Antenna Gain - Relative to a Dipole


In electromagnetics, an antenna’s power gain or simply gain is a key performance figure which combines the antenna’s directivity and electrical efficiency. As a transmitting antenna, the figure describes how well the antenna converts input power into radio waves headed in a specified direction. As a receiving antenna, the figure describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, “gain” is understood to refer to the peak value of the gain. A plot of the gain as a function of direction is called the radiation pattern.



A true isotropic radiator cannot be built, so in practice a different antenna is used. This will often be a half-wave dipole, a very well understood and repeatable antenna that can be easily built for any frequency. The directive gain of a half-wave dipole is known to be 1.64 and it can be made nearly 100% efficient. Since the gain has been measured with respect to this reference antenna, the difference in the gain of the test antenna is often compared to that of the dipole. The “gain relative to a dipole” is thus often quoted and is denoted using “dBd” instead of “dBi” to avoid confusion. Therefore in terms of the true gain (relative to an isotropic radiator) G, this figure for the gain is given by the formula shown here.

Related formulas


GdBdantenna gain relative to a dipole (in dB) (dimensionless)
Gtrue gain (dimensionless)