DESIGN AND SIMULATION OF A TEM SENSOR FOR · PDF fileNicolas Mora, Top Mor Diabou, ... ZZ h t...

EPFL-STI-SCI-FR, EMC Group http://emc.epfl.ch

DESIGN AND SIMULATION OF A TEM SENSOR FOR ELECTRIC FIELD IMPULSE

MEASUREMENTS

Nicolas Mora, Top Mor Diabou, Farhad Rachidi Swiss Federal Institute of Technology – EPFL

CST Workshop 2011

Freising, Germany

May 17th – May 19th

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DESIGN AND SIMULATION OF A TEM SENSOR FOR ELECTRIC FIELD IMPULSE MEASUREMENTS

OUTLINE

1. TEM sensor overview

2. TEM sensor input impedance

3. TEM sensor impulse response

4. Future Work

5. References

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TEM SENSOR OVERVIEW

• Very simple design

• Easy to build

• Broadband

• Applications: - IRAs - Short pulse radars - E-field sensors

Image taken from [1]

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TEM SENSOR OVERVIEW

• Completely described by three variables: - Aperture angle α - Elevation angle β - Antenna length L

L: length

α

Aperture angle

β

Elevation angle

w

h

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TEM SENSOR INPUT IMPEDANCE

• Several analytic formulations [2]

• For small aperture and elevation angles, microstrip approximation is valid

0

2 2

sin( )22arctan( )

2

A=

8 22

2 2[ 1 ln( 1)] 2

c

A A

w

hZ

ww e e hh w

A A h

β

α

πη

π ππ

−

=

< −= − − − >

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• Several analytic formulations [2]

• For small aperture and elevation angles, microstrip approximation is valid

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• L>3λmax [3] • Antenna length is

chosen based on mechanical constraints

L: length

α

Aperture angle

β

Elevation angle

w

h

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• The antenna was built in CST for making parametric analyses

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• Coaxial feeding was emulated by using a waveguide port

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• Built in TDR signal was used as voltage excitation

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• Built in TDR signal was used as voltage excitation

Input connector

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L: length

α

Aperture angle

β

Elevation angle

w

h

• Final dimensions: - α = 20° - β = 4° - L = 1m

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TEM SENSOR IMPULSE RESPONSE

• Za: impedance on TEM feed of the antenna

• Z0: Free space wave impedance

• Zc: waveguide impedance

( )recV t

aZcZ0Z

( )incE t

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( )recV t

aZcZ0Z

( )incE t

0

0

( ) ( )( )

( ) ( )

2

rec inc

Nc

pN

g

c ap

c a

ag

V t E th tZ Z

h t h tf

Z ZZ ZZfZ

τ

τ

=

=

=+

=

See [4] for further details

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( )recV t

aZcZ0Z

( )incE t

0 ( )( )( )

rec

N incc

Z VhZ E

ωωω

=


• The normalized impulse response can be obtained in the frequency domain:

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( )recV t

aZcZ0Z

( )incE t


• Once hN(t) is found, h(t) can be extracted if τp and fg are known

0

0

Ideally 1, and

Thus, ( ) ( )

cp g

Nc

ZfZ

Zh t h tZ

τ = =

=

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( )recV t

aZcZ0Z

( )incE t

See [4], [5] for further details

• A convolution with an impulse like function can be approximated to a multiplication by the area under the impulse

( ) ( )

( ) ( )

a

a

rec inccN

o

pN N

impulse impulseg

ZV t h E tZ

h h t dt h t dtf

τ

≈

= =∫ ∫

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( )recV t

aZcZ0Z

( )incE t

See [4], [5] for further details

• This integral is equal to half the plate separation in the TEM horn [5]

( )2

( ) ( )2

impulse

rec inc

hh t dt

hV t E t

=

≈

∫

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• The impulse response was evaluated by illuminating the TEM sensor with a plane wave

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• The excitation was an impulse like waveform (gaussian)

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• A butterworth filter with N=20 and fo =3GHz was used to remove noise

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• Theoretical and simulated waveforms are in good agreement

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• Theoretical and simulated integrals are in good agreement

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FUTURE WORK

• Experimental validation of the design

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REFERENCES

[1] Farr-Research Inc. Catalog, available at: http://www.farr-research.com/FRI_Catalog.pdf [2] R. T. Lee and G. S. Smith, "On the Characteristic impedance of the TEM horn antenna," Antennas and Propagation, IEEE Transactions on, vol. 52, 2004,pp. 315-318. [3] R. T. Lee and G. S. Smith, "A design study for the basic TEM horn antenna," Antennas and Propagation Magazine, IEEE, vol. 46, 2004,pp. 86-92. [4] E. G. Farr and C. A. Frost, "Compact Ultra-Short Fuzing Antenna Design and Measurements," C.E. Baum Sensor and Simulation Notes, vol. 380, 1995.

[5] C. E. Baum, "Aperture Efficiencies for IRAs," C.E. Baum Sensor and Simulation Notes, vol. 328, 1991.

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http://www.farr-research.com/FRI_Catalog.pdf



DESIGN AND SIMULATION OF A TEM SENSOR FOR · PDF fileNicolas Mora, Top Mor Diabou, ... ZZ h t...

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