Detecting system having a coherent sparse aperture

• US 6,724,340 B1
• Filed: 02/13/2003
• Issued: 04/20/2004
• Est. Priority Date: 02/13/2003
• Status: Active Grant

• Current Assignee: Information Systems Laboratories, Inc.
• Original Assignee: Information Systems Laboratories, Inc.
• Inventors: Carlos, John Don, Bergin, Jameson, Kirk, David R., Techau, Paul M., Halsey, J. Doss
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Andrea, Brian K
• Application Number:
  US10/367,025
• Time in Patent Office: 432 Days
• Field of Search: 342/27, 342/59, 342/159, 342/126, 342/146, 342/149, 342/13, 342/16, 342/450, 342/463, 342/465
• US Class Current: 342/22
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: G01S 7/414 Discriminating targets with respect to background clutter

Abstract

A system and method for detecting a target object through foliage includes a transmitter for generating a low-frequency electromagnetic signal. The signal is directed toward a potential target object for reflection from the potential target object. The system further includes a plurality of mutually dispersed sensors for receiving the reflected signal from the target object. A mechanism is provided to determine the relative locations of the sensors. Signal information from the received signals is sent to a central processor. The central processor inputs the signal information into a beamformer algorithm such as the Maximum Likelihood Method (MLM) to reduce sidelobe ambiguities and resolve the true location of the target from the signal information.

Claims

1. A system for detecting a target object through foliage and determining the target object'"'"'s location, said system comprising:

a transmitter for generating an electromagnetic signal for reflection from said target object, said signal having a frequency less than approximately eight hundred megahertz (800 MHz);

a plurality of sensors for receiving said reflected signal from said target and generating signal information therefrom, said sensors being mutually dispersed at known locations;

a means for coherently processing said signal information and said sensor locations to generate a set of possible target locations, said set including sidelobe ambiguities and the actual location of said target;

at least one wireless link to send signal information from a said sensor to said processing means; and

a beamforming means for suppressing said sidelobe ambiguities to resolve said actual location from said set of possible target locations.

2. A system as recited in claim 1 wherein said beamforming means suppresses sidelobe ambiguities using a Maximum Likelihood Method (MLM) algorithm.

3. A system as recited in claim 1 further comprising a means for determining the relative positions of each said sensor.

4. A system as recited in claim 3 wherein said means for determining the relative positions of each said sensor comprises a plurality of global positioning satellite (GPS) locators with one said locator positioned at the location of each said sensor.

5. A system as recited in claim 3 wherein said means for determining the relative positions of each said receiver comprises a beacon transmitter.

6. A system as recited in claim 1 wherein each said sensor has one antenna element to receive said signal.

7. A system as recited in claim 1 wherein each said sensor has a plurality of antenna elements to receive said signal.

8. A system as recited in claim 1 wherein each said sensor is mounted on a different vehicle.

9. A system as recited in claim 8 further comprising a means for determining which sensors are stationary during signal receipt to allow signals received by non-stationary sensors to be eliminated from signal processing.

10. A system as recited in claim 1 wherein said signal has a frequency in the range of approximately thirty megahertz (30 MHz) to approximately eight hundred megahertz (800 MHz).

11. A system as recited in claim 1 wherein two said sensors define an angle, α

, with said target located at the vertex of said angle and wherein said two sensors are positioned relative to said target with said angle, α

, being between forty and sixty degrees.

12. A system for detecting a target object through foliage and determining the target object'"'"'s location, said system comprising:

a transmitter for generating an electromagnetic signal for reflection from said target object, said signal having a frequency less than approximately eight hundred megahertz (800 MHz) and a bandwidth less than approximately one hundred kilohertz (100 kHz);

a plurality of mutually dispersed sensors for receiving said reflected signal from said target and generating signal information therefrom;

a central processor for receiving said signal information from each said sensor and coherently processing said signal information to determine the location of said target object; and

at least one wireless link to send signal information from a said sensor to said central processor.

13. A system as recited in claim 12 wherein said central processor uses a Maximum Likelihood Method (MLM) beamforming algorithm to reduce sidelobe ambiguities and resolve the true location of said target object.

14. A system as recited in claim 12 wherein said system comprises a wireless link between said central processor and each said sensor to communicate said signal information from each said sensor to said central processor.

15. A method for determining a target object location, said method comprising the steps of:

transmitting an electromagnetic signal for reflection from said target object, said signal having a frequency less than approximately eight hundred megahertz (800 MHz);

receiving said reflected signal at a plurality of mutually dispersed locations and generating received signal information therefrom;

transmitting signal information from at least one sensor over a wireless link to a central processor; and

using said received signal information in a beamformer algorithm at said central processor to resolve the location of said target.

16. A method as recited in claim 15 wherein said signal is pulsed.

17. A method as recited in claim 15 wherein said signal information includes measurements of both received signal phase and received signal amplitude.

18. A method as recited in claim 15 wherein said beamformer algorithm is a Maximum Likelihood Method (MLM) algorithm.

19. A method as recited in claim 15 further comprising the step of determining the relative positions of each said receiving location.