Definition

decibels relative to isotropic radiator (dBi)

Part of the Telecom glossary:

The expression dBi is used to define the gain of an antenna system relative to an isotropic radiator at radio frequencies . The symbol is an abbreviation for "decibels relative to isotropic."

The dBi specification is based on the decibel , a logarithm ic measure of relative power . Suppose an antenna A produces an electromagnetic field of intensity I A microwatts per square meter ( I A µW/m 2 ) in its favored direction at a point located some distance away. Also, suppose an isotropic antenna Q produces an electromagnetic field of intensity I Q µW/m 2 at the same distance. Then the gain G of antenna A , in dBi, is:

G = 10 log 10 ( I A / I Q )

A dipole antenna has a gain of 2.15 dBi. An isotropic radiator has a gain of 0 dBi.

This was last updated in March 2011
Posted by: Margaret Rouse

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