(AOA/LBI) emitter ranging method and apparatus

• US 5,343,212 A
• Filed: 12/11/1992
• Issued: 08/30/1994
• Est. Priority Date: 12/11/1992
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Industries, Inc. (Northrop Grumman Corporation)
• Inventors: Drude, Jeffrey J., Rose, Conrad M.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US07/992,965
• Time in Patent Office: 627 Days
• Field of Search: 342/417, 342/423, 342/424, 342/458, 364/449
• US Class Current: 342/424
• CPC Class Codes: G01S 11/04 using angle measurements

Abstract

An Angle of Arrival/Long Baseline Interferometer (AOA/LBI) passive ranging apparatus and method for emitter range determination can use any convenient airframe location for the two-antenna uncalibrated LBI baseline. This baseline has a theoretically unlimited length and does not require a specific SBI/LBI baseline ratio. Only a single initial AOA is required. Range partitions are formed along the single AOA. The emitter is assumed to lie in any of N range bins and the corresponding DOA (direction of arrival) unit vectors computed. Each of these DOA unit vectors is then used to predict the LBI phase differential and the N resolved LBI phases each drive a location estimator. The location estimator (filter) with consistent output provide the emitter range. The LBI range from these filters is used for subsequent DOA generation and ambiguity resolution.

Claims

1. A method for determining an emitter range using a long baseline interferometer (LBI), comprising the steps of:

(i) determining a single angle of arrival (AOA) of an emitter signal with an AOA detection device and outputting an AOA signal;

(ii) generating a plurality of initial range partitions, each partition having an initial assumed emitter position along said angle of arrival, using said AOA signal output from said AOA detection device;

(iii) performing an initial prediction of phase change of said emitter signal between elements of said LBI based on said initial plurality of assumed emitter positions;

(iv) measuring sequential LBI phase changes with phase change circuitry, said circuitry receiving emitter signals from said elements of said LBI;

(v) differentially resolving each of said measured LBI phase changes with said predicted LBI phase changes and generating a plurality of resolved phase signals, thereby providing an azimuth for each of said partitions;

(vi) at each measured phase change, generating a signal representing an estimated emitter location for each of said assumed emitter positions;

(vii) predicting subsequent LBI phase changes for each said estimated emitter location using said estimated emitter location;

(viii) differentially resolving said measured LBI phase changes with said subsequent LBI phase changes, generating a new azimuth for each partition and repeating steps vi, vii and viii, until a predetermined range criterion is met; and

(ix) generating a signal indicating a best range estimate as the emitter location from the plurality of estimated emitter locations generated.

2. A method for determining an emitter range according to claim 1 wherein said AOA detection device determines said angle of arrival by at least one of an amplitude DF measurement, an SBI, and an azimuth hypothesis test.

3. A method for determining an emitter range according to claim 1 wherein the step of determining a best range estimate is based on statistical properties of each said estimated emitter location.

4. A method for determining an emitter range according to claim 1 wherein the step of generating said estimated emitter location utilizes an optimal estimator.

5. A method for determining an emitter range according to claim 4 wherein said optimal estimator is a Kalman filter implemented in any convenient coordinate system.

6. A method for determining an emitter range according to claim 1 further comprising the step of generating a direction of arrival (DOA) unit vector for each assumed emitter position based on said angle of arrival.

7. A method for determining an emitter range according to claim 1 wherein said initial range partitions satisfying the inequality:

##EQU15## where a=fixed DOA bias,

a=true emitter bearing,

v⊥

=velocity component perpendicular to emitter bearing,

Δ

t=update time between measurements,

Δ

a=bearing change during update time,

d=interferometer baseline length, and

r_t =true range,

all converge to the correct range estimate.

8. A method for determining the location of an emitter comprising the steps of:

generating a plurality of initial unit vectors representing a set of ambiguous possible emitter locations along a measured initial angle of arrival;

resolving LBI phase ambiguities using a predicted emitter location;

performing range estimates for each LBI measurement received;

assigning to each said possible emitter location a probability that it is the correct emitter location;

resolving phax ambiguity; and

choosing the correct emitter location with probability one.

9. A method for determining an emitter range using a long baseline interferometer (LBI), comprising the steps of:

determining an angle of arrival (AOA) of an emitter signal once;

generating a plurality of range partitions corresponding to a plurality of assumed emitter positions along said angle of arrival;

computing a plurality of predicted LBI phase changes for each assumed emitter position;

measuring LBI phase changes of said emitter signal;

differentially resolving each of said measured LBI phase changes with said predicted LBI phase changes;

generating a plurality of emitter location estimates using optimal estimators for each partition;

weighting a location estimate based on statistical properties of the optimal estimators; and

choosing a best estimate as the emitter location from the plurality of emitter locations generated.

10. A method for determining an emitter range using a long baseline interferometer (LBI), comprising the steps of:

determining an angle of arrival (AOA) of an emitter signal once;

generating a plurality of range partitions corresponding to a plurality of assumed emitter positions along said angle of arrival;

generating a plurality of predicted LBI phase changes for each assumed emitter position;

determining a sequence of LBI phase changes;

differentially resolving each of said determined LBI phase changes with said predicted LBI phase changes;

generating a plurality of emitter locations using optimal estimators for each partition;

weighting a location estimate based on statistical properties of the optimal estimators; and

choosing a best estimate as the emitter location from the plurality of emitter locations generated.

11. An apparatus for determining an emitter range, comprising:

a long baseline interferometer;

means for measuring an angle of arrival (AOA) only once;

means for converting RF energy from said emitter received by said long baseline interferometer and said measuring means to an intermediate frequency signal;

means for determining LBI phase change of said emitter signal at antenna elements of said LBI using said intermediate frequency signal;

means for generating a plurality of assumed emitter positions along said angle of arrival;

means for computing a plurality of predicted LBI phase changes for each assumed emitter position;

means for differentially resolving said LBI phase change with said predicted LBI phase changes;

means for generating a plurality of emitter locations using an optimal estimator algorithm; and

means for generating a range estimate based on said emitter locations generated.