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Beacon Locator-1
Group 108
10/12/2011
The Beacon Locator Project
A Passive Direction Finding System for Locating Pulsed Emitter Signals
Presented By:
Christopher Massa
Erik Silva
Samantha O’Connor
October 12, 2011
Group 108 Staff:
-Chris Strus
-Scott Bailie
-Lisa Basile
WPI Advisors:
-Ted Clancy
-Germano Iannacchione
This work is sponsored by the Department of the Air Force under Air Force Contract #FA8721-05-C-0002.
Opinions, interpretations, conclusions, and recommendations are those of the author and not necessarily endorsed by the United States Government.
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Beacon Locator-2
Group 108
10/12/2011
Outline
• Project Overview
• Modeling
• Hardware Design
• Summary
Beacon Locator-3
Group 108
10/12/2011
• Passively locate direction of pulsed emitter signals
Objectives
• Analyze 3 methods of passive direction finding
– Time Difference of Arrival– Phase Difference– Amplitude Comparison
• Design hardware prototype using one direction finding method
Problem Statement and Project Objectives
θ
Beacon Locator-4
Group 108
10/12/2011
Project Specifications and Requirements
• ±2.5° accuracy
• 40 dB dynamic range
• 90° field of view
• Airborne system
• Real-time
• Restricted to azimuth plane
• Operate on 100 MHz bandwidth IF signal
Secondary
• Track 3 beacons simultaneously
Beacon Locator-5
Group 108
10/12/2011
Outline
• Project Overview
• Modeling
• Hardware Design
• Summary
Beacon Locator-6
Group 108
10/12/2011
Direction Finding Methods
Amplitude Phase &
Time Difference Of Arrival
Path length difference from sources to
separated antennas results in a phase
shift or TDOA between antennasIncoming signals cross the beam
pattern at different gain levels
= gain pattern
Beacon Locator-7
Group 108
10/12/2011
Time Difference of Arrival
a
b
c
d
Source Emitter
Receiver
Array
2m
6m
-40 -30 -20 -10 0 10 20 30 4010
-2
10-1
100
101
102Calculated Error Using TDOA with 250 MHz Sampling Frequency and Simulated Noise
Angle of Arrival (degrees)
Calculated Error (degrees)
5.1o
-5.1o
Signal Strength = 10 dBm
Noise Level = -50 dBm
SNR = 60 dB ..
= does not meet requirements
= meets requirements
Beacon Locator-8
Group 108
10/12/2011
Phase Comparison Direction Finding
• Calculate angle of arrival based on phase difference between signals at 2 antennas
• High accuracy but ambiguous solutions
R2 R1d
Tx
R2 R1d
θ
Beacon Locator-9
Group 108
10/12/2011
Phase Comparison Ambiguity
-40 -30 -20 -10 0 10 20 30 40
-40
-30
-20
-10
0
10
20
30
40
Possible Solutions Calculated Using Phase Comparison with Antennas Separated by 10 cm
Angle of Arrival (degrees)
Calculated Solution (degrees)
Beacon Locator-10
Group 108
10/12/2011
Phase Comparison Accuracy
-40 -30 -20 -10 0 10 20 30 4010
-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
Error in Calculation Using Phase Comparison with Antennas Separated by 10 cm and Simulated Noise
Angle of Arrival (degrees)
Calculated Error (degrees)
“Incorrect”
Ambiguous Solutions
Beacon Locator-11
Group 108
10/12/2011
Amplitude Comparison
-45° 45°
Angle of Arrival
x
x
An angle that is detected at each antenna will intersect
the antenna radiation beams at different gain values,
inducing different voltages at the antennas.
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2
x 10-5
0
0.5
1
1.5
2
2.5
3
3.5
Ratio of Voltage Magnitudes
Time (s)
Magnitude
Ratio of Magnitudes
Antenna 1 Magnitude in Volts
Antenna 2 Magnitude in Volts
Beacon Locator-12
Group 108
10/12/2011
Amplitude Comparison
-40 -30 -20 -10 0 10 20 30 400
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2Error Calculated Using Amplitude Comparison Method with 1.8-degree LUT Resolution and Simulated Noise
Angle of Arrival (degrees)
Calculated Error (degrees)
Beacon Locator-13
Group 108
10/12/2011
-40 -30 -20 -10 0 10 20 30 400
10
20
30
40
50
60
Angle of Arrival (degrees)
Dynamic Range (dB)
Angle of Arrival vs. Dynamic Range for ±±±±2.5o Accuracy
Amplitude Comparison Dynamic Range
40dB Spec.
