HIGH ACCURACY DIRECTION FINDING SYSTEM

• US 3,824,595 A
• Filed: 06/04/1971
• Issued: 07/16/1974
• Est. Priority Date: 06/04/1971
• Status: Expired due to Term

• Current Assignee: AIL Systems, Inc. (ITT, Inc.)
• Original Assignee: Stanley Rylon Hall
• Inventors: Hall, Stanley Rylon
• Primary Examiner(s): Tubbesing, T. H.
• Assistant Examiner(s): Blum, T. M.
• Application Number:
  US05/149,949
• Time in Patent Office: 1,138 Days
• Field of Search: 343/113R,119R,16R,1CL,114R
• US Class Current: 342/432
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 3/143 by vectorial combination of signals derived from differently oriented antennae
• 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

Abstract

A method and apparatus for performing high accuracy direction finding. The amplitude difference and phase difference of a signal as received at a single pair of squinted antennas are determined. A fine but ambiguous indication of the direction is generated from the determined phase difference and a rough but unambiguous indication of direction is generated from the determined amplitude difference. The rough unambiguous indication is then utilized to resolve the ambiguity of the fine indication.

Claims

1. A system for determining the direction of arrival of an electrical signal within a field of view comprising:

a single pair of squinted antennas spaced by a distance greater than one-half wavelength for the maximum frequency of signal applied to the system;

means for determining the difference in amplitude and the difference in phase of said signal as received at said antennas;

means responsive to the determined phase difference for generating an ambiguous indication of said direction comprising two phase response signals;

means responsive to the determined amplitude difference for generating an unambiguous indication of said direction; and

means for utilizing the phase responsive signal of said unambiguous direction indication having the lowest absolute valve to resolve the ambiguity of said ambiguous indication.

2. A system for determining the direction of arrival of an electrical signal within a field of view comprising:

a single pair of squinted antennas spaced by a distance greater than one-half wavelength for the maximum frequency of signal applied to the system;

meas for determining the difference in amplitude and the difference in phase of said signal as received at said antennas;

means responsive to the determined phase difference for generating an ambiguous indication of said direction;

means responsive to the determined amplitude difference for generating an unambiguous indication of said direction; and

means for utilizing said unambiguous direction indication to resolve the ambiguity of said ambiguous indication;

said phase response determining means generating at least one multicycle phase response signal for signals applied to the system over the system field of view;

said ambiguous indication being a phase indication which may appear on more than one of said response cycles;

said ambiguity resolving means including means for determining the cycle of the phase response signal on which said indication appears.

3. A system of the type described in claim 2 wherein said ambiguity resolving means includes means for determining the multiple of 2 pi by which said ambiguous indicatioN differs from the unambiguous indication, and means for adding said ambiguous indication to, or subtracting said ambiguous indication from, the determined multiple of 2 pi .

4. A system of the type described in claim 2 wherein there are two phase response signals, one a sine wave and the other a cosine wave;

wherein only the phase response signal having the lowest absolute value is utilized by said ambiguous indication generating means; and

wherein said ambiguous indication generating means includes means for generating the arcsin of the utilized phase response signal, and means responsive to the phase response signal utilized and whether the phase response signal is positive or negative for determining the octant of the generated arcsin value in a cycle of the waveform.

5. A system of the type described in claim 3 wherein said ambiguity resolving means includes means for selecting the multiple (N) of 2 pi to be utilized, said means including means for forming the effective difference ( Delta phi ) in pi radians between unambiguous phase related to said unambiguous indication and ambiguous phase related to said ambiguous indication, and logic means for selecting N in accordance with the following relationship:

2N-1<

Delta phi <

2N+1 .

6. A system of the type described in claim 3 wherein said ambiguous indication is a phase value which may be positive or negative;

and including means responsive to the sign of said phase value for determining whether said phase value is to be added or subtracted from the determined multiple of 2 pi .

7. A system of the type described in claim 2 wherein said unamibiguous indication generating means includes means responsive to said determined amplitude difference for generating an indication of one of M regions within said field of view;

and wherein said ambiguity resolving means includes means for adding or subtracting said ambiguous indication from at least part of said region indication to obtain an indication of said direction.

8. A system of the type described in claim 2 wherein said direction is given as an angle relative to system boresight;

including means for determing the sign of the determined amplitude difference; and

means responsive to said determined sign for indicating the side of boresight for said direction of arrival.

9. A system of the type described in claim 2 wherein said amplitude difference determining means includes means for obtaining the logarithm of the amplitude response of each of said antennas, and means for generating the difference of said logarithm, whereby the logarithm of the ratio of said amplitude responses is obtained.

