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Free Space Materials Characterization

Shelley Blasdel Begley Application Development Engineer

Agilent Technologies

Agilent Technical ForumFree Space Materials Characterization

15 October 2008

Agenda

What is it?Free Space Measurement SystemsCalibrationMeasurement Results

Agilent Technologies


15 October 2008

What is Free Space Materials Characterization?


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Measuring Electromagnetic Properties of Materials Using Free Space Measurement Technique.

Important for:Circuit designMilitary ApplicationsCar Radar ApplicationsNew Materials ResearchIncoming Inspection Quality AssuranceHealth and Safetyand more…

Electromagnetic Materials

Radar Absorbing and Stealth Materials

Radome Materials

Electronic Substrate and Packaging Materials

Specific Absorption Rate (SAR) Phantoms


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http://en.wikipedia.org/wiki/Image:F-117_Nighthawk_flight.jpg

Transmission Free-Space System


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GP-IB or LAN

Network Analyzer

Sample holder fixtured between two antennae

Computer (not required for

PNA)

85071E Materials Measurement Software

With Option 100 Free Space Calibration

Bio-dielectrics: Theories, Mechanisms, Applications, Stamford Hall, Leicester,

UK

Lightwave Analogy

Incident

Lens


UK

Lightwave Analogy

Incident

Reflected

Lens


UK

Lightwave Analogy

Incident

Reflected

Transmitted

Lens


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Network Analyzer Block Diagram

SOURCE

Incident

Reflected

Transmitted

MUT

Fixture


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SIGNALSEPARATION

SOURCE

Incident

Reflected

Transmitted

MUT

Fixture


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RECEIVER / DETECTOR

REFLECTED(A)

INCIDENT (R)

SIGNALSEPARATION

SOURCE

Incident

Reflected

Transmitted

MUT

Fixture


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RECEIVER / DETECTOR

REFLECTED(A)

TRANSMITTED(B)

INCIDENT (R)

SIGNALSEPARATION

SOURCE

Incident

Reflected

Transmitted

MUT

Fixture


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RECEIVER / DETECTOR

PROCESSOR / DISPLAY

REFLECTED(A)

TRANSMITTED(B)

INCIDENT (R)

SIGNALSEPARATION

SOURCE

Incident

Reflected

Transmitted

MUT

Fixture

= S11Incident

Reflected Transmitted

Incident

= S21

Transmission Algorithms

(85071E also has three reflection algorithms)

Algorithm Measured S-parameters Output

Nicolson-Ross S11,S21,S12,S22r and r

Precision (NIST) S11,S21,S12,S22 r

Fast S21,S12 r

Before a Measurement Can be Made…


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Calibration is required!


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Thru

Reflect

Match

TRM Calibration

Hard to get broadband absorbers for matchHard to get broadband absorbers for match


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TRL Calibration

Thru

Reflect

Line

Move the antenna away to compensate for the thickness of the short. Move it back for the next step.

Move the antenna away on a quarter-wavelength and then back in the original position.

Precise positioning fixtures are expensivePrecise positioning fixtures are expensive

Gated Reflect Line (GRL) CalibrationTwo Tiered Process

Two port calibration at waveguide or coax input into antennas removes errors associated with network analyzer and cables.


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ECal, SOLT or TRL Cal done here

Gated Reflect Line (GRL) CalibrationTwo Tiered Process

Two additional free space calibration standards remove errors from antennas and fixture.


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Reflect

(metal plate of

known thickness)

Line

(empty fixture)

GRL Cal – How it works


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GRL Cal Error Model (forward only)

•Coax or Waveguide 2-port Cal corrects errors from end of cable back into the instrument.

2-port Cal Terms 2-port Cal Terms

D

MUT

Ms

Tr

Tt

Ml

1

S11 S22

S21

S12

GRL Error Adapter

GRL Error Adapter



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•Errors from Antennas and Fixture can be thought of as being lumped into a GRL error adapter.

•The GRL error adapter is quantified by measurements of reflect and line standards.


D

MUT

Ms

Tr

Tt

Ml

1

S11 S22

S21

S12

GRL Error Adapter

GRL Error Adapter



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Time Domain of Empty Free Space Fixture

Transmitting Antenna

Air

Receiving Antenna

gate



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•Errors from Antennas and Fixture can be thought of as being lumped into a GRL error adapter.

•The GRL error adapter is quantified by measurements of reflect and line standards.

•The original 2-port Cal is modified to correct for the error adapter.


