Attnospheric Absorption

Attnospheric Absorption

An additional loss between the transmitting and receiving antennas is atmospheric
absorption. Water vapor and oxygen contribute most to attenuation. A peak attenuation
occurs in the vicinity of 22 GHz due to water vapor. At frequencies below
15 GHz, the attenuation is less. The presence of oxygen results in an absorption
peak in the vicinity of 60 GHz but contributes less at frequencies below 30 GHz.
Rain and fog (suspended water droplets) cause scattering of radio waves that
results in attenuation. This can be a major cause of signal loss. Thus, in areas of significant
precipitation, either path lengths have to be kept short or lower-frequency
bands should be used.