Post on 06-Feb-2018
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
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
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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, O’Connor, Silva, 2011)
Scope of this project
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Phase Interferometry
θ
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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
+2π
-2π
0
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Phase Ambiguities
Phase eclipsing causes ambiguous results due to antenna
spacing and wavelength
+4π
+6π
+2π
-2π
-4π
-6π
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
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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
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Emily Anesta
Lisa Basile
Ted Clancy
Sarah Curry
George Heineman
Germano Iannacchione
Kelly McPhail
Christopher Strus
Acknowledgements
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Resolving Phase
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Finding Optimal Antenna Separation
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GUI Sample for Two Channel Inputs