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, A_e 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.