It is not to be confused with antenna efficiency, which applies to aperture antennas such as a parabolic reflector or phased array, or antenna/aperture illumination efficiency, which relates the maximum directivity of an antenna/aperture to its standard directivity.
For other types of antenna the radiation efficiency is less easy to calculate and is usually determined by measurements.
[5] This dependence is always present, but it is easier to interpret in the case where the interactions between the ports are sufficiently small.
as design parameter is particularly relevant to a multiport antenna array intended for MIMO transmission with spatial multiplexing, and that using
as design parameter is particularly relevant to a multiport antenna array intended for beamforming in a single direction or over a small solid angle.
[8][9] The Wheeler method uses two impedance measurements, one of which with the antenna located in a metallic box (the cap).
Unfortunately, the presence of the cap is likely to significantly modify the current distribution on the antenna, so that the resulting accuracy is difficult to determine.
Thus, the Q factor method is only semi-experimental, because it relies on a theoretical computation using an assumed geometry of the actual antenna.
Other radiation efficiency measurement techniques include: the pattern integration method, which requires gain measurements over many directions and two polarizations; and reverberation chamber techniques, which utilize a mode-stirred reverberation chamber.
[8][10] The loss of radio-frequency power to heat can be subdivided many different ways, depending on the number of significantly lossy objects electrically coupled to the antenna, and on the level of detail desired.
For vertical monopoles and other antennas placed near the ground, ground loss occurs due to the electrical resistance encountered by radio-frequency fields and currents passing through the soil in the vicinity of the antenna, as well as ohmic resistance in metal objects in the antenna's surroundings (such as its mast or stalk), and ohmic resistance in its ground plane / counterpoise, and in electrical and mechanical bonding connections.