A Portable Demo SetUp
for Teaching of
Antennas and EM Wave Propagation
Phenomena
J. R. Mosig, J.-F. Zurcher, S. Bruegger
Laboratory of Electromagnetics & Acoustics
Ecole Polytechnique Fédérale de Lausanne
(LEMA-EPFL)
juan.mosig@epfl.ch http://itopwww.epfl.ch/LEMA
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
1
Educating Engineering Students in
Antennas and ElectroMagnetic Waves
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
2
How dangerous are the
ElectroMagnetic waves ?
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
3
If we make the identification
Electromagnetic waves = Rain
Frequency = drops’ size ; Power = drop’s density
Low Frequency
Low Power
Low Frequency
HIgh Power
Telecom
Microwave
Oven
High Frequency
Low Power
High Frequency
High Power
Medical
X-rays
Tchernobyl
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
4
We need antennas
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
5
ANTENNAS (ANTENNES) AND FUNNELS (ENTONNOIRS)
Some antennas (horns) look like « funnels » for EM
waves
Other (wire antennas for cellulars) not at all
Is this a
funnel?
Are EM waves affected by antennas like liquids are
affected by funnels?
Bad!
Decent
Very good!
Rx Antenna / Funnel
Bad!
No Antenna / Funnel
Very good
Better!
Really stupid!
Tx Antenna / Funnel
Good!
Tx&Rx Antenna/Funnel
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
6
Problem:
Reception of a message sent through EM
waves is too weak
>>>>>>>
Solution #1: We increase the amplification
of the associated electronics
(« volume knobs»).
> Higher electricity bill
> Higher EM radiation
>>>>
Solution #2 : We use good antennas
> Reduced electricity bill
> Mastered EM radiation
ANTENNAS ARE ECOLOGICAL AMPLIFIERS !!
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
7
Antenna Gain vs Amplifier Gain
• An Antenna is frequently a passive system
• Its « Gain » measures its capacity of
concentrating radiation in a given direction
• 20 to 30 dB are respectable values for
antenna gain (compare with Op Amps)
• At 178 meters, 100 watts yield an average
of 1 mW/m2 without antenna, but a 20 dB
antenna can provide100 mW/m2 in a given
direction
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
8
A FAKE SATELLITE TX-RX SYSTEM
in an EARTH LABORATORY:
THE MICROWAVE SUITCASE
• Demonstrate basic Elec. Eng system
principles
• Illustrate Wireless Comm. Systems
• Allow understanding of basic Antenna&EM
wave phenomena like:
– Reflection and Diffraction
– Antenna Gain & Directivity
– Polarization
–…
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
9
DC Power
Generation
& Stockage
Power Engineering
DC volts&amperes
Electronic Engineering
Oscillator
AC volts&amperes
Modulator
External
Signal
AC volts&amperes
Signal Engineering
Antenna
AC E&H fields
BUILDING
A
NANO
SATELLITE
BEACON
IN
AN
ELECTRICAL
ENGINEERING
DEPT.
RF Engineering
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
10
A more realistic version
Transmitter
Receiver
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
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The final suitcase
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
12
The Polarization of EM waves
Ask a student which orientation will he give to
his stick when throwing it if the window has only
vertical bars
An EM wave passes through metallic bars
if its H-field is parallel to the bars:
the magnetic field is the « stick » of the wave
that can « slide » between the bars
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
13
Understanding the Polarization of EM waves - 1
CONFIRMATION DU CARACTERE
"ONDE TRANSVERSE"
EN INTERCALANT UNPOLARISEUR
CELA se comporte
comme un jet de
corpuscules ?
Transmission à
travers le polariseur
Ou CELA se comporte
comme une onde
transverse ?
FAIT EXPERIMENTAL (POLARISATION)
Cornets alignés:
transmission
Pas de transmission
avec le polariseur
tourné de 90 degrés
Cornets à 90 degrés:
Pas de transmission
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
14
Understanding the Polarization of EM waves - 2
CONFIRMATION DU CARACTERE
"ONDE TRANSVERSE"
EN INTERCALANT UNPOLARISEUR
ET SI LE POLARISEUR EST À 45 DEGRES ?
Transmission à
travers le polariseur
?
L'onde connaît
l'algèbre vectorielle !
Pas de transmission
avec le polariseur
tourné de 90 degrés
Le cornet récepteur ne
prendra que la partie
verticale de l'onde qui a
traversé le polarisateur,
soit finalement 25% de
la puissance de départ
J. Mosig / EWME 2004, EPF Lausanne, April 15-16, 2004
Elle se projète sur le
polariseur (produit
scalaire) et se divise en
deux: seulement la
partie parallèle est
transmise: 70% en
amplitude, soit 50% en
puissance
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