D

MUT

Ms

Tr

Tt

Ml

1

S11 S22

S21

S12

GRL Error Adapter

GRL Error Adapter


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Free-space X-Band System

Free Space 40 – 60GHz System


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Bio-dielectrics: Theories, Mechanisms, Applications, Stamford Hall, Leicester, UK

A Simple Free Space Powder Fixture

Powder in Tray Placed Between Antennae

Close Up

Free Space 75 – 110GHz Standard Gain Horn System


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Free Space W-band System


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Free Space 75-110GHz Quasi-Optical System


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Measurement Results

Real part of EpsilonRexolite measured with 110Ghz PNA and GRL Cal

y = -3E-14x + 2.5265

2.47

2.48

2.49

2.5

2.51

2.52

2.53

2.54

2.55

2.56

2.57

7.500E+10 8.000E+10 8.500E+10 9.000E+10 9.500E+10 1.000E+11 1.050E+11 1.100E+11

frequency (hz)

e'

Std Gain Horn QO table Linear (QO table)


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Measurement Results

Imaginary part of EpsilonRexolite measured with 110Ghz PNA and GRL Cal

y = -2E-14x + 0.003

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

7.500E+10 8.000E+10 8.500E+10 9.000E+10 9.500E+10 1.000E+11 1.050E+11 1.100E+11

frequency (hz)

e"

Std Gain Horn QO table Linear (QO table)


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Conclusion


15 October 2008

Free Space is a useful method for measuring electromagnetic properties of a of materials.

Innovative calibration overcomes challenges of previous free space error correction methods.

For More Information

Visit our website at: www.agilent.com/find/materials


15 October 2008

http://www.agilent.com/find/materials

References


15 October 2008

R N Clarke (Ed.), “A Guide to the Characterisation of DielectricMaterials at RF and Microwave Frequencies,” Published by The Institute of Measurement & Control (UK) & NPL, 2003

J. Baker-Jarvis, M.D. Janezic, R.F. Riddle, R.T. Johnk, P. Kabos, C. Holloway, R.G. Geyer, C.A. Grosvenor, “Measuring the Permittivity and Permeability of Lossy Materials: Solids, Liquids, Metals, Building Materials, and Negative-Index Materials,” NIST Technical Note 15362005

“Test methods for complex permittivity (Dielectric Constant) of solid electrical insulating materials at microwave frequencies and temperatures to 1650°, ” ASTM Standard D2520, American Society for Testing and Materials

Janezic M. and Baker-Jarvis J., “Full-wave Analysis of a Split-Cylinder Resonator for Nondestructive Permittivity Measurements,” IEEE Transactions on Microwave Theory and Techniques vol. 47, no. 10, Oct 1999, pg. 2014-2020

J. Krupka , A.P. Gregory, O.C. Rochard, R.N. Clarke, B. Riddle, J. Baker-Jarvis, “Uncertainty of Complex Permittivity Measurement by Split-Post Dielectric Resonator Techniques,” Journal of the European Ceramic SocietyNo. 10, 2001, pg. 2673-2676

“Basics of Measureing the Dielectric Properties of Materials”. Agilent application note. 5989-2589EN, April 28, 2005

mm-Wave Free Space Results


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Rexolite expected

value

e’ = 2.53

Apendix


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• • • •Section Title

GRL Cal – System Considerations


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•Determine Sample Position

•Determine Sample Size

•Choose Metal Plate

Fixture with Metal Plate

Metal Plate

GRL Cal - Considerations


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Transmitting Antenna

20nS

Receiving Antenna

• Choose Number of points to Avoid Aliasing

Empty Fixture

Minumum Number of Points =

1 + Range * (Stop Frequency – Start Frequency)

Where Range is the needed alias free range in Seconds

GRL Cal - Considerations


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• Choose Time Domain Parameters

Empty Fixture Fixture with Metal Plate

Metal Plate at 3.5nS

Air at 3.5nS


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Quasi Optical System Schematic

Additional information available at : http://www.terahertz.co.uk/TKI/Agilent/Agilent_VNA_QO.html

MUT and GRL Error Adapters

After 2-Port Calibration


15 October 2008

MUT

S11 S22

S21

S12

T22 T11

T12

T21

O11 O22

O21

O12

Six Unknowns

021 = O12

O11

O22

T21 = T12

T11

T22

MUT and GRL Error Adapters

After O11 and T11 are embedded into the original 2-Port calibration.


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MUT

S11 S22

S21

S12

T22

T12

T21

O22

O21

O12

Four Unknowns

O21 = O12

O22

T21 = T12

T22

GRL Metal Plate Standard


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P11 = P22 = -1

P21=P12=0.

21 12plate_1

22

O O

1 O

21 12plate_2

22

T T

1 T

MUT

S11 S22

S21

S12

T22

T12

T21

O22

O21

O12

GRL Thru Standard (Air)


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A11=A22=0

A21 = A12 =

= frequency= permittivity of air= permeability of air.d= thickness of the metal plate

21 12 21 12 22air_1

22 22

A A O O T

1 O T

21 12 21 12 22air_2

22 22

A A T T O

1 T O

j ude

MUT

S11 S22

S21

S12

T22

T12

T21

O22

O21

O12

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