Achievable Dynamic Range with ±2.5° of Accuracy
10 effective
ADC bits
Beacon Locator-14
Group 108
10/12/2011
Outline
• Project Overview
• Modeling
• Hardware Design
• Summary
Beacon Locator-15
Group 108
10/12/2011
Hardware
Hardware Direction Finding Device
• Amplitude comparison
• IF signal processor
• Implemented on FPGA
Desired System Specifications
• 100MHz bandwidth IF signals
• ±2.5° accuracy
• 40 dB dynamic range
• 90° azimuth extent
Beacon Locator-16
Group 108
10/12/2011
Signal Processing Platform
• Hardware– Innovative DSP X5 - 400M– Xilinx Virtex 5 SX95T– 2 x 14 bit ADC @ 250 MHz– 10 effective bits resolution
• Support Infrastructure– Existing PCI-Express
Control Hardware– PCIE Interface Program
Beacon Locator-17
Group 108
10/12/2011
Block Diagram
• Measure signal power for two antennas
• Calculate power ratio
• Determine angle of arrival
• Output to GUI
Signal
Emulator
ADC
Hilbert
Filters
PowerIndex
Search
Lookup
TableGUI
Hardware Data Processing
ADCPower
÷
Ethernet
Beacon Locator-18
Group 108
10/12/2011
Java Display
• Receives AOAs via TCP/IP
• Displays AOAs in graphical format
• 10 Hz refresh rate
Beacon Locator System
LAN Router
PC with Java Display
Host PC
FPGA
Beacon Locator-19
Group 108
10/12/2011
Testing and Results
• Input signals generated to test system over desired azimuth extent
• Most results meet ±2.5° accuracy
• Errors due to ADC bias and LUT clipping
Input Angle Calculated Angle Error
-44.6 -42.5 2.2
-40.5 -40.8 -0.4
-30.4 -31.0 -0.7
-20.3 -22.1 -1.8
-10.2 -10.2 -0.1
0.1 0.1 0.0
10.2 10.3 0.1
20.3 20.3 0.0
30.4 30.8 0.5
40.5 39.1 -1.4
44.6 40.7 -3.9
All values in degrees.
Full scale (+10dBm) input power
Beacon Locator-20
Group 108
10/12/2011
Outline
• Project Overview
• Modeling
• Hardware Design
• Summary
Beacon Locator-21
Group 108
10/12/2011
• Passively locate pulsed emitter signals
Summary
Specification Simulation Hardware
±2.5° accuracy ���� Between +40° and -45°
40 dB dynamic range Between +25° and -25° N/A
90° field of view ���� ����
Airborne system N/A ����
Real-time N/A ����
Azimuth plane ���� ����
100 MHz IF input ���� ����
Track 3 beacons ���� ����
Beacon Locator-22
Group 108
10/12/2011
Recommendations
Improve System Performance
• Higher quality ADC
Hybrid Amplitude/Phase System
• Resolve phase difference ambiguities
• Much higher accuracy
Multiple Emitter Tracking
• Currently handles single beacon
-40 -30 -20 -10 0 10 20 30 40
-40
-30
-20
-10
0
10
20
30
40
Elimination of Ambiguity through Combination of Amplitude and Phase Methods
Angle of Arrival (degrees)
Calculated Solution (degrees)
Beacon Locator-23
Group 108
10/12/2011
Acknowledgements
Chris Strus
Scott Bailie
Lisa Basile
Ted Clancy
Germano Iannacchione
Emily Anesta
David Hunter
Group 108
Beacon Locator-24
Group 108
10/12/2011
-45° 45°
-40 -30 -20 -10 0 10 20 30 40-8
-6
-4
-2
0
2
4
6
8
Angle of Arrival (degrees)
Difference in Gain, ∆∆ ∆∆G (dB)
Difference in Gain for Received Signals over 90o Azimuth Extent