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Lecture 2: Radio Wave Propagation

Lecture 2: Radio Wave Propagation. Anders Västberg 08-790 44 55 vastberg@kth.se. Maxwell's Equations. Maxwell's Equations. Electrical field lines may either start and end on charges, or are continuous Magnetic field lines are continuous

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Lecture 2: Radio Wave Propagation

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  1. Lecture 2:Radio Wave Propagation Anders Västberg 08-790 44 55 vastberg@kth.se

  2. Maxwell's Equations

  3. 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

  4. Radiation Uniform motion Reversing direction Direction change Osscillating periodic motion Only accelerating charges produce radiation [Saunders, 1999]

  5. 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

  6. 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

  7. Diffraction [Saunders, 1999]

  8. Propagation between two antennas (not to scale) No Ground Wave for Frequencies > ~2 MHz No Ionospheric Wave for Frequencies > ~30 Mhz

  9. Free Space Propagation

  10. Knife edge loss

  11. Effective Earth Radius Re=8500 km=4/3R0 [Slimane]

  12. Fresnel Zones

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