POSSIBLE OVERLOAD AND PHYSICAL DAMAGE OF A RADIO ASTRONOMY RECEIVER CAUSED BY THE SPS H. Hvatum The extremely high microwave power radiated from the SPS (several orders of magnitude higher than any other existing or planned microwave transmitter) raises the question of overload problems and, perhaps, physical damage to radio astronomy receivers. It is therefore of interest to estimate the power levels in a radio astronomy receiver under various conditions that might arise. One may safely assume that the main beam of the SPS will always be directed towards a rectenna and that in case of equipment failure the beam will degenerate into the phase failure mode. Thus, a radio astronomy receiver will never be exposed to a SPS main beam, but will be illuminated either by the SPS side lobe structure or the phase failure mode radiation. If one assumes that a complete SPS consists of approximately 100 SPS sets (60 and 120 sets have been mentioned), the average distance between two adjacent rectennas will be about 300 km. Thus, a radio astronomy installation will, on the average, be within a few hundred kilometers from a rectenna and be illuminated with about 3 mW/m from one SPS transmitter. With 100 systems in operation, the flux will be higher, although not 100 times higher since the contribution from most systems will come from far-out side lobes. A combined flux of 50 to 100 mW/m seems to be a reasonable estimate of the combined power flux that could be expected from all SPS transmitters. With 1 OlO SPS transmitters in simultaneous operation, it becomes quite likely that a grating lobe with a power flux of 100 mW/m will fall on a radio astronomy telescope. In the following calculations, 100 mW/m has been used as a typical expected power flux at a radio astronomy observatory. The interfering radiation will be coupled into the radio astronomy receivers either through the side lobes of the radio telescope or occasionally through the main beam. Both cases must be considered.
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