Method of detection and determining an angular location of frequency agile emitters
First Claim
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1. An apparatus for simultaneously associating frequency-agile transmitter signals detected by an intercept receiver with the frequency-agile transmitter, and measuring the signal'"'"'s angle-of-arrival (AOA), using phases measured between antenna pairs at diverse frequencies, comprising:
- a multiple baseline interferometer, a receiver pair associated with a single phase detector, an RF switch to connect the receiver-phase detector unit across the interferometer baselines to measure ambiguous phase, a frequency measurement device to measure signal frequency for each signal whose ambiguous phase is measured between interferometer antenna pairs, memory to store the phase, frequency and baseline length on which the phase was measured, selection logic for choosing a subset from the set of all measured ambiguous phases such that one phase measurement is selected for each interferometer baseline, phase ambiguity resolution logic for determining the integer, for each ambiguous phase measurement in this subset, such that when added to the ambiguous phase measurement this integer generates the resolved phase, correct to within the system measurement error, selection logic for choosing a single phase from the set of remaining ambiguous phase measurements, each made at frequencies distinct to within the resolution of the frequency measurement device, and appending this new phase to the set of previously chosen ambiguous phases, first iterative logic for repeating the steps of generating the ambiguity integers and resolving the phase ambiguities, comparing means for comparing the integers found by the iterative logic with the integers resolving the smaller set of ambiguous phase measurements made by the selection logic, memory for storing the new set of associated measured phases, the frequencies and interferometer baselines across which the phase measurements were made if the integer comparison is exact, or store the previous set of associated phases if the comparison is not exact, second iterative logic for appending a single new phase measurement to the associated set, resolving the phases of the enlarged set, and comparing the ambiguity integers found for the enlarged set with those found for the previous set, until all the frequency diverse measured phases have been compared by the comparing means, computation means for extracting the signal angle-of-arrival from the final set of resolved associated phases.
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Abstract
The present invention uses feedback 300 from RF carrier frequency measurements 301 to disassociate the emitter angle-of-arrival component 313 in the ambiguous phase measurement 312 from the initially unknown phase measurement integer ambiguities 314; to then process 302 resolve the ambiguities; and finally to process 303 to obtain the correct emitter AOA. The present invention does this by converting the actual interferometer baselines 315 on which the unassociated pulse 308 phase measurements 304 were made at different emitter frequencies to a baseline set 305 for a single-frequency equivalent interferometer array. This conceptual array has the following property: the phase measurement 306 that would be made on it at the fixed frequency for a signal at the same direction-of-arrival 307 are identical to the actual phase measurements made on the physical array. Because of this equivalency the conceptual array is called the E(equivalent)-array. But, whereas the physical array has antenna spacings 317 that are invariant, the E-array “antenna” spacings 316 change as a function of the RF carrier frequency measurement feedback 300, which depends on the particular residual pulses being tested. Thus there is a different E-array, even for the same frequency agile emitter, depending on the particular residual pulse set 309 used.