10. A system of the type described in claim 2 wherein said phase difference determining means includes means for limiting the signals from said antennas to remove amplitude effects, and means for phase detecting the limited antenna outputs, the response of said phase detecting means being cos phi , where phi is the phase difference between the signals from the antennas.

11. A system of the type described in claim 10 wherein said phase difference determining means includes means for delaying the phase of one of the limited antenna outputs by 90*, and means for phase detecting the delayed limited output with the other limited output, the output from said phase detecting means being equal to -sin phi .

12. A system for determining the direction of arrival of an electrical signal within a field of view comprising:

a single pair of squinted antennas;

means for determining the difference in amplitude and the difference in phase of said signal as received at said antennas;

means responsive to the determined phase difference for generating an ambiguous indication of said direction;

means responsive to the determined amplitude difference for generating an unambiguous indication of said direction; and

means for utilizing said unambiguous directioN indication to resolve the ambiguity of said ambiguous indication;

said phase difference determining means including a 90* hybrid and a 180* hybrid, the signals from both of said antennas being applied to both of said hybrids, and means for generating the log of the ratio of the responses from each of said hybrids.

13. A system for determining the angle of arrival of an electrical signal within a field of view comprising:

means for generating two separate multi-cycle phase response signals for input signals applied to said system over its field of view and also including means for selecting the phase response signal generated for a given signal which has the lowest absolute value, there thus being an ambiguity as to the correct response cycle for the response signals generated for a given input signal;

means for generating an amplitude response ratio for a signal applied to said system, said means generating a linear response ratio for input signals applied to said system over its field of view; and

means for utilizing said amplitude response ratio to resolve the ambiguity of said phase response ratio.

14. A system of the type described in claim 13 wherein a single pair of squinted antennas are utilized by both said phase and amplitude response generating means.

15. A system of the type described in claim 14 wherein each of said antennas has an amplitude response;

and wherein said amplitude response ratio is a logarithmic function of said amplitude responses.

16. A system of the type described in claim 13 wherein said angle is relative to system boresight;

including means for determining the sign of a generated amplitude response ratio; and

means responsive to said determined sign for indicating the side of boresight for said angle of arrival.

17. A system for determining the angle of arrival of an electrical signal within a field of view comprising:

means for generating a phase response signal for a signal applied to said system, said means generating a multi-cycle response signal for input signals applied to said system over its field of view, there thus being an ambiguity as to the response cycle for the response ratio generated for a given input signal;

means for generating an amplitude response ratio for a signal applied to said system, said means generating a linear response ratio for input signals applied to said system over its field of view;

means for utilizing said amplitude response ratio to resolve the ambiguity of said phase response signal;

said ambiguity resolving means including means responsive to said amplitude response ratio for deriving a first value representing said angle;

means responsive to said phase response signal for deriving a second value representing said angle;

means for determining the multiple of 2 pi by which said first and second values differ; and

means for adding said second value to, or subtracting said second value from, the determined multiple of 2 pi .

18. A method for determining the direction of arrival of an electrical signal comprising the steps of:

determining the difference in amplitude and the difference in phase of said signal as received at a single pair of squinted antennas;

generating from said determined phase difference an ambiguous indication of said direction comprising two phase response signals;

selecting the phase response signal having the lowest absolute value generating from said determined amplitude difference an unambiguous indication of said direction; and

utilizing said unambiguous indication to resolve the ambiguity of said ambiguous indication.

19. A method for determining the direction of arrival of an electrical signal comprising the steps of:

determining the difference in amplitude and the difference in phase of said signal as received at a single pair of squinted antennas;

generating from said determined phase difference an ambiguous indication of saId direction;

generating from said determined amplitude difference an unambiguous indication of said direction;

utilizing said unambiguous indication to resolve the ambiguity of said ambiguous indication;

said first mentioned step of generating producing a phase response signal such that a plot of said phase response signal for signals applied to the system versus direction of arrival over the system field of view yields at least one multicycle waveform and wherein said ambiguous indication is a phase indication which may appear on more than one of said phase response cycles; and

said ambiguity resolving step including the step of determining the cycle of the phase response ratio on which said indication appears.

20. A method of the type described in claim 19 wherein said ambiguity resolving step includes the steps of determining the multiple of 2 pi by which said ambiguous indication differs from the unambiguous indication, and the step of adding said ambiguous indication to, or subtracting said indication from, the determined multiple of 2 pi .

