# Antenna efficiency

Antenna efficiency, η, is a term associated with aperture antennas, e.g., parabolic dishes. Antenna efficiency is different from and contrasted with radiation efficiency, which applies to any antenna type.

## Definition

Antenna efficiency is defined as the ratio of the aperture effective area, Ae to its actual physical area, A.[1] It describes the percentage of the physical aperture area which actually captures radio frequency (RF) energy. Thus, the effective area of an aperture antenna is the surface area of a theoretically perfect aperture that would collect the same energy as the actual aperture with associated antenna efficiency.

${\displaystyle A_{e}=A\eta }$

Effective area is an important concept in the study of antennas, because the ratio of the gain of an antenna to its effective area can be shown to be a universal constant.[2]

## Other definitions of efficiency in antennas

IEEE defines several other antenna parameters which include the word efficiency, such as

• aperture illumination efficiency for aperture-antennas.
• polarization efficiency; polarization mismatch factor.

These are closely related and easily misunderstood definitions. Care must be taken in engineering applications to ensure that the efficiency specifications are specific, clear, and unambiguous.

## References

1. ^ IEEE Std 145-2013, Standard Definitions of Terms for Antennas
2. ^ Cheng, David K. (1992). Field and Wave Electromagnetics, 2nd Ed. Addison-Wesley. p. 635.