System and method for passively estimating angle and range of a source using signal samples collected simultaneously from a multi-aperture antenna

• US 20060279454A1
• Filed: 06/13/2005
• Published: 12/14/2006
• Est. Priority Date: 06/13/2005
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Schober, Michael B.
• Granted Patent: US 7,292,180 B2
• Time in Patent Office: Days
• US Class Current: 342/146
• CPC Class Codes: G01S 11/04 using angle measurements
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

A system and method for passively estimating range and angle of a source are disclosed. The source may be any wave source including radio-frequency (RF), optical, acoustic or seismic sources. In some RF embodiments, the system includes a single aperture antenna to simultaneously receive RF signals from the RF source through a plurality of sub-apertures, and a signal processor to perform a proximity test using samples simultaneously collected from the sub-apertures to determine whether or not to calculate angle and range estimates to the source based on either a curved wavefront assumption or a planar wavefront assumption.

Claims

1. A system for passively estimating range and angle of a source comprising:

an antenna to simultaneously receive signals from the source through a plurality of sub-apertures; and

a signal processor to perform a proximity test using samples simultaneously collected from the sub-apertures to determine whether or not to calculate angle and range estimates to the source based on either a curved wavefront assumption or a planar wavefront assumption.

2. The system of claim 1 wherein the signal processor further calculates both the angle and range estimates to the source using the simultaneously collected samples when the ratio exceeds a predetermined threshold.

3. The system of claim 2 wherein the proximity test performed by the signal processor comprises:

calculating a sum of mean-square-errors (MSEs) of the angle and range estimates to the source based on a curved wavefront equation using measured phases from each sub-aperture;

calculating a sum of the MSEs of the angle and range estimates to the source based on a planar wavefront equation using the measured phases from each sub-aperture; and

calculating a ratio of the sum of the MSEs calculated for the curved wavefront equation to the sum of the MSEs calculated for the planar wavefront equation.

4. The system of claim 3 wherein the signal processor calculates the angle and range estimates using a least-means-squared solution to a Fresnel approximation when the ratio exceeds a predetermined threshold.

5. The system of claim 2 wherein the signal processor measures a phase between initially collected samples of the simultaneously received signals generated from each of the sub-apertures.

6. The system of claim 2 wherein the signal processor calculates an angle estimate to the source when the ratio does not exceed the predetermined value using the simultaneously collected samples, and

wherein the signal processor refrains from calculating a range estimate to the source using the simultaneously collected samples when the ratio does not exceed the predetermined value.

7. The system of claim 2 wherein the antenna has an aperture comprising at least three sub-apertures,

wherein each sub-aperture comprises one or more array elements,

wherein a spacing between the elements and a location of the elements are used by the signal processor to calculate both the angle and range estimates to the source.

8. The system of claim 7 wherein the array elements are arranged in a linear fashion across the aperture and comprise a linear array of elements.

9. The system of claim 7 wherein the array elements are arranged in a linear fashion in both x and y directions of a surface of the aperture and comprise at least two linear arrays of elements.

10. The system of claim 7 wherein the array elements are arranged in a substantially arbitrary fashion on a surface of the aperture, the locations of the array elements being used by the signal processor to calculate the angle and range estimates.

11. The system of claim 2 further comprising a front-end circuitry having a plurality of receiver channels, each receiver channel to provide the simultaneously collected samples from an associated one of the sub-apertures.

12. The system of claim 1 wherein the source is a radio-frequency source.

13. The system of claim 1 wherein the source is an optical source.

14. The system of claim 1 wherein the source is an acoustic source.

15. A method of passively estimating angle and range to a signal source comprising:

simultaneously receiving signals from the source through a plurality of sub-apertures; and

performing a proximity test using samples simultaneously collected from the sub-apertures to determine whether or not to calculate angle and range estimates to the source based on either a curved wavefront assumption or a planar wavefront assumption.

16. The method of claim 15 further comprising calculating both the angle and range estimates to the source using the simultaneously collected samples when the ratio exceeds a predetermined threshold.

17. The method of claim 16 wherein the proximity test comprises:

calculating a sum of mean-square-errors (MSEs) of the angle and range estimates to the source based on a curved wavefront equation using measured phases from each sub-aperture;

calculating a sum of the MSEs of the angle and range estimates to the source based on a planar wavefront equation using the measured phases from each sub-aperture; and

calculating a ratio of the sum of the MSEs calculated for the curved wavefront equation to the sum of the MSEs calculated for the planar wavefront equation.

18. The method of claim 17 wherein calculating the angle and range estimates comprises calculating the angle and range estimates using a least-means-squared solution to a Fresnel approximation when the ratio exceeds a predetermined threshold.

19. The method of claim 16 further comprising measuring a phase between initially collected samples of the simultaneously received signals generated from each of the sub-apertures.

20. The method of claim 16 further comprising:

calculating an angle estimate to the source when the ratio does not exceed the predetermined value using the simultaneously collected samples; and

refraining from calculating a range estimate to the source using the simultaneously collected samples when the ratio does not exceed the predetermined value.

