How do the atmosphere and rain attenuate radio waves?

Above roughly 10 GHz, atmospheric gases and rain add significant loss to free-space path loss. Water vapor has an absorption line at 22.235 GHz and oxygen a strong complex of lines near 60 GHz, where sea-level attenuation reaches roughly 15 dB/km; ITU-R P.676 provides the calculation method.^[1] Rain specific attenuation follows γR = k·Rα dB/km, with frequency- and polarization-dependent coefficients k and α tabulated in ITU-R P.838.^[2]

Why is 60 GHz useful despite oxygen loss?

High absorption limits range and interference, enabling dense frequency reuse for short-range links (e.g., IEEE 802.11ad/ay) and inter-satellite links where there is no atmosphere. Unlicensed 57–71 GHz operation is permitted in the US under Part 15.255.^[3]

How is rain fade predicted?

Compute γ_R from the rain rate exceeded for the target percentage of time (e.g., 0.01% of a year from ITU-R P.837 maps), multiply by an effective path length (ITU-R P.530 terrestrial or P.618 Earth-space procedures), and add to the budget. Ka-band satellite links in tropical climates can require margins of tens of dB for high availability.^[2]

What other effects matter?

Clouds and fog (ITU-R P.840), scintillation, tropospheric refraction (ducting, k-factor), and ionospheric effects at lower frequencies (Faraday rotation, scintillation, absorption at HF).

Frequently asked questions

See also

• Free-space path loss
• Link budget
• Frequency bands
• Path loss models

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

1. “Recommendation ITU-R P.676: Attenuation by atmospheric gases and related effects”. ITU-R. current version.
2. “Recommendation ITU-R P.838: Specific attenuation model for rain for use in prediction methods”. ITU-R. current version.
3. “47 CFR Part 15: Radio Frequency Devices”. U.S. Federal Communications Commission, via eCFR. current.