What is dBi, dBd, dBu ?

What is dBi ?

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 .

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.

What is dBd ?

dBd (decibels related to dipole antenna) is a measure of the gain of an antenna system relative to a dipole antenna at radio frequency.

The dBd specification is based on the decibel, a logarithmic measure of relative power. Suppose an antenna A produces an electromagnetic field of intensity IA microwatts per square meter (µW/m2) in its favored direction at a point located a defined distance away. Also, suppose a half-wave dipole antenna D produces an electromagnetic field of intensity ID µW/m2 in its favored direction at the same distance. Then the gain G of antenna A, in dBd, is:

G = 10 log10 (IA / ID)

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

What is dBu ?

dBu can be used as a measure of voltage, regardless of impedance, but is derived from a 600 Ω load dissipating 0 dBm (1 mW)