suitable frequencies and strengths to be transmitted over great distances by reflection from the ionosphere or from aircraft or spacecraft. Illumination of other spacecraft or aircraft by the beam of the SPS may result in similar effects. These vehicles carry antennas connected to nonlinear receiving and transmitting circuits. Especially in the transmitting circuit, the SPS frequency and the other transmitting frequency, or their harmonics, may mix in ways to produce strong out-of-band radiation. Nonlinear effects from metal structures on the vehicle may also be expected. Accurate prediction of the effects discussed here is likely to prove difficult. However, as they have the potential to pollute nearly the entire radio spectrum within a substantial geographical area centered on each rectenna, it is essential that they be studied carefully. INTERFERENCE REJECTION PROPERTIES PECULIAR TO SYNTHESIS ARRAYS (AS THE VLA) Calculations have been made to estimate the quantitative effects of the fringe-frequency averaging and the decorrelation on the VLA sensitivity to interference. Other synthesis arrays exhibit qualitatively similar effects whose magnitude depends on parameters of the particular array. The fringefrequency averaging depends on the size of the synthesized field of view and hence on the configuration and observing frequency. The most compact VLA configuration, for which the interference reduction is least effective, will be used as an example in considering the tolerable interference levels. For this case the reduction is approximately 10 dB for the 18 to 21-cm band and 17 dB for 1.3 cm. These figures refer to declinations south of +70°, and the fringefrequency averaging becomes less effective toward the pole. The decorrelation effect depends mainly on the antenna configuration and the bandwidth, and again the most compact configuration will be considered. The interference reduction is approximately 14 dB for a 25-MHz bandwidth and 17 dB for a 50-MHz bandwidth. These figures apply to a source of interference at the declination of the satellite, -5.5°, and for an observing declination north of +20°. As the observing declination approaches that of the satellite, the interference reduction becomes much less effective.
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