# Antenna Directivity Calculator

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 (PR) by the antenna to the power delivered (PD) to it. The theoretical maximum value is 1 when it radiates all the power delivered to it

η = PR/PD

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.