One of the prime objectives of this study was to determine if the dc-dc efficiency goal of 65-70 percent was a potentially achievable number. This efficiency baseline is extremely important since the basic SPS sizing is dependent on this number. The study shows that based on previous study results and Rockwell's data, a 65 percent dc-dc efficiency will be a realistic goal for the MPTS. Thus, this power transmission study was based on a 5-Gw system with a transmitting frequency of 2.45 GHz, 10-dB taper Gaussian distribution with 10 steps, and a maximum operating temperature of 485°K. The subarray baseline size was 10 meters square; however, this size will require further optimization to achieve maximum efficiency in element factor, fabrication, maintenance, and transportation, and mechanical accuracy. Rockwell's total systems design indicated further optimization must be made in determining the optimum tube power level. Figure 2.3-1 shows tube relative costs versus radiators/power amplifier. (This chart was based on the central region of the MW antenna array.) Note that as the power of the amplifier increases, the relative cost of producing power decreases; however, the feed distribution for the array increases in complexity and cost. The crossover of these curves will determine the optimum power level. This tradeoff should be analyzed in detail in future studies. RF noise generation of the SPS tubes will be one of the major tradeoff parameters of klystrons and amplitrons. The magnitude of RF noise and its associated filter requirements also should be considered in future studies. Figure 2.3-1. Conceptual Diagram Showing Array and Amplifier Cost Trends Versus Amplifier Size
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