Directivity is a measure of how much the energy radiated by an antenna is concentrated in any single direction. Mathematically, It is the ratio of the radiation intensity in a given direction to the radiation intensity averaged over all directions.

Directivity is calculated as a ratio of the antenna gain to its efficiency

**D = G/η **

Antenna Efficiency (**η**) is the ratio of power radiated (**P _{R}**) by the antenna to the power delivered (

**P**) to it. The theoretical maximum value is 1 when it radiates all the power delivered to it

_{D}**η = P _{R}/P_{D}**

The theoretical maximum value is 1 when the antenna radiates all the power delivered to it. This is an ideal situation and in practice a well-designed and manufactured antenna will only radiate up to a maximum of 60% of the input power.

Note that this power loss is in addition to the mismatch loss and should be accounted for when making a range calculation. You can simply add it to the Cable and other losses.

**Frequently Asked Questions**

**What is the directivity of an isotropic Antenna?**

The directivity of an isotropic antenna is 1. An isotropic antenna radiates equally in all directions. Its Efficiency is 1 or 100% and its Gain is 0 dBi.