# Antenna Power Gain

on . Posted in Telecommunications Engineering

Power gain of an antenna is a measure of how effectively the antenna directs the radio frequency (RF) power it receives into a particular direction compared to a reference antenna, usually an isotropic antenna (one that radiates power uniformly in all directions).  It is expressed as a ratio of the power radiated in a specific direction to the power radiated by the reference antenna, both antennas being fed with the same input power.  An antenna with a higher power gain will focus more power in a specific direction, which is beneficial in applications where long-distance communication is required.  For example, directional antennas such as parabolic dishes or Yagi antennas have high gains, while omnidirectional antennas have lower gains because they spread power more evenly in all directions.

### Types of Gain Types

Absolute gain ($$G$$)  -  Measures the gain relative to an isotropic antenna.

Relative gain ($$dBi$$)  -  Gain relative to an isotropic antenna, where $$\; G_{dBi} = G \; in \; dB$$.

Gain relative to dipole ($$dBd$$)  -  This is the gain relative to a standard dipole antenna.

### Anrenna Power Gain formula

$$G_{dBi} \;=\; 10 \; log \;( P_{out} \;/\; P_{in} )$$
Symbol English Metric
$$G_{dBi}$$ = Power Gain given in decibels $$dB$$ $$dB$$
$$P_{out}$$ = Power Radiated in the Direction of Interest $$W$$ $$kg-m^2\;/\;s^3$$
$$P_{in}$$ = Input Power to the Antenna $$W$$ $$kg-m^2\;/\;s^3$$

Tags: Communication System