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Radio wawe direction finding methods
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WPI MQP Group:
Daniel Guerin - ECE
Shane Jackson - Physics
Jonathan Kelly - CS/ECE
Phase Interferometry Direction
Finding
WPI Advisors:
Ted Clancy
Germano Iannacchione
George Heineman
Group 108 Staff:
Chris Strus
Lisa Basile
Kelly McPhail
li17727Text BoxThis work is sponsored by the Department of the Air Force under Air Force Contract #FA8721-10-C-0007. Opinions, interpretations, conclusions, and recommendations are those of the authors and not necessarily endorsed by the United States Government.
li17727Text BoxDISTRIBUTION STATEMENT A. Approved for public release. Distribution is unlimited.
Direction Finding - 2
Group 108 10/01/12
Project Goal
Create a passive Direction Finding system for an airborne platform capable of determining the Angle of Arrival (AoA) in the azimuth plane.
Display results in a real-time graphical interface
Overview
Specifications
2.5 accuracy
40 dB dynamic range
90 field of view
1 Hz update rate
100 MHz bandwidth IF signal
X Band Frequency (8-12 GHz)
Secondary Objectives
Track 3 beacons
180 field of view
Direction Finding - 3
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Planned System
Provided by Lincoln Laboratory Project Scope
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1. Phase Interferometry
2. MATLAB Model
3. Prototype System
4. Summary
Contents
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Passive Direction Finding
Method Complexity Size Accuracy
Time Difference of Arrival Medium
Amplitude Comparison Low
Phase Interferometry High
Interferometer Geometry
(Massa, OConnor, Silva, 2011)
Scope of this project
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Phase Interferometry
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Phase Ambiguities
Phase eclipsing causes ambiguous results due to antenna
spacing and wavelength
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Phase Ambiguities
Phase eclipsing causes ambiguous results due to antenna
spacing and wavelength
+2
-2
0
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Phase Ambiguities
Phase eclipsing causes ambiguous results due to antenna
spacing and wavelength
+4
+6
+2
-2
-4
-6
0
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Resolving Ambiguities
Utilize multiple antennas for disambiguation
Compute Phase difference from Antenna 1 to 2
Compute Phase difference from Antenna 1 to 3
Compare possible angle solutions for common angle value
Antenna Spacing selected based on RF input requirement to minimize ambiguities
=10cm
=21cm
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Resolving Ambiguities
Adding a third antenna provides unambiguous result
Possible angles from
antennas 1 and 2
Possible angles from
antennas 1 and 3
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Resolving Ambiguities
Adding a third antenna provides unambiguous result
Possible angles from
antennas 1 and 2
Possible angles from
antennas 1 and 3
Direction Finding - 13
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1. Phase Interferometry
2. MATLAB Model
3. Prototype System
4. Summary
Contents
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MATLAB Model
Used to develop and test the direction finding algorithm
Simulates every step of the physical system
Pulsed wave generation, frequency down-converting, sampling waves
All processing steps in the final system tested in model first
Provided Hardware Project Scope
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MATLAB Model
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MATLAB Results
True AoA (degrees)
P = -40dBfs F = 12GHz D = 1km
Absolute Angle Error
An
gle
Err
or
(de
gre
es) Incorrect Ambiguity
Angle
Incorrect Ambiguity
Angle
Measured Angle vs. Actual Angle
Worst Case Scenario
Ca
lcu
late
d A
oA
(d
eg
ree
s) -90
0
90
True AoA (degrees) 90 0
An
gle
Err
or(
de
gre
es
)
-90 0 90 -45 45 0
2.5
5
Primary AoA
Secondary AoA
Rare ambiguity errors can cause
erroneous calculations
Algorithm Performance
Mean Error 0.097
Mean Certainty 0.87
Ambiguity Error 1.08%
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MATLAB Results
Incorrect Ambiguity Angle
Algorithm Performance
Mean Error 0.097
Mean Certainty 0.87
Ambiguity Error 1.08%
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1. Phase Interferometry
2. MATLAB Model
3. Prototype System
4. Summary
Contents
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Prototype System
Provided by Lincoln Laboratory Project Scope
Third input channel not implemented due to hardware issues
Three antenna mode tested with MATLAB inputs
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Prototype Results
Strong agreement between verified model and C algorithm
Processing time within specification
Data transfer accounts for 99.7% of latency
GUI demonstrated with simulated and captured data
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Real-Time Display GUI
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Real-Time Display GUI
Disambiguated Emitter Indication
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Real-Time Display GUI
Ambiguous Emitter Indication
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Real-Time Display GUI
Detailed Emitter Information
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Real-Time Display GUI
Angle Statistics
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Real-Time Display GUI
Frequency Statistics
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Real-Time Display GUI
Angle Certainty
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Real-Time Display Demo
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1. Phase Interferometry
2. MATLAB Model
3. Prototype System
4. Summary
Contents
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Performance
Combine phase interferometry and amplitude comparison for two antenna solution
Move real-time processing to FPGA
Enhance tracking algorithm to reduce probability of false ambiguity selection
Testing
Test three channel operation with live data
Verify operation with antennas connected
Future Work
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Successfully met all primary requirements with simulated signals
Extended field of view to 85
Capable of identifying multiple emitters per batch
Three channel operation verified with simulated data
Two channel operation verified with live signal generator data
Conclusion
Direction Finding - 32
Group 108 10/01/12
Emily Anesta
Lisa Basile
Ted Clancy
Sarah Curry
George Heineman
Germano Iannacchione
Kelly McPhail
Christopher Strus
Acknowledgements
Direction Finding - 33
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Resolving Phase
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Finding Optimal Antenna Separation
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GUI Sample for Two Channel Inputs