Modeling Microwave Transmission Lines with Wide Dielectric Permittivity Ranges

1
Modeling Microwave Transmission Lines with Wide
Dielectric Permittivity Ranges

• Michael Lei
• Faculty Mentor Andre Knoesen, Ph.D. Diego
  Yankelevich, Ph.D.
• Graduate Student Advisor Qin Chen Cameron
  Blatter
• Department of Electrical and Computer Engineering
• University of California, Davis

2
Overview

• Background
• Present Study
• Method
• Result
• Discussion
• Next Step

3
Background

• The experimental data of non-standard strip
  transmission line and non-standard coplanar
  waveguide transmission line were obtained
• To date, few simulations have been performed
  using these two models

4
Present Study

• Used Ansofts High Frequency Structure Simulator
  to obtain effective dielectric constant and
  characteristic impedance for non-standard
  stripline transmission lines and S-parameters for
  non-standard coplanar waveguide.

5
Software

• Ansoft High Frequency Structure Simulator (HFSS)
• Finite Element Method
• Can simulate different types of transmission
  lines with multiple layer of dielectric
• Capable of S-parameters, impedance and
  propagation constant calculation

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Stripline Method

• Stripline virtual model

Liquid Sample
Air
Duroid
Signal Strip
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Stripline Method

• Stripline virtual model

Sample
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Stripline Method (cont.)

• Stripline Setup
• Frequency Range
• 0.5GHz 5GHz
• Lose Tangent
• 0.01
• Simulated Relative Dielectric Constant of the
  sample
• 1, 2.5, 5, 6.5, 8, 10, 12.5, 15, 20, 40, 60, 80
  

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Stripline Method(cont.)

• Useful Parameters Obtained from HFSS
• Port Input Impedance (Z0)
• Propagation Constant (?)

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Stripline Methods(cont.)

• De-embing Effective Dielectric Constant
  (?eff)from ?
• ? ? - j? ? sqrt(?o ?eff?o)
• where ?o 4?10-7 H/m
• ?o 8.85410-12 F/m

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Stripline Method(cont.)

• Solving for ?eff, we have
• Re?eff (?2 - ?2)/ (?2?o?o)
• Im?eff (-j2??)/(?2?o?o)

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Stripline Results

• HFSS Design Curve

Graph provided by the Courtesy of Cameron Blatter
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CPW Method

• Coplanar WaveGuide Virtual Model

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CPW Method (Cont.)
Signal Strip
Ground
Ground
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CPW Method (Cont.)

• XXX Eqs.

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CPW Method(Cont.)

• Coplanar Waveguide setup
• 20 chosen ?r values and loss tangent values
  corresponding to specific frequencies for
  methanol and water were entered into the HFSS
  simulator to determine the S-parameters of port 1
  and port 2.
• Using Matlabs function spline(x,y,xx) to
  interpolate the missing data in between each
  chosen value.

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CPW Method (cont.)

• Some background information
• S11 input complex reflection coefficient
• S21 forward complex transmission coefficient

Transmitted
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CPW Results

• Methanol

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CPW Results (cont.)
Water
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Stripline Discussion

• ?r increases ? Zo decreases
• ?r increases ? ?eff increases
• Design Curves

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CPW Discussion

• Coplanar Waveguide
• S-parameters comparison

Miscellaneous connectors, side of the device,
and etc
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Limitation

• HFSS Accuracy
• Frequency range near the reference frequency
• Frequency range away from the reference frequency
• Hard disk space, speed of CPU.

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Limitations

• HFSS
• Pick a value of dielectric constant corresponding
  to the frequency from the water curve (Dielectric
  constant cant enter as a function of frequency)
• Outside the reference frequency, it will be off
  quite a bit.
• 41 dielectric constant were picked

24
Future Studies

• Stripline
• CPW
• Include the miscellaneous parts into the
  simulation
• Obtain a design curve of Zo, ?eff and ?r

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Modeling Microwave Transmission Lines with Wide
Dielectric Permittivity Ranges

• Michael Lei
• Faculty Mentor Andre Knoesen, Ph.D. Diego
  Yankelevich, Ph.D.
• Graduate Student Advisor Qin Chen Cameron
  Blatter
• Department of Electrical and Computer Engineering
• University of California, Davis