Directivity is the ratio of the radiation intensity in a given direction from the
antenna in relation to the radiation intensity averaged over all directions.

If the main direction of radiation is known, the directivity $D$ can be calculated for each antenna pattern with the following
equation:

If the antenna pattern consists of a discrete number of values, the integrals in the
equations must be substituted with a summation with increments $\Delta \vartheta $ and $\Delta \phi $ :

Often the directivity of an antenna is given in dB. The logarithmic value ${D}_{db}$ in dB can be obtained from the linear value $D$ of the directivity with the following equation: