Sun Tracker Measurements of Attenuation by Rain at 16 and 30 GHz

The advent of high performance booster rockets makes it possible to put very high-capacity microwave repeaters in synchronous orbit, possibly resulting in low cost per channel.1 The large bandwidth required for such a system is in direct conflict with the crowded condition of the microwave spectrum below 10 GHz. We must therefore consider the possibility of operating such a system at frequencies above 10 GHz and must assess the magnitude of large attenuations which may be caused by heavy rain. Estimates based on attenuations for surface rainfall conditions2 and models of the structure of rain storms indicate that such a system is feasible,3 but direct measurement of the attenuation statistics is necessary.* * The overall plan for a system calls for ground-station space diversity, but that is not discussed here. 1383 1384 TI-IE B E L L SYSTEM TECHNICAL JOURNAL, M A Y - J U N E 1969 The apparatus described in this paper has been set up at Crawford Hill, Holmdel, New Jersey, to measure the attenuation statistics of an earth-space path at 16 and 30 GHz using the sun as a signal source. At night the same equipment monitors the temperature of the antenna with the beam in the local meridian. Attenuations up to about 10 dB can be deduced from these temperatures. Attenuations of greater than 30 dB can be measured in the sun-tracking mode; the output time constant is two seconds so that even relatively fast fades can be followed.! Daily cycling of the equipment is automatic and sun coordinates are stored for a week's unattended operation.