Lecture 2: Radio Wave Propagation

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Lecture 2Radio Wave Propagation

• Anders Västberg
• 08-790 44 55
• vastberg_at_kth.se

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Maxwell's Equations
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Maxwell's Equations

• Electrical field lines may either start and end
  on charges, or are continuous
• Magnetic field lines are continuous
• An electric field is produced by a time-varying
  magnetic field
• A magnetic field is produced by a time-varying
  electric field or by a current

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Radiation
Uniform motion
Reversing direction
Direction change
Osscillating periodic motion
Only accelerating charges produce radiation
Saunders, 1999
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Propagation Mechanisms

• The higher frequency
• The more radio waves resamble the properties of
  light
• At lower frequencies
• Electrical properties of obstacles are important
  (but we tend to express these in terms of optical
  properties)
• If the wave length is of the same order of
  magnitude (or larger), diffraction or surface
  effects dominate

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Propagation mechanisms

• When the dimension of the object is
• Very Large compared to the wavelength
• Reflection
• Larger compared to the wavelength
• Diffraction
• Small compared to the wavelength
• Scattering
• Very small compared to the wavelength
• Unaffected

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Diffraction
Saunders, 1999
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Propagation between two antennas (not to scale)
No Ground Wave for Frequencies gt 2 MHz No
Ionospheric Wave for Frequencies gt 30 Mhz
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Free Space Propagation
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Knife edge loss
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Effective Earth Radius
Re8500 km4/3R0
Slimane
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Fresnel Zones