Hybrid estimation DF algorithm

• US 9,057,776 B1
• Filed: 06/14/2012
• Issued: 06/16/2015
• Est. Priority Date: 06/14/2012
• Status: Active Grant

• Current Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Wernicke, Kent A.
• Primary Examiner(s): McGue, Frank J
• Application Number:
  US13/523,474
• Time in Patent Office: 1,097 Days
• Field of Search: 342/424
• US Class Current: 1/1
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• 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 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

A hybrid method and system is disclosed for determining a direction finding (DF) to a received radio frequency (RF) signal. The method employs a linear interferometer array to receive and measure electrical phase differences in a received RF signal. A closed form analysis of the phase differences produces a first integer solution to which the method adds a plurality of offset values to produce a corresponding plurality of offset integer solutions. The number of offset values is proportional to the length of the baseline of the antenna array. These offset integer solutions are evaluated based on their deviation from measured phase differences by the array. Of the first integer solution and the offset integer solutions, one solution is selected based on a minimum deviation from the measured phase differences. The selected solution is output to a higher level processor and further displayed to an operator as the correct DF solution.

Claims

1. A method for determining a direction finding (DF) to a received radio frequency (RF) signal, the method comprising:

receiving, via a linear interferometer array, an RF signal;

receiving, from said linear interferometer array, at least two differences in electrical phase of said RF signal between at least three antenna elements of said linear interferometer array;

determining, via a closed form algorithm, a first integer solution based on said at least two differences in electrical phase;

determining, a plurality of adjacent integer solutions based at least in part on said first integer solution, each of said plurality of adjacent integer solutions having in common at least one variable;

determining a plurality of extended phase solutions based on one of said plurality of adjacent integer solutions and said at least two differences in electrical phase;

scaling said plurality of extended phase solutions based on a frequency of said RF signal, said scaling resulting in a plurality of scaled solutions;

determining a plurality of deviations associated with each of said plurality of scaled solutions from at least one of said at least two differences in electrical phase;

determining a minimum deviation from said plurality of deviations associated with each of said plurality of scaled solutions;

selecting one of said plurality of scaled solutions with said minimum deviation as an output DE;

configuring and transmitting said output DF to an analysis and control processor; and

displaying said output DF to an operator on a display.

2. The method of claim 1, wherein said receiving, from said linear interferometer array, at least two differences in electrical phase further comprises receiving a first phase difference, receiving a second phase difference, and receiving a long baseline phase difference.

3. The method of claim 1, wherein said plurality of adjacent integer solutions are related to said first integer solution by a plurality of fixed integers, said plurality of fixed integers offset a fixed distance from said first integer solution.

4. The method of claim 3, wherein said plurality of fixed integers are independent of a frequency and an intercept angle of said received RF signal.

5. The method of claim 1, wherein determining a plurality of extended phase solutions is further based in part on said long baseline phase difference.

6. The method of claim 1, wherein said plurality of fixed integers are further related by input phase values.

7. The method of claim 1, wherein said determining said plurality of extended phase solutions based on one of said plurality of adjacent integer solutions and said at least two differences in electrical phase further comprises use of said long baseline extended phase measurement.

8. The method of claim 1, wherein said scaling said plurality of extended phase solutions based on a frequency of said RF signal further comprises scaling based on a wavelength frequency and said long baseline extended phase measurement.

9. The method of claim 1, wherein said determining a minimum deviation further comprises a root mean square analysis of a combined difference for each of said plurality of scaled solutions, said combined difference based on at least:

1) a DF1 difference between said first phase difference and a scaled solution first phase estimate, and

     2) a DF2 difference between said second phase difference and a scaled solution second phase estimate, and

     3) a DFn difference between at least one additional phase difference and at least one additional scaled solution phase estimate.

10. The method of claim 1, wherein selecting one of said plurality of scaled solutions with said minimum deviation as an output DF further comprises removing from consideration a scaled solution from said plurality of scaled solutions whose value is outside a range of plus 1.0 to minus 1.0.

11. A computer readable medium storing non-transitory computer readable program code embodied therein for determining a direction finding (DF) to a received radio frequency (RF) signal, the non-transitory computer readable code comprising instructions which, when executed by a processor, perform the steps of:

receiving, via a linear interferometer array, an RF signal;

receiving, from said linear interferometer array, at least two differences in electrical phase of said RF signal between at least three antenna elements of said linear interferometer array;

determining, via a closed form algorithm, a first integer solution based on said at least two differences in electrical phase;

determining, a plurality of adjacent integer solutions based at least in part on said first integer solution, each of said plurality of adjacent integer solutions having in common at least one variable;

determining a plurality of extended phase solutions based on one of said plurality of adjacent integer solutions and said at least two differences in electrical phase;

scaling said plurality of extended phase solutions based on a frequency of said RF signal, said scaling resulting in a plurality of scaled solutions;

determining a plurality of deviations associated with each of said plurality of scaled solutions from at least one of said at least two differences in electrical phase;

determining a minimum deviation from said plurality of deviations associated with each of said plurality of scaled solutions;

selecting one of said plurality of scaled solutions with said minimum deviation as an output DE;

configuring and transmitting said output DF to an analysis and control processor; and

displaying said output DF to an operator on a display.

12. The method of claim 11, wherein said receiving, from said linear interferometer array, at least two differences in electrical phase further comprises receiving a first phase difference, receiving a second phase difference, and receiving a long baseline phase difference.

13. The method of claim 11, wherein said plurality of adjacent integer solutions are related to said first integer solution by a plurality of fixed integers, said plurality of fixed integers offset a fixed distance from said first integer solution.

14. The method of claim 13, wherein said plurality of fixed integers are independent of a frequency and an intercept angle of said received RF signal.

15. The method of claim 11, wherein determining a plurality of extended phase solutions is further based in part on said long baseline phase difference.

16. The method of claim 11, wherein said plurality of fixed integers are further related by input phase values.

17. The method of claim 11, wherein said determining said plurality of extended phase solutions based on one of said plurality of adjacent integer solutions and said at least two differences in electrical phase further comprises use of said long baseline extended phase measurement.

18. The method of claim 11, wherein said scaling said plurality of extended phase solutions based on a frequency of said RF signal further comprises scaling based on a wavelength frequency and said long baseline extended phase measurement.

19. The method of claim 11, wherein said determining a minimum deviation further comprises a root mean square analysis of a combined difference for each of said plurality of scaled solutions, the combined difference based on 1) a DF1 difference between said first phase difference and a scaled solution first phase estimate, and 2) a DF2 difference between said second phase difference and a scaled solution second phase estimate, and 3) a DFn difference between at least one additional phase difference and at least one additional scaled solution phase estimate.

20. The method of claim 11, wherein selecting one of said plurality of scaled solutions with said minimum deviation as an output DF further comprises removing from consideration a scaled solution from said plurality of scaled solutions whose value is outside a range of plus 1.0 to minus 1.0.