the spacecraft.

14. An antenna system controller for a terrestrial antenna, the terrestrial antenna being adapted to form and direct transmit and receive beams for respectively transmitting a signal to and receiving a signal from a spacecraft, comprising:

a processor;

an interface coupled to said processor; and

a memory coupled to said processor, said memory having stored therein sequences of instructions which, when executed by said processor, causes said processor to;

identify temporally spaced first and second apriori positions of the spacecraft corresponding to a round-trip travel time of the signals between the spacecraft and the terrestrial antenna; and

derive an angular displacement between the receive and transmit beams to contemporaneously align the receive and transmit beams with spacecraft positions.