What is antenna gain?
Antenna gain is the ratio of the radiation intensity in a given direction to the intensity that would result if the power accepted by the antenna were radiated isotropically; it equals G = ecd·D, where ecd is the radiation efficiency.[1] By the IEEE definition gain excludes impedance-mismatch and polarization losses; realized gain includes mismatch, Gre = (1−|Γ|²)G.[1][2]
What is the difference between dBi and dBd?
dBi is relative to an isotropic radiator; dBd is relative to a lossless half-wave dipole, whose gain is 2.15 dBi. So G(dBi) = G(dBd) + 2.15.[2] Regulatory and amateur literature sometimes uses ERP (dipole reference) rather than EIRP; see EIRP and ERP.
What are partial gain and realized gain?
Partial gain is the gain for a specified polarization component, so total gain is the sum of the co- and cross-polar partial gains.[1] Realized gain multiplies gain by the mismatch factor 1−|Γ|², which is what a system actually experiences; a 2:1 VSWR reduces realized gain by 0.51 dB.
How is gain measured?
The most common method is gain transfer (substitution): compare the received power from the antenna under test with that from a standard gain horn of known gain. The three-antenna method uses three unknown antennas and three Friis measurements to solve for all gains without a reference.[3] See gain measurement.
Does higher gain always mean better?
No. Gain is redistribution: more gain in one direction means narrower beamwidth and less coverage elsewhere. Mobile devices often prefer low-gain, near-omnidirectional antennas; point-to-point links prefer high gain. Regulations may limit gain or EIRP.[4]
Frequently asked questions
What is the gain of a half-wave dipole?
About 2.15 dBi if lossless; real dipoles are typically within a few tenths of a dB.
Can antenna gain be negative?
Yes; small, inefficient antennas often have peak gain below 0 dBi.
Does gain include cable loss?
No; cable loss is a separate term in the link budget.
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.
- “IEEE Recommended Practice for Antenna Measurements (IEEE Std 149-2021)”. IEEE Antennas and Propagation Society. 2022.
- “47 CFR 15.247 — Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz”. U.S. FCC, eCFR. current text.