Fundamentals of Transmission channels

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Fundamentals of Transmission channels

• Introduction to Microwave
• Introduction to Mobile Radio Channels
• Large-scale path loss
• Small-scale fading and multipath

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Introduction to Microwave

• All electronic communications systems send
  information from one point to another by
  transmitting electromagnetic energy from the
  sender to the intended receiver.
• This electromagnetic energy can travel in various
  modes,

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Velocity, Frequency, and Wavelength

• Velocity of an electromagnetic (EM) wave in free
  space (vacuum)
• where µ0 is the permeability of free space and e0
  is the permittivity of free space. They are the
  distributed values of L and C of free space.

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• Absolute permittivity of a medium is noted as e
  and is given by e er e0
• where er is the relative permittivity
  (dielectric constant).
• Absolute permeability of a medium is noted as µ
  and is given by µ µr µ0
• where µr is the relative permeability, equaling
  to 1 for a vacuum and most nonmagnetic metals.
  Thus, µr equals 1 for most purposes.
• If the wave travels through a medium of er, the
  new velocity is vr C/ er1/2
• where c 3.0x108 m/s is the velocity of light
  in vacuum.

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Frequency and Wavelength

• Frequency f is the number of cycles per second a
  signal contains.
• Signal (wave) period T is the time of one
  complete cycle, i.e. T 1/f
• Wavelength ? of an EM wave is the physical
  distance the wave travels in one cycle,
• i.e., ? c/f (in free space)
• Example 2 caculate the wavelength ? for an EM
  wave f50GHz where er3.0.

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The Electromagnetic Spectrum
The total span of frequencies and corresponding
wavelengths used in communications systems is
called the electromagnetic spectrum. The overall
useful electromagnetic spectrum extends from
about 10,000Hz to several billion hertz.
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Microwaves

• Microwaves are electromagnetic radiation of
  frequencies from several hundred MHz to several
  hundred GHz.

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