Gain (antenna)

In <a href="/facts/Electromagnetics/oAkmALHT">electromagnetics</a>, an antenna's gain is a key performance parameter which combines the <a href="/facts/Antenna_(radio)/pGlcXBvc">antenna</a>'s <a href="/facts/Directivity/ELvBJQu6">directivity</a> and <a href="/facts/Radiation_efficiency/zvFLeTjH">radiation efficiency</a>. The term power gain has been deprecated by IEEE. In a transmitting antenna, the gain describes how well the antenna converts input power into <a href="/facts/Radio_wave/XmB6WPpF">radio waves</a> headed in a specified direction. In a receiving antenna, the gain 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, the gain in the direction of the antenna's <a href="/facts/Main_lobe/sjXsb6Gv">main lobe</a>. A plot of the gain as a function of direction is called the antenna pattern or <a href="/facts/Radiation_pattern/5t0QU2mv">radiation pattern</a>. It is not to be confused with directivity, which does not take an antenna's radiation efficiency into account.
Gain or 'absolute gain' is defined as "The ratio of the radiation intensity in a given direction to the radiation intensity that would be produced if the power accepted by the antenna were isotropically radiated". Usually this ratio is expressed in <a href="/facts/Decibels/0LyxAPXh">decibels</a> with respect to an <a href="/facts/Isotropic_radiator/HFGgrM74">isotropic radiator</a> (dBi). An alternative definition compares the received power to the power received by a lossless <a href="/facts/Dipole_antenna/GYWgnX72">half-wave dipole antenna</a>, in which case the units are written as dBd. Since a lossless dipole antenna has a gain of 2.15 dBi, the relation between these units is 
 
 
 
 
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 {\displaystyle \mathrm {Gain(dBd)} \approx \mathrm {Gain(dBi)} -2.15}
 
. For a given frequency, the antenna's <a href="/facts/Effective_area/rAHTKdP6">effective area</a> is proportional to the gain. An antenna's <a href="/facts/Antenna_aperture/rAHTKdP6">effective length</a> is proportional to the square root of the antenna's gain for a particular frequency and <a href="/facts/Radiation_resistance/VRdjWPpL">radiation resistance</a>. Due to <a href="/facts/Reciprocity_(electromagnetism)/ugX6mhH9">reciprocity</a>, the gain of any antenna when receiving is equal to its gain when transmitting.

Gain (antenna) open-in-new

Gain (antenna)