Medium earth orbit satellite surveillance system and antenna configuration therefore

• US 20040113835A1
• Filed: 06/11/2003
• Published: 06/17/2004
• Est. Priority Date: 04/20/2000
• Status: Active Grant

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Jones, David A., Knight, James M., Jensen, Paul A., Jensen, Eric B., McCord, Henry L.
• Granted Patent: US 6,859,169 B2
• Time in Patent Office: Days
• US Class Current: 342/160
• CPC Class Codes: G01S 13/449 Combined with MTI or Doppler processing circuits
• CPC Class Codes: G01S 13/52 Discriminating between fixed and moving objects or between objects moving at different speeds
• CPC Class Codes: G01S 13/68 for angle tracking only
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 19/19 comprising one main concave reflecting surface associated with an auxiliary reflecting surface
• CPC Class Codes: H01Q 19/192 with dual offset reflectors
• CPC Class Codes: H01Q 25/00 Antennas or antenna systems providing at least two radiating patterns arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00

Abstract

A radar surveillance system includes a plurality of satellites a plurality of medium earth orbit satellites to provide continuous, long dwell coverage of a region of interest. Each satellite has an antenna having a main reflector and a subreflector electromagnetically coupled to the main reflector. A phased array generates multiple electromagnetic beams positioned so the electromagnetic beams reflect from the subreflector onto said main reflector. The system may be used in determining slow moving targets using a combination of monopulse anomaly and target spectral width measurements. The system also performs synthetic aperture radar imagery and focussed area fast moving target detection using alternating slope linear frequency modulated pulses. The plurality of medium Earth orbit satellites include a self-contained communications system consisting of high bandwidth self-relay crosslinks, high bandwidth downlink, and direct broadcast downlinks for processed data.

Claims

1. A surveillance system for observing locations on the earth comprising:

a plurality of medium earth orbit satellites, each satellite having an antenna having;

a main reflector having a first focal point;

a subreflector having a second focal point and electromagnetically coupled to said main reflector;

a phased array generating an electromagnetic beam positioned so the electromagnetic beam reflect from said subreflector so that some spillover occurs at a top portion of said main reflector.

2. A surveillance system as recited in claim 1 wherein each of said satellites comprises a high bandwidth crosslink for collected surveillance data, processed surveillance data, tracking, telemetry, and commands.

3. A surveillance system as recited in claim 1 wherein each of said satellites comprises a downlink for collected mission data.

4. A surveillance system as recited in claim 1 wherein each of said satellites comprises a crosslink and a downlink.

5. A surveillance system as recited in claim 1 wherein each antenna may generated multiple beams to said region of interest.

6. A system as recited in claim 1 wherein said satellites have moderate angles of inclination of about 30°

to 45°

according to the number of satellites in the constellation to provide continuous coverage of a surveillance region of interest.

7. A surveillance system as recited in claim 1 further comprising a moving target detection system consisting of a modified monopulse anomaly measurement augmented with a target spectral width measurement for slow moving targets

8. A surveillance system as recited in claim 1 further comprising a moving target detection system consisting of an alternating slope, linear frequency modulated transmitted pulses for fast moving targets

12. A surveillance system as recited in claim 1 wherein each of said satellites comprises active and passive remote sensing for radar moving target indication, synthetic aperture radar imagery, passive monitoring of electromagnetic spectrum, and radar illumination for cooperative airborne platform reception.

9. An antenna for a satellite comprising:

a main reflector having a first focal point;

a subreflector having a second focal point, and a electromagnetically coupled to said main reflector;

a phased array generating an electromagnetic beam positioned so the electromagnetic beam reflect from said subreflector so that some spillover occurs at a top portion of said main reflector.

10. An antenna as recited in claim 9 wherein said phased array is positioned downward and outward from a conjugate point.

11. A satellite comprising:

a satellite body;

a surveillance antenna coupled to said satellite body;

a bidirectional downlink/uplink antenna coupled to said satellite body;

a plurality of high bandwidth radio frequency or optical crosslinks coupled to said satellite body;

a high bandwidth downlink antenna coupled to said satellite body;

a medium bandwidth directed broadcast downlink coupled to said satellite body; and

,

a low bandwidth uplink receiver coupled to said satellite body.

13. A method for detecting moving targets comprising steps of:

establishing a discrete threshold;

obtaining a sum signal;

comparing the sum signal to the discrete threshold;

when the sum signal exceeds the discrete threshold, determining a monopulse anomaly;

when a monopulse anomaly is determined, classifying the signal as a stable mover;

when a monopulse anomaly is not found, statistically determining surrounding cells of an image to determine a power associated with interference or a discrete;

when the power ratio is low, the cells are classified as interference or a discrete;

when the power is high, classifying as an unstable mover.

14. A method as recited in claim 13 comprising the steps of:

removing discretes from the sum radar channel and the difference radar channel to form a modified sum radar channel and a modified difference radar channel;

recovering sum raw data and difference raw data from the modified sum radar channel and the difference radar channel;

determining cross-range velocities for the sum and difference raw data;

refocusing the raw data into sum and difference image data having discretes edited out and a number of cross-range velocities applied to the edited raw data;

estimating the antenna angles of stable and unstable moving targets;

reducing the probability of false alarm for stable targets using the monopulse anomaly effect.

15. A method as recited in claim 13 further determining the range and rate of all moving targets.

16. A method as recited in claim 13 further comprising the step of determining the cross-range velocity for moving targets using the cross-range focus value.

17. A method as recited in claim 13 further comprising the step of determining the antenna angle estimated by the final monopulse ratio.

18. A method as recited in claim 13 further comprising the step of measuring the characteristics of the spectra of unstable movers.

19. A method as recited in claim 13 wherein the step of refocusing enhances the detection of moving objects.