What is antenna radiation efficiency?
Radiation efficiency is the ratio of the total power radiated by an antenna to the net power accepted at its terminals; for a series model it is ecd = Rr/(Rr+RL), where RL is conductor and dielectric loss resistance.[1][2] Total efficiency also includes reflection loss: e0 = er·ec·ed = (1−|Γ|²)ecd.[2]
Where does antenna loss come from?
- Conductor loss: finite conductivity and skin effect; dominant in small loops and meanders.
- Dielectric loss: loss tangent of substrates, ceramics and plastics near the antenna.
- Matching-network loss: finite Q of inductors and capacitors.
- Coupled lossy objects: hands, heads, batteries, display panels.
Why are small antennas inefficient?
The radiation resistance of an electrically small dipole falls as (l/λ)² and that of a small loop as (C/λ)⁴, so even a fraction of an ohm of loss resistance produces large loss.[2] A single-turn loop 1 m in diameter at 3.5 MHz has Rr well under one milliohm, which is why HF magnetic loops use thick copper and vacuum capacitors.[3]
How is efficiency measured?
Methods include gain/directivity comparison (G/D from 3D patterns), the Wheeler cap method, which compares input resistance with and without a conducting enclosure around a small antenna, reverberation chambers, and total radiated power integration in an OTA chamber.[4][5]
What efficiencies are typical?
Well-designed dipoles, horns and reflectors exceed 90%. Patches on low-loss laminates are often 80–95%; on FR-4 noticeably less. Embedded antennas in phones and IoT devices commonly range from about 20% to 70% depending on volume, band and user loading.[6]
Frequently asked questions
What is the difference between radiation and total efficiency?
Radiation efficiency excludes mismatch; total efficiency multiplies it by 1−|Γ|².
What is −3 dB efficiency?
50%: half the accepted power is radiated.
Can efficiency exceed 100%?
No; measured values above 100% indicate measurement error.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “IEEE Standard for Definitions of Terms for Antennas (IEEE Std 145-2013)”. IEEE Antennas and Propagation Society. 2014.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “The ARRL Antenna Book for Radio Communications”. ARRL. multiple editions.
- “The Radiansphere Around a Small Antenna”. H. A. Wheeler, Proceedings of the IRE, vol. 47, no. 8, pp. 1325-1331. August 1959.
- “IEEE Recommended Practice for Antenna Measurements (IEEE Std 149-2021)”. IEEE Antennas and Propagation Society. 2022.
- “Modern Small Antennas”. K. Fujimoto and H. Morishita, Cambridge University Press. 2013.