moving target emulators for ultra wide band signals .... 2008 rome ieee uwb modulation v3 - 2....

GTRI_B-12008 Rome IEEE UWB Modulation v3 - 1

Moving Target Emulators for Ultra Wide Band Signals: Electrically

Modulated Fragmented Surfaces

Dr. Rick L. Moore*, Mr. Paul Friederich,and Dr. Robert Rice*

Members and Senior Member, IEEE

Georgia Tech Research InstituteSignature Technology Lab

Georgia Institute of Technology400 10th. Street, 30332Atlanta Georgia, USA

(001) 404-407-6197, (001) 404-407-6195,: [email protected]


Outline• Goal: Design/Assemble a MTI Simulator for UWB Radar

testing• Measured data • Concept description and Status

• Approach: Electrical Modulation• Basis: Etched fragmented conducting panels• Design: Method of Moment (MoM) predictions; switches;

percolating surface calculated modulations• Measured Data

• Switch impedances• Surface modulations

• Conclusions and Additional Research


Goal: Achieve Doppler Simulation over Broad Frequency Sectors

Produce Asymmetric Side lobesApproach: Multi-area modulation of an Electrically Switched Panel

Symmetric sidelobes from amplitude modulation

Frequency reflected by a fixed target

Doppler shifted asymmetric sidelobes of approaching target

Am

plitu

de

FrequencyA

mpl

itude

Frequency


Example: MTI RADAR Audio Spectra

• A – tracked vehicle moving toward radar (steady speed);

• B – tracked vehicle reversing direction;

• C – tracked vehicle moving away from radar;

• D - wheeled vehicle moving away from radar and slowing down.

Target

C D

A B

Target

Target

Target

Target

Background


Concept: Complex WaveformSynthesis Concepts

H

E

Control Signals

Composite Backscatter

Incident EM Wave

Basic ScatteringDevice

CompositePanel

Stored Signal ROM

Fourier Transform

Inverse Fourier

TransformROM Look-

Up Table

f1

f2

f3

f4

A/Ds1

s2

sg

sN

A/DA/DA/D

Control Signal Output


UWB Target Simulator Status

• Wideband AM modulation achieved• Wideband complex signature emulations will require

control of reflectivity amplitude and phase• Related publications:

• A. Tennant, B. Chambers, Smart Mater. Struct. Vol. 13 (2004),pp 122-125.

• P. N. Kaleeba, A. Tenant and B. Chambers, “ Measured performance of active radar absorber with DC or modulated current control” Electronics Letters, Vol 41, no. 1, (2005),

• “Reflection of radar signals from multiple phase-modulated surfaces” ,IET Radar, Sonar & Navigation -- April 2007 --Volume 1, Issue 2, p. 142-148


0 5 10 15-25

-20

-15

-10

-5

0

"on""off"

0 5 10 15-25

-20

-15

-10

-5

0

"on""off"

Original Amplitude ModulationPanel Demonstration

• Conclusions• Needed wideband pattern approach• Requirement of measured switch impedances

Simulation forOne-inch Unit Cell Grid

Pow

er T

rans

mis

sion

(dB

)Frequency (GHz)


Etched Fragmented-Percolating Conducting Surfaces

Concept and Design Approach

• Percolating behavior with deterministic structures

• Example: 54% surface fraction

• On-off modulates "Backbone” and dominates low frequency response

• Short electrical lengths at high frequencies

• MoM simulations identified “critical” connections, along backbones, for switch placement

• Maximized bandwidth and modulation amplitude

• Investigated 4 unit cells and modified patterns

FETS, Diodes,

Polymers


Analysis Process and Photographof 1 inch Unit Cell Panel

• MoM code predicted R,T and I• Down selected for

performance below 10 GHz• Example optimized pattern

Photo

Measured-Calculated Currents (I)

Polarization

vertical horizontal


Example: Calculated Current Amplitude Locations vs. Relative Frequency

Tran

smis

sion

Relative Frequency


Switch Choices:FETS (Field Effect Transistor),

Diodes and Electrically Active Polymers

• FETS preferred: ease of integration during manufacture, bandwidth (low capacitance) and impedance variation

• Characterized FET impedances and applied data in panel designs

• FETS to be used in new panels and with polymers as long term candidates

• Chose diodes for demonstration panel due to cost and availability

Switch

• Use FDTD model and measured S11 an S12 to infer impedance

• Typical Open circuit values:FET 34143,C = 0.4494 Pf;R = 156879 ohm;L = 0.10719 nH

• Measurements differed from ideal predictions

Measured dipole S11 and S12

versus bias


Agilent FETS Measurements Compared to Idealized and Measured Impedance

Frequency (GHz)

