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• Free-space

  Propagation of electromagnetic waves Often called radio-frequency (RF) propagation or simply radio propagation
• Electromagnetic waves

  Electrical energy that has escaped into free space
• Polarization

  The orientation of the electric field vector in respect to the surface of the Earth
• Linear Polarization


  Polarization remains constant
• Forms of Linear polarization

  • Horizontal Polarization
  • Vertical Polarization
• Circular Polarization


  Polarization vector rotates 360◦ as the wave moves one wave-length through the space and the field strength is equal at all angles of polarization
• Elliptical Polarization


  Field strength varies with changes in polarization
• Rays


  Used to show the relative direction of electromagnetic wave propagation
• Wavefront


  Formed when two points of equal phase on rays propagated from the same source are joined together
• Point source


  A single location from which rays propagate equally in all directions
• Magnetic Field


  Invisible force field produced by a magnet, such as a conductor when current is flowing through
• H=1/2pid

  Strength of a magnetic field (H) produced around a conductor is expressed mathematically as:
• Electric fields


  Invisible force fields produced by a difference in voltage potential between two conductors
• E = q/4piEd^2

  Electric filed strength (E) is expressed mathematically as:
• Permittivity


  Dielectric constant of the material separating the two conductors
• The permittivity of air or free space is approximately 8.85 x 10 -12 F/m
• Power density


  The rate at which energy passes through a given surface area in free space
• Field intensity


  Intensity of the electric and magnetic fields of an electromagnetic wave propagating in free space
• Power density


  Mathematically expressed as: P = €H W/m2
• Characteristic impedance


  The characteristic impedance of a lossless transmission medium is equal to the square root of the ratio of its magnetic permeability to its electric permittivity
• Isotropic radiator


  Point source that radiates power at a constant rate uniformly in all directions
• Inverse Square Law


  Power density is inversely proportional to the square of the distance from the source
• Isotropic medium


  Propagation medium
• Attenuation


  Waves propagate through free space, they spread out, resulting in a reduction in power density
• Absorption Loss


  Reduction of Power
• Wave attenuation


  Reduction in power density with distance is equivalent to a power loss
• Space attenuation


  Spherical spreading of the wave
• Homogeneous medium


  One with uniform properties throughout
• Inhomogeneous medium


  Absorption coefficient varies considerably with location, thus creating a difficult problem for radio systems engineers
• Optical properties of Radio Waves

  • Refraction
  • Reflection
  • Diffraction
  • Interference
• Refraction


  Bending of the radio wave path
• Refractive index


  Square root of the dielectric constant and is expressed as: n = (k)
• Dielectric constant relative to free space (vacuum)

  K = (1- 81N/f2)1/2
• Plane


  Boundary between two media with different densities
• Normal


  Imaginary line drawn perpendicular to the interface at the point of incidence
• Angle of Incidence


  Angle formed between the incident wave and the normal
• Angle of Refraction


  Angle formed between the refracted wave and the normal
• Refractive Index


  Ratio of velocity of propagation of a light ray in free space to the velocity of propagation of a light ray in a given material
• Density gradient


  Perpendicular to the direction of propagation (parallel to the waveform)
• Reflect


  To cast or turn back