21. A method of the type described in claim 19 wherein there are two phase response signals, one a sine wave and the other a cosine wave;

wherein only the phase response signal having the lowest absolute value is utilized during said ambiguous indication generating step; and

wherein said ambiguous indication generating step includes the steps of generating the arcsin of the utilized response signal, and determining the octant of the generated arcsin value in a cycle of the waveform from information relating to the response signal utilized and whether the response signal is positive or negative.

22. A method of the type described in claim 20 wherein said ambiguity resolving step includes the steps of selecting the multiple (N) of 2 pi to be utilized, said step including the step of forming the effective difference ( Delta phi ) in pi radians between unambiguous phase related to said unambiguous indication and ambiguous phase related to said ambiguous indication, and selecting N in accordance with the following relationship:

2N-1<

Delta phi <

2N+1 .

23. A method of the type described in claim 20 wherein said ambiguous indication is a phase value which may be positive or negative;

and including the step of determining whether said phase value is to be added or subtracted from the determined multiple of 2 pi in response to the sign of the phase value.

24. A method of the type described in claim 19 wherein said unambiguous indication generating step includes the step of utilizing determined amplitude difference for generating an indication of one of M regions within said field of view;

and wherein said ambiguity resolving step including the step of adding or subtracting said ambiguous indication from at least part of said region indication to obtain an indication of said direction.

25. A method of the type described in claim 19 wherein said direction is given as an angle relative to system boresight;

including the steps of determining the sign of the determined amplitude difference; and

utilizing said determined sign for indicating the side of boresight for the direction of arrival.

26. A method of the type described in claim 19 wherein said amplitude difference determining the step includes the steps of generating the logarithm of the amplitude response of each of said antennas, and generating the difference of said logarithms, whereby the logarithm of the ratio of said amplitude responses is obtained.

27. A method of the type described in claim 19 wherein said phase difference determining step includes the steps of limiting the signals from said antennas to remove amplitude effects, and phase detecting the limited antenna outputs, the response from said phase detecting step being cos phi , where phi is the phase difference between the signals from the antenna.

28. A method of the type descRibed in claim 23 wherein said phase difference determining step includes the steps of delaying the phase of one of the limited antenna outputs by 90*, and phase detecting the delayed limited output with the other limited output, the result of said phase detecting step being equal to -sin phi .

29. A method of the type described in claim 19 wherein said phase difference determining step includes the steps of applying the outputs from both antennas to a 90* hybrid, applying both antenna outputs to a 180* hybrid, and generating the log of the ratio of the responses from each of said hybrids.

30. A method of the type described in claim 29 wherein said ambiguity resolving step includes the steps of determining which of said hybrid response ratios has the lower absolute value, utilizing the hybrid response ratio determined above in conjunction with an unambiguous indication determined from said amplitude difference to generate an ambiguous indication of direction, adding multiples of 2 pi to said determined value, determining the sum of the above addition which gives an indication most nearly equal to the unambiguous indication, repeating the preceding three steps with the determined sum in place of the unambiguous value, and repeating the above four steps until the determined sum is the same as the value utilized in the first repeated step to generate the sum.

31. A method for determining the angle of arrival of an electrical signal within a field of view comprising the steps of:

generating two separate phase response signals for a signal applied to said system and selecting the phase response signal generated for a given signal which has the lowest absolute value each of said phase response signals having multiple cycles for input signals applied to said system over its field of view, there thus being an ambiguity as to the response cycle for the response signal generated for a given input signal;

generating an amplitude response ratio for a signal applied to said system, said ratio having a linear response for input signals applied to said system over its field of view; and

utilizing said amplitude response ratio to resolve the ambiguity of said phase response ratio.

32. A method of the type described in claim 31 wherein a single pair of squinted antennas are utilized to generate inputs for both said phase and amplitude response ratio generating steps.

33. A method for determining the angle of arrival of an electrical signal within a field of view comprising the steps of:

generating a phase response signal for a signal applied to said system, said signal having multiple cycles for input signals applied to said system over its field of view, there thus being an ambiguity as to the response cycle for the response signal generated for a given input signal;

generating an amplitude response ratio for a signal applied to said system, said ratio having a linear response for input signals applied to said system over its field of view; and

utilizing said amplitude response ratio to resolve the ambiguity of said phase response ratio;

said ambiguity resolving step including the steps of deriving a first value representing said angle in response to said amplitude response ratio, deriving a second value representing said angle in response to said phase response signal, determining the multiple of 2 pi by which said first and second values differ, and adding said second value to, or subtracting said second value from, the determined multiple of 2 pi .