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.
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The Beacon Locator Project · Beacon Locator-3 Group 108 10/12/2011 • Passively locate direction of pulsed emitter signals Objectives • Analyze 3 methods of passive direction
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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