System performance would be impacted in varying degrees by operation at these higher frequencies, increased atmosphere attenuation, and scatter and refractive anomaly sensitivity. General expotential relationships prevail, with absorption windows available at discrete frequencies above 30 GHz. For the power ranges required for SPS, equipment development and operational uncertainties for the regions above 20 GHz presently are fundamental constraints. Planning for future operation at the higher end of this region would be dictated by the current system developments for the 10 GHz to 20 GHz region. The general allocation and assignment density in relation to the higher microwave spectral regions is shown in Fig. 4.3. One possible advantage to operation above 25-30 GHz is the probable efficiency and emission improvements attendant upon use of the gyrotron power amplifier. For these higher frequencies, the system components would be physically smaller for parameters identical with 2.45 GHz operation (antenna array, rectenna). Control and operational stability problems would, however, be aggravated because of the increased atmospheric interactions. Higher frequencies would also reduce the possible ionosphere beam distortion and parametric modification effects. Heating and dynamic perturbations would be negligible at frequencies higher than 30 GHz. Lower frequencies cannot be considered because of the increased victim system densities within the continental United States. The increased Fig. 4.3. General Spectrum Assignment Densities
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