What is antenna noise temperature?
Antenna noise temperature TA is the temperature of a resistor that would deliver the same noise power per unit bandwidth as the antenna, kTA; it is the brightness temperature of the surroundings weighted by the antenna pattern, plus noise from antenna losses.[1][2] It sets receiver sensitivity together with the figure of merit G/T in satellite and radio-astronomy systems.[3]
Where does antenna noise come from?
- Cosmic background (≈ 2.7 K) and galactic noise, which dominate below about 1 GHz.
- Atmospheric absorption by oxygen and water vapor, rising toward 22 GHz and 60 GHz bands.
- Ground at roughly 290 K, picked up via sidelobes and back lobes.
- Man-made and atmospheric (lightning) noise at HF.[4]
How do losses add noise?
A lossy antenna or feed of physical temperature Tp and efficiency η yields TA = η·TB + (1−η)Tp. A 0.5 dB loss at 290 K adds about 32 K, significant for a low-noise satellite terminal.[2][5]
What is G/T?
G/T (dB/K) = Grx(dBi) − 10·log10(Tsys), where Tsys = TA + Te,receiver referred to the same point. The downlink carrier-to-noise density is C/N0 = EIRP − Lpath + G/T − 10·log10k, with 10·log10k = −228.6 dBW/K/Hz.[3]
Frequently asked questions
Why do satellite dishes have low sidelobes toward the ground?
To keep 290 K ground noise from raising antenna temperature.
What is Boltzmann’s constant in dB?
−228.6 dBW/(K·Hz).
Does an efficient HF antenna matter for receive?
Often less than expected because external noise dominates the receiver noise.
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.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “Satellite Communications Systems, 5th ed.”. G. Maral and M. Bousquet, Wiley. 2009.
- “Recommendation ITU-R P.372: Radio noise”. ITU-R. current edition.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.