Antenna efficiency

In antenna theory, antenna efficiency is most often used to mean radiation efficiency. In the context of antennas, one often just speaks of 'efficiency.' It is a measure of the electrical efficiency with which a radio antenna converts the radio-frequency power accepted at its terminals into radiated power. Likewise, in a receiving antenna it describes the proportion of the radio wave's power intercepted by the antenna which is actually delivered as an electrical signal. It is not to be confused with aperture efficiency which applies to aperture antennas such as the parabolic reflector. Radiation efficiency is defined by IEEE Std 145-1993 'Standard Definitions of Terms for Antennas' as 'The ratio of the total power radiated by an antenna to the net power accepted by the antenna from the connected transmitter.' It is sometimes expressed as a percentage (less than 100), and is frequency dependent. It can also be described in decibels. For wire antennas which have a defined radiation resistance the radiation efficiency is the ratio of the radiation resistance to the total resistance of the antenna including ground loss (see below) and conductor resistance. In practical cases the resistive loss in any tuning and/or matching network is often included, although network loss is strictly not a property of the antenna.