The Effect of Variation in Atmospheric Absorption on Millimetric, Terrestrial, Telecommunications Links

When planning the link budget for millimetre and sub-millimetre wave telecommunications links, the attenuation by atmospheric gasses is taken into account. However, at millimetric frequencies above 50 GHz, it may become necessary to account for the temporal variations in absorption when calculating fade margins. Attenuation due to atmospheric absorption varies with temperature, barometric pressure and humidity, and the amplitude of variation can become significant compared to rain fade margins. This paper examines the variation in absorption between 10 and 1000 GHz derived from meteorological time-series. This variation is compared to the attenuation time-series experienced by two experimental, 5 km links operating at 54.5 and 56.5 GHz in the southern UK. A method is developed to predict the average annual distribution of specific attenuation due to atmospheric absorption, based on easily obtainable meteorological parameters. A further method is developed to integrate this variation into existing models of annual fade distribution and these results are compared to measured distributions.