0 1 2 3

S11

(dB

)

-30

-25

-20

-15

-10

-5

0

MeasurementsCCT Model

Frequency (GHz)

0 1 2 3

S11

(Deg

rees

)

-180

-90

0

90

180MeasurementsCCT Model

Impedance Corrected


Sample port tub0.1 1

-25

-20

-15

-10

-5

0

"off""on" Sample port tub

0.1 1-25

-20

-15

-10

-5

0

"off""on"

0.1 1-25

-20

-15

-10

-5

0


0.1 1-25

-20

-15

-10

-5

0


0.1 1-25

-20

-15

-10

-5

0

"off""on"

0.1 1-25

-20

-15

-10

-5

0

"off""on"

Unit Cell Size Increase Expands Modulation Bandwidth

MoM Predictions: Reflection (R), Transmission (T)

Sample port tube

Frequency (GHz)

0.01 0.1 1 10

Frequency (GHz)

0.01 0.1 1 10-25

-20

-15

-10

-5

0

“off”“on”

Sample port tube

Frequency (GHz)

0.01 0.1 1 10

Frequency (GHz)

0.01 0.1 1 10-25

-20

-15

-10

-5

0

“off”“on”

Frequency (GHz)

0.01 0.1 1 10

Frequency (GHz)

0.01 0.1 1 10-25

-20

-15

-10

-5

0

Frequency (GHz)

0.01 0.1 1 10

Frequency (GHz)

0.01 0.1 1 10-25

-20

-15

-10

-5

0

“off”“on”

RT

Fragmented Panel Expands Modulation Bandwidth

dB

dB

TTdB

R


Demonstration Panel Fabricationsand Measurements

• Panels etched on 18 inch square printed circuit board substrates.

• FETS not available for Test. Used surface mount PIN diodes with 0.35 pF junction capacitance

• 230 W at 2 GHz, 45 W at 10 GHz – limited bandwidth

• Demonstrate modulation at lower frequencies (i.e., larger unit cells)


Testing: Focused Beam System

Transmission; Reflection; Bistatic;

0-80 deg. Incidence; 2-18 GHz


Measured Response2 and 3-inch Unit Cell Panels

3-inch

2-inch


Example Data: Measured Transmissions at 3.905 GHz for Various Switching Waveforms

1 KHz triangle wave

No modulation 1 KHz sine wave

1 KHz square wave


Modulated Transmission (3.725 GHz) and Reflection at (2.6 GHz; 45° Bistatic)

• 1 KHz square wave modulation

• Frequency chosen for large phase change

• Symmetric sidelobes remain dominate


• 45 degree bistatic angle

• First sidelobe continues to be apparent at ~13 dB


Summary, Conclusions and Announcement

• Switched-diode panels can provide effective simple decoys

• Percolating patterns increase frequency coverage while minimizing control circuitry

• Single sideband decoy requires more sophisticated modulation/scatterer

• Further investigation merited: FET panels, control techniques and new panel designs and materials

• Continued research: Soliciting interest from student, Postdocs and visiting professors for UWBTech CoE (website)


Concepts for ConsiderationModulation surface concept

based on D. Sievenpiper Thesis(1999 Univ. of California)

Transmission change:FETS and resistive materials

Predicted Reflection for various polymer impedance values


End


Fragmented Panel Expands Modulation Bandwidth (1 inch Unit cells)


Additional Bandwidth Predicted with for Three-inch Unit Cell


Focused Beam Profile

Surfaces of Constant Phase

w0

Focusing LensBeamwaist

(Plane wave illumination)


Swept Frequency, Static Switch State


CW, Modulated Switches


Measured Response - 3-inch Unit Cell

Reflected Signal

Frequency (GHz)2 3 4 5 6 7 8

Transmitted Signal

Frequency (GHz)2 3 4 5 6 7 8

Am

plitu

de (d

B)

-15

-10

-5

0

Diodes "off"Diodes "on"


Measured Response - 2-inch Unit CellTransmission

Am

plitu

de (d

B)

-15

-10

-5

0

Reflection

Frequency (GHz)2 4 6 8

Phas

e (d

egre

es)

-90

-45

0

45

90

Frequency (GHz)2 4 6 8

"off" "on"


Modulated Transmission at 3.905 GHz

1 KHz square wave1 KHz sine wave


Modulated Reflection at 3.5 GHz


• 45 degree bistatic angle

• First sidelobe ~13 dB

moving target emulators for ultra wide band signals .... 2008 rome ieee uwb modulation v3 - 2....

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