B.S.T.J Briefs: The Effect of Rain on Circular Polarization at 18 GHz

Synchronous satellite service for Alaska, and possibly other places, requires that ground station antennas point at low elevation angles. For example, from Point Barrow (71°N, 155°W), such a satellite would never be more than 11 degrees above the horizon, and for satellite longitudes 45 degrees east or west of Point Barrow, the elevation is only 5 degrees. At such low angles, the attenuation of a nominally clear atmosphere is significant in the 18- and 30-GHz bands of proposed domestic satellite systems. There are also satellite bands near 13 GHz, where the attenuation is expected to be somewhat lower. Predictions of this attenuation have been made,1 but as a check direct measurements have been obtained with the Crawford Hill Sun Tracker as reported below.