Under normal operation the radiation from the SPS transmitter will couple into the side lobes of the radio telescope. The side lobe response of a radio astronomy telescope is independent of its size, about 7 dB below the isotropic response. The SPS satellites will be in geosynchronous orbits, which means that they will occupy a band across the United States near the celestial equator, a region of great interest to radio astronomy. One must assume that the main beam of a radio telescope accidentally may point at one of the SPS transmitters. For a 25-m-diameter telescope the gain is about 54 dB at 2.4 GHz, which gives about 61 dB higher power level in the input amplifier compared to the case where the antenna is pointed away from the satellite. In the case of an SPS transmitter operating in the phase failure mode, the radiated beam becomes very wide and will cover the entire United States. The power flux from one SPS will then be 30 mW/m anywhere. A typical radio astronomy system uses parametric amplifiers as low-noise input stages. The overload level, defined here as a 0.1-dB compression in -9 the amplifier, is about 3 x 10 W and the level where the varactor may be physically damaged (burn-out) is about 100 mW. In order to achieve the best possible system noise temperature, a normal radio astronomy receiving system does not employ filters in front of the input amplifer. Thus, a system operating in the 2690 to 2700 MHz radio astronomy band will also be exposed to fields at 2450 MHz, the SPS frequency. The rectennas will reradiate 5% of the incoming power, or about 100 MW. Most of the reradiated power will be at 2.45 GHz, but some (-25 dB) will occur at 4.9 GHz. If one assumes that the reradiation will be isotropic, at a dis- tance of 150 km the power flux will then be approximately 5pW/m . One can now assume the following parameters for the SPS-radio astronomy system:
RkJQdWJsaXNoZXIy MTU5NjU0Mg==