69 Citations
34 Claims
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1. An apparatus for simultaneously associating frequency-agile transmitter signals detected by an intercept receiver with the frequency-agile transmitter, and measuring the signal'"'"'s angle-of-arrival (AOA), using phases measured between antenna pairs at diverse frequencies, comprising:
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a multiple baseline interferometer, a receiver pair associated with a single phase detector, an RF switch to connect the receiver-phase detector unit across the interferometer baselines to measure ambiguous phase, a frequency measurement device to measure signal frequency for each signal whose ambiguous phase is measured between interferometer antenna pairs, memory to store the phase, frequency and baseline length on which the phase was measured, selection logic for choosing a subset from the set of all measured ambiguous phases such that one phase measurement is selected for each interferometer baseline, phase ambiguity resolution logic for determining the integer, for each ambiguous phase measurement in this subset, such that when added to the ambiguous phase measurement this integer generates the resolved phase, correct to within the system measurement error, selection logic for choosing a single phase from the set of remaining ambiguous phase measurements, each made at frequencies distinct to within the resolution of the frequency measurement device, and appending this new phase to the set of previously chosen ambiguous phases, first iterative logic for repeating the steps of generating the ambiguity integers and resolving the phase ambiguities, comparing means for comparing the integers found by the iterative logic with the integers resolving the smaller set of ambiguous phase measurements made by the selection logic, memory for storing the new set of associated measured phases, the frequencies and interferometer baselines across which the phase measurements were made if the integer comparison is exact, or store the previous set of associated phases if the comparison is not exact, second iterative logic for appending a single new phase measurement to the associated set, resolving the phases of the enlarged set, and comparing the ambiguity integers found for the enlarged set with those found for the previous set, until all the frequency diverse measured phases have been compared by the comparing means, computation means for extracting the signal angle-of-arrival from the final set of resolved associated phases. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
computation means to determine the signal angle-of-arrival from the resolved measured phases on all the equivalent baselines using a maximum likelihood estimator, logic to compare the emitter angle-of-arrival found from the associated-phase combined test-phase equivalent array, with the angle-of-arrival, or AOA, estimated from the associated phase set alone, and hence to further verify that the pulse sets having a unique ambiguity integer set intersection are from the same emitter by associating on the frequency agile emitter AOA.
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9. The apparatus of claim 3, wherein the determined integer set is added to the associated measured phases to resolve the measurement ambiguities and the emitter angle-of-arrival found using these resolved phase measurements, comprising:
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computation means to determine the signal angle-of-arrival from the resolved measured phases on all the equivalent baselines using a maximum likelihood estimator, logic to compare the emitter angle-of-arrival found from the associated-phase combined test-phase equivalent array, with the angle-of-arrival, or AOA, estimated from the associated phase set alone, and hence to further verify that the pulse sets having a unique ambiguity integer set intersection are from the same emitter by associating on the frequency agile emitter AOA.
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10. The apparatus of claim 4, wherein the determined integer set is added to the associated measured phases to resolve the measurement ambiguities and the emitter angle-of-arrival found using these resolved phase measurements, comprising:
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computation means to determine the signal angle-of-arrival from the resolved measured phases on all the equivalent baselines using a maximum likelihood estimator, logic to compare the emitter angle-of-arrival found from the associated-phase combined test-phase equivalent array, with the angle-of-arrival, or AOA, estimated from the associated phase set alone, and hence to further verify that the pulse sets having a unique ambiguity integer set intersection are from the same emitter by associating on the frequency agile emitter AOA.
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11. The apparatus claim 1, wherein the relation between baselines on which the phase measurements in the associated set were made, and the frequencies measured on the corresponding pulses, are given by
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1 φ 2 ⋮ φ n ] = 2 π c [ f 1 0 0 … … 0 0 f 2 … 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ 0 … … 0 0 0 … … 0 f n ] [ d → 1 d → 2 ⋮ d → n ] u → + 2 π n → + ɛ → φ and the baselines of the equivalent virtual array are given by
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12. The apparatus claim 3, wherein the relation between baselines on which the phase measurements in the associated set were made, and the frequencies measured on the corresponding pulses, are given by
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1 φ 2 ⋮ φ n ] = 2 π c [ f 1 0 0 … … 0 0 f 2 … 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ 0 … … 0 0 0 … … 0 f n ] [ d → 1 d → 2 ⋮ d → n ] u → + 2 π n → + ɛ → φ and the baselines of the equivalent virtual array are given by
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13. The apparatus claim 4, wherein the relation between baselines on which the phase measurements in the associated set were made, and the frequencies measured on the corresponding pulses, are given by
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1 φ 2 ⋮ φ n ] = 2 π c [ f 1 0 0 … … 0 0 f 2 … 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ 0 … … 0 0 0 … … 0 f n ] [ d → 1 d → 2 ⋮ d → n ] u → + 2 π n → + ɛ → φ and the baselines of the equivalent virtual array are given by
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14. The apparatus of claim 1, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by utilizing computation means to find the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, computation means to form the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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15. The apparatus claim 3, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by utilizing computation means to find the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, computation means to form the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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16. The apparatus claim 4, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by utilizing computation means to find the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, computation means to form the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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17. The apparatus claim 7, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by utilizing computation means to find the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, computation means to form the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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18. The apparatus of claim 14, wherein the set of E-array baselines is chosen to have the smallest number of ambiguities possible from the set of all feasible E-array baselines.
