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The unit of antenna gain is dBi. dbI means "Isotropic", a perfect POINT SOURCE, which radiates in a spherical manner. A perfect dipole radiates with a donut pattern, broadside to the long dimension of the dipole. It is a relative measurement to an ideal dipole that radiates in a perfect sphere. To achieve higher gains, antennas are constructed such that they radiate more in one direction than another. An omni directional antenna radiates uniformly in the horizontal plane and radiates very little up or down. Panel, sector, yagi, and parabolic grid antennas radiate in cones of various widths. The higher the gain, the smaller the horizontal and vertical angles. Jerm gave the sprinkler head analogy: for a given amount of water, the distance the water shoots can be increased by focusing the spray; for a given amount of of microwave energy, distance can be increased by focusing the beam.

Antennas angles are specified by their half power point (3 dbi less than the specified max output).

For example, one '14 dBi' directional antenna has 14dBi gain straight ahead but only 11 dBi gain 32 degrees horizontally and 31 degrees vertically; one '24 dBi' parabolic grid also has 24 dBi gain straight ahead but only 21 dBi gain 6.5 degrees horizontally and 10 degrees vertically.

Feedback Question:
quote:
please provide with the formula to calculate the gain of the antenna in dBi .....

A: No simple answer - see the following forum thread for more information: »Forum FAQ - pending feedback...

Feedback received on this FAQ entry:
  • dbi? & dBm? tutorial ... Email ... telrad.ec@gmail.com

    2013-02-26 05:52:27

  • ^^^ an isotropic antenna has 0 dBi

    2011-12-30 13:53:09

  • I want to know much more detail about antenna. microwave and radio wave

    2009-03-17 08:14:17

  • So is an isotropic antenna considered a gain of 0 dBi or 1 dBi?

    2009-02-05 20:04:43



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by StudMuffin See Profile edited by seagreen See Profile
last modified: 2008-03-23 10:24:45