What is the Impact of the Atmosphere on RF Signal Propagation?

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Raghav Kapur - everything RF

Aug 17, 2017

As we go higher up in frequency, the earths atmosphere starts to impact the propagation of RF signals. RF signals travelling in free space are effected by atmospheric attenuation. This attenuation in the atmosphere is caused mainly by signal absorption by gasses such as O2 and H2O. The effect of signal absorption under 10 GHz is fairly low and predictable, however as we go higher in frequency (specially in to the mm-Wave range i.e 30 to 300 GHz) this attenuation increases significantly, specially at certain frequencies. The attenuation is not only increases but also becomes more dependent on the absorbing characteristics of H2O, O2 and other gasses.

This chart shows attenuation of signals in our Atmosphere by O2 and H2O

As can be seen in the chart above, the attenuation is maximum in a few frequency bands, mainly those of oxygen at 60 GHz and water vapor at 24 GHz and 184 GHz. There are a number of frequency windows where atmospheric attenuation is significantly lower. It is in these gaps where most applications in the mm-Wave frequency bands operate.