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19. The apparatus of claim 14 where a maximum likelihood estimator is used to determine the most likely correct set of possible integers from the projection of the phase measurements on the null space associated with the frequency-scaled baseline vector by minimizing the error N {right arrow over (φ
- )}−
N {right arrow over (m)}test over all the possible integer sets {right arrow over (m)}test.
- )}−
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20. The apparatus of claim 8 where the equivalent array baselines are chosen to include those having the greatest number of integer ambiguities in the clustered set, including resolving means to determine these ambiguities by predicting the integer values using the emitter angle-of-arrival found from the equivalent array set having the smallest number of integer ambiguities.
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21. A method for simultaneously associating frequency-agile transmitter signals detected by an intercept receiver with the frequency-agile transmitter, and measuring the signal'"'"'s AOA, using phases measured between antenna pairs at diverse frequencies, comprising:
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connecting a receiver-phase detector unit across interferometer baselines to measure ambiguous phase, measuring signal frequency for each signal whose ambiguous phase is measured between interferometer antenna pairs, storing the phase, frequency and baseline length on which the phase was measured, choosing a subset from the set of all measured ambiguous phases such that one phase measurement is selected for each interferometer baseline, determining the integer, for each ambiguous phase measurement in this subset, such that when added to the ambiguous phase measurement this integer generates the resolved phase, correct to within the system measurement error, choosing a single phase from the set of remaining ambiguous phase measurements, each made at frequencies distinct to within the resolution of the frequency measurement device, and appending this new phase to the set of previously chosen ambiguous phases, repeating the steps of generating the ambiguity integers and resolving the phase ambiguities, comparing the integers found by the iterative logic with the integers resolving the smaller set of ambiguous phase measurements made by the selection logic, storing the new set of associated measured phases, the frequencies and interferometer baselines across which the phase measurements were made if the integer comparison is exact, or store the previous set of associated phases if the comparison is not exact, appending a single new phase measurement to the associated set, resolving the phases of the enlarged set, and comparing the ambiguity integers found for the enlarged set with those found for the previous set until all the frequency diverse measured phases have been compared by the comparing step, and extracting the signal AOA from the final set of resolved associated phases. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
utilizing each measured frequency fi in conjunction with an arbitrary fixed fictitious frequency measurement fo to associate an equivalent virtual interferometer, this virtual interferometer having the property that its designed antenna spacings provide, for the same emitter signal angle-of-arrival, signal phase identical (within system measurement error) on the equivalent baseline at frequency fo to the signal phase measured at fi on the associated physical baseline, and utilizing fixed-frequency interferometer ambiguity resolution logic to find the integers resolving the phases measured on the equivalent interferometer baseline, and employs associative logic to assign these integer values to the corresponding phases on the physical array, and thereby resolve the diverse-frequency interferometer phase measurement ambiguities.
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23. The method of claim 22, comprising creating a new equivalent virtual array by combining the associated phase set with the test phase, and appending a new baseline to the previous virtual array baseline set, such that the new baseline length, at fictitious frequency fo, gives the same phase measurement as the ambiguous phase being tested and the comparing means compares the subset of integer phase ambiguities on the new virtual array with the corresponding integer phase ambiguity set on the associated phase equivalent array, and includes the test phase in the associated phase set if the comparison is exact.
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24. The method of claim 22, wherein the frequency measurement fo associated with the virtual interferometer is the average of the measured frequencies of all the phases used to form the equivalent virtual array.