21. The method of claim 16 wherein the antenna has an aperture comprising at least three sub-apertures,

wherein each sub-aperture comprises one or more array elements,

wherein a spacing between the elements and a location of the elements are used to calculate both the angle and range estimates to the source.

22. The method of claim 21 wherein the array elements are arranged in a linear fashion across the aperture and comprise a linear array of elements.

23. The method of claim 21 wherein the array elements are arranged in a linear fashion in both x and y directions of a surface of the aperture and comprise at least two linear arrays of elements.

24. The method of claim 21 wherein the array elements are arranged in a substantially arbitrary fashion on a surface of the aperture, the locations of the array elements being used to calculate the angle and range estimates.

25. The method of claim 16 wherein receiving comprises receiving the simultaneously collected samples through plurality of receiver channels, each receiver channel to provide the simultaneously collected samples from an associated one of the sub-apertures.

26. The method of claim 15 wherein the source is a radio-frequency source.

27. The method of claim 15 wherein the source is an optical source.

28. The method of claim 15 wherein the source is an acoustic source.

29. A signal source locator comprising:

an antenna to simultaneously receive signals from the source through a plurality of sub-apertures; and

a signal processor to perform a proximity test using samples simultaneously collected from the sub-apertures to determine whether or not to calculate angle and range estimates to the source based on either a curved wavefront assumption or a planar wavefront assumption,

wherein the signal processor calculates both the angle and range estimates to the source using the simultaneously collected samples when the ratio exceeds a predetermined threshold, and

wherein the signal processor measures a phase between initially collected samples of the simultaneously received signals generated from each of the sub-apertures.

30. The signal source locator of claim 29 wherein the proximity test performed by the signal processor comprises:

calculating a sum of mean-square-errors (MSEs) of the angle and range estimates to the source based on a curved wavefront equation using measured phases from each sub-aperture;

calculating a sum of the MSEs of the angle and range estimates to the source based on a planar wavefront equation using the measured phases from each sub-aperture; and

calculating a ratio of the sum of the MSEs calculated for the curved wavefront equation to the sum of the MSEs calculated for the planar wavefront equation, and

wherein the signal processor calculates the angle and range estimates using a least-means-squared solution to a Fresnel approximation when the ratio exceeds a predetermined threshold.

31. The signal source locator of claim 30 wherein the signal processor calculates an angle estimate to the source when the ratio does not exceed the predetermined value using the simultaneously collected samples, and

wherein the signal processor refrains from calculating a range estimate to the source using the simultaneously collected samples when the ratio does not exceed the predetermined value.

32. The signal source locator of claim 29 wherein the source is a radio-frequency source.

33. The signal source locator of claim 29 wherein the source is an optical source.

34. The signal source locator of claim 29 wherein the source is an acoustic source.

35. A machine-accessible medium that provides instructions, which when accessed, cause a machine to perform operations comprising:

measuring a phase between initially collected samples of simultaneously received signals generated from each of a plurality of sub-apertures;

performing a proximity test using the initially collected samples of signals to determine whether or not to calculate angle and range estimates to the source based on either a curved wavefront assumption or a planar wavefront assumption; and

calculating both the angle and range estimates to the source using the simultaneously collected samples when the ratio exceeds a predetermined threshold.

36. The machine-accessible medium of claim 35 wherein the instructions, when further accessed cause the machine to perform operations,

wherein the proximity test comprises:

calculating a sum of mean-square-errors (MSEs) of the angle and range estimates to the source based on a curved wavefront equation using measured phases from each sub-aperture;

calculating a sum of the MSEs of the angle and range estimates to the source based on a planar wavefront equation using the measured phases from each sub-aperture; and

calculating a ratio of the sum of the MSEs calculated for the curved wavefront equation to the sum of the MSEs calculated for the planar wavefront equation,

wherein calculating the angle and range estimates comprises using a least-means-squared solution to a Fresnel approximation when the ratio exceeds a predetermined threshold.

37. The machine-accessible medium of claim 36 wherein the instructions, when further accessed cause the machine to perform operations comprising:

calculating an angle estimate to the source when the ratio does not exceed the predetermined value using the simultaneously collected samples; and

refraining from calculating a range estimate to the source using the simultaneously collected samples when the ratio does not exceed the predetermined value.

38. A system for passively estimating range and angle of a source comprising:

an antenna to receive signals from the source through a plurality of sub-apertures; and

a signal processor to calculate angle and range estimates to the source based on a curved wavefront assumption using a simultaneously collected single set of samples, wherein the signal processor calculates the angle and range estimates using a least-means-squared solution to a Fresnel approximation, and

wherein the antenna has an aperture comprising at least three sub-apertures, each sub-aperture comprising one or more array elements, wherein a spacing between the array elements and a location of the elements are used by the signal processor to calculate both the angle and range estimates to the source.