Figure 6.3-1. Structure of Earth's Ionosphere • Above plasma frequency attenuation decreases with increasing RF frequency. For (RF frequency/plasma frequency) ^270, attenuation <10“4 (effect of geomagnetic field is small here). 2 • Therefore, <23 mw/m will be absorbed in ionosphere; this is much less than absorption due to other sources (high power radars, radio and TV stations, etc.). The RF energy absorbed by the ionosphere is a maximum at the ionospheric plasma frequency (^9 x 10^ Hz), decreasing with the square of the ratio of the RF to the plasma frequencies above the plasma frequency. The effects of the geomagnetic field modify this somewhat, but the attenuation of the SPS microwaves will be <10"4. For a maximum power density of 230 w/m^ , this 10~^ attenuation will be small compared with that of high power radars, some radio and TV stations, etc. Individually, high power radars operating at frequencies of the same order of magnitude as the ionospheric plasma frequency can produce the Luxembourg effect—a situation in which sum and difference frequencies for a radio station and the high power radar result when both are interacting with the same portions of the ionosphere. The 230 w/m^ at 2.45 GHz is too little power at too high a frequency to produce or to be seriously affected by the Luxembourg effect. The problem of RF interference (Figure 6.3-2) appears to be more serious. According to the International Radio Regulations (Section 470 NGA) satellite RF radiations between 1.67 and 2.535 GHz must not exceed -168 dBw for any 4-kHz
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