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25. The method of claim 22, wherein the determined integer set is added to the associated measured phases to resolve the measurement ambiguities and the emitter AOA found using these resolved phase measurements, comprising:
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determining the signal AOA from the resolved measured phases on all the equivalent baselines using a maximum likelihood estimator, comparing the emitter AOA found from the associated-phase combined test-phase equivalent array, with the AOA estimated from the associated phase set alone, and hence to further verify that the pulse sets having a unique ambiguity integer set intersection are from the same emitter associating on the frequency agile emitter AOA.
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26. The method of claim 24, wherein the determined integer set is added to the associated measured phases to resolve the measurement ambiguities and the emitter AOA found using these resolved phase measurements, comprising:
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determining the signal AOA from the resolved measured phases on all the equivalent baselines using a maximum likelihood estimator, comparing the emitter AOA found from the associated-phase combined test-phase equivalent array, with the AOA estimated from the associated phase set alone, and hence to further verify that the pulse sets having a unique ambiguity integer set intersection are from the same emitter associating on the frequency agile emitter AOA.
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27. The method of claim 22, wherein the relation between baselines on which the phase measurements in the associated set were made, and the frequencies measured on the corresponding pulses, are given by
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1 φ 2 ⋮ φ n ] = 2 π c [ f 1 0 0 … … 0 0 f 2 … 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ 0 … … 0 0 0 … … 0 f n ] [ d → 1 d → 2 ⋮ d → n ] u → + 2 π n → + ɛ → φ and the baselines of the equivalent virtual array are given by
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28. The method of claim 24, wherein the relation between baselines on which the phase measurements in the associated set were made, and the frequencies measured on the corresponding pulses, are given by
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1 φ 2 ⋮ φ n ] = 2 π c [ f 1 0 0 … … 0 0 f 2 … 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ 0 … … 0 0 0 … … 0 f n ] [ d → 1 d → 2 ⋮ d → n ] u → + 2 π n → + ɛ → φ and the baselines of the equivalent virtual array are given by
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29. The method of claim 22, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by finding the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, forming the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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30. The method of claim 23, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by finding the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, forming the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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31. The method of claim 28, wherein the phase ambiguities are found by disassociating both the frequency and the AOA contributions to the phase measurements from the ambiguity integer part by finding the null space N of the frequency-scaled baseline vector
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= [ f 1 f o d → 1 f 2 f o d → 2 ⋮ f n f o d → n ] for each equivalent array set formed in the associated-phase test-phase comparison, forming the vector dot product of each basis vector in this null space with the vector of ambiguous phase measurements, computation means to form the vector dot product of all possible vectors of ambiguity integers with each basis vector in this null space set, logic to compare the two resulting number arrays N {right arrow over (φ
)} and N {right arrow over (m)}test of dot products and chose the particular N {right arrow over (m)}test closest to N {right arrow over (φ
)} thus determining {right arrow over (m)}test.
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32. The method of claim 31, wherein the set of E-array baselines is chosen to have the smallest number of ambiguities possible from the set of all feasible E-array baselines.
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33. The apparatus of claim 31, wherein a maximum likelihood estimator is used to determine the most likely correct set of possible integers from the projection of the phase measurements on the null space associated with the frequency-scaled baseline vector by minimizing the error N {right arrow over (φ
- )}−
N {right arrow over (m)}test over all the possible integer sets {right arrow over (m)}test.
- )}−
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34. The method of claim 25, wherein the equivalent array baselines are chosen to include those having the greatest number of integer ambiguities in the clustered set, including determining these ambiguities by predicting the integer values using the emitter AOA found from the equivalent array set having the smallest number of integer ambiguities.
Specification
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Current AssigneeNorthrop Grumman Systems Corporation (Northrop Grumman Corporation)
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Original AssigneeLitton Systems Incorporated
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InventorsRose, Conrad M.
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Primary Examiner(s)Phan, Dao
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Application NumberUS09/487,209Time in Patent Office657 DaysField of Search342/156, 342/424, 342/434, 342/442, 342/444, 342/445US Class Current342/424CPC Class CodesG01S 3/48 the waves arriving at the a...
