Antenna Primer

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Antenna Primer

• Wang Ng

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References

• Balanis Antenna Theory
• Collin Antennas and Radiowave Propagation

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What is an antenna?

• The American Heritage Dictionary A metallic
  apparatus for sending and receiving
  electromagnetic waves.
• Websters Dictionary A usually metallic device
  (as a rod or wire) for radiating or receiving
  radio waves.
• Balanis Antenna Theory An antenna is a
  transitional structure between free-space and a
  guiding structure.
• Assumption Lossless antennas

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Types of Antennas

• Wire antennas
• Aperture antennas
• Array antennas
• Reflector antennas
• Lens antennas
• Patch antennas

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Radiation Mechanism
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Basic Antenna Parameters

• Radiation pattern The relative distribution of
  radiated power as a function of direction in
  space an (hypothetical) isotropic antenna
  radiates equally in all directions.
• Gain G The ratio of the radiated power in the
  maximum direction to the radiated power of an
  isotropic antenna. The gain of an antenna
  represents the ability to focus its beam in a
  particular direction an isotropic antenna has a
  gain of 0 dB.

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Basic Antenna Parameters

• Radiation Resistance RA The equivalent
  resistance which would dissipate the same amount
  of power as the antenna radiates.
• Input impedance ZA The ratio of the voltage to
  the current at the antenna terminals (Thevenin
  equivalent circuit).
• Polarization The direction of the E-field.

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Basic Antenna Parameters

• Beamwidth The angle between the two directions
  in which the radiated power is half of the
  maximum value of the beam.
• Bandwidth Half-power frequency band.
• Antenna efficiency e Prad / Pin
• Effective aperture It describes the
  effectiveness of an antenna in the receiving
  mode. It is defined as the ratio of the power
  delivered to the load to the incident power
  density.

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Friis Transmission Equation

• For polarization matched antennas aligned for
  maximum directional radiation and reception, the
  ratio of the transmitted and received power is

Space Loss Factor
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Radiation Pattern of an Infinitesimal Dipole
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Radiation Pattern of a Thin Dipole
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Radiation Pattern of a Circular Loop