abid saleem

Mar 18th, 2013

Antenna gain relates the intensity of an antenna in a given direction to the intensity that would be produced by a hypothetical ideal antenna that radiates equally in all directions (isotropically) and has no losses. Since the radiation intensity from a lossless isotropic antenna equals the power into the antenna divided by a solid angle of 4π steradians, we can write the following equation:

Although the gain of an antenna is directly related to its directivity, the antenna gain is a measure that also takes into account the efficiency of the antenna, that is, the fraction of the input power dissipated in losses such as resistance. In contrast, directivity is defined as a measure that takes into account only the directional properties of the antenna and therefore it is only influenced by the antenna pattern. However, if we assumed an ideal antenna without losses then antenna gain will equal directivity as the antenna efficiency factor equals 1 (100% efficiency). Therefore, for real antennas, the gain of an antenna is always less than its directivity.