User's Manual
Antenna Evaluation
February 2004 13
3.1.2 Antenna Gain
Gain is the ability of an antenna to amplify received and transmitted signals. Numerically, it is the
comparison between an antenna’s maximum signal strength and the signal strength of a laboratory
standard.
3.1.2.1 dBi (Decibels Relative to Isotropic)
An antenna’s gain specification normally appears as a decibel value. The decibel scale is a logarithmic
scale used for representing comparative signal strengths; it is the ratio of one signal compared to a second
signal.
When describing antenna gain, “decibel” is abbreviated as “dBi” (decibels relative to isotropic).
“Relative” signifies that this measurement is a comparison between the antenna’s signal and a second
signal, and “isotropic” indicates that the second signal is the theoretical ideal laboratory standard.
For example, the network uses two different omni antennas having gains of 2.5 dBi and 6.0 dBi, and two
different sector antennas with gains of 10 dBi and 13 dBi.
Note: You will also see “decibel” abbreviated as “dB” (without the “i”). “dB”
signifies that a signal’s strength is being compared to the strength of a second
signal that is not the laboratory standard. For example, “dB” is used when
describing the relative strengths of a signal in different parts of a signal pattern.
(See section 3.3.2.1.)