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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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