Propagation of EM waves

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Propagation of EM waves
MCS.02
Maj JW Paul
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Good Judgement comes from Experience
Experience comes from Bad Judgement...
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Review
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Antenna Definition

• An antenna is defined as an efficient radiator of
  EM energy (radio waves) into free space
• transmitting and receiving antennas are
  reciprocal
• radiate watts or kilowatts
• receive microwatts or picowatts (gtnoise)
• efficiency
• tuning
• For efficiency, Ae must be at least 1/10 ?

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More Antennas

• Read lecture notes - 6Aperture.doc

Vertical monopole
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Power Loss
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Array Antennas

• Time delay
• Phase delay

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Spectrum Details
Fiber Optics
Short Wave Radio
AM Radio
Microwaves
Visible light
Mobile radio VHF TV FM Radio VHF TV
100m
10m
1m
10cm
1cm
1mm
1µm
1 MHz
10 MHz
100 MHz
1 GHz
10 GHz
100 GHz
1012Hz
MF
HF
VHF
UHF
SHF
EHF
Control of Spectrum is overseen by ITU
(International Telecommuncations Union)
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Microwave Spectrum
Military Search Radar
UHF TV
Mobile Radio
ATC Transponder
Space Telemetry Microwave heating
Airport Search Radar Microwave Relay Satcom -
downlink
Satcom - uplink
STL Microwave relay Airbrone FC radar Microwave
Relay
Satcom - downlink
Police Radar
Satcom - uplink
Missle Seeker
0.3
0.5
2
3
5
20
30
50
1 GHz
10 GHz
100 GHz
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Todays Class

• Propegation of EM Waves
• Spectral Representation of Signals

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How to get from here to there
Sky Wave
Tropospheric Wave
Direct Wave
Surface Wave
Reflected Wave
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Refraction definition

• The phenomenon occurring when waves cross a
  boundary between media in which the waves have
  different phase velocities
• This leads to a change in wavelength
• Can also lead to a change in direction of the
  wavefront

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Sky Waves
f gt fc?30-50 MHz
Sky Wave 2Mhzltflt30Mhz HF
Ionosphere
f lt flow?2 MHz (strongly attenuated)
EARTH
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Over the Horizon...
TROPOSHERE
EARTH
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Troposhperic Waves

• Waves that are reflected (scattered) at abrupt
  changes in the effective dielectric constant of
  the troposphere are known as tropospheric waves.
• Tropospheric waves are always present at all
  frequencies

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Ground Waves

• Energy propagated over all paths excluding sky
  and tropospheric waves
• Consists of space wave surface wave
• The surface wave is a wave that is guided along
  the earths surface
• The space wave is made up of the direct wave
  reflected wave
• main propagation mode for MF (300 KHz - 3 MHz -
  eg AM radio) with a range limited to roughly 200
  km

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Questions?
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Experience is what you get when you didnt get
what you really wanted
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Propagation in The Atmosphere
Ionosphere
Sky waves
100-300 km
Tropospheric wave
10 km
Troposphere
Reflected wave
Direct wave
Earth surface
The propagation of electromagnetic waves in the
atmosphere is more complicated since the energy
radiated from a transmitting antenna may reach
the receiving antenna over several possible
propagation paths
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Next Class

• Spectal Representation of Signals
• Sinusoidal (harmonics)
• Fourier Series
• Fourier Transform
• Frequency vs Time domains...