also increase with a corresponding reduction in rectenna size. Since land sites for 10-kilometer diameter rectennas are limited, smaller rectennas are considered particularly advantageous. The results indicate the rectenna size decreases until /0 reaches approximately 40 mW/cm2, after which the size remains constant. As the antenna thermal limit is raised as shown in Fig. 7, the optimal antenna size decreases and the rectenna increases. The trade-off of minimizing rectenna size as an environmental consideration versus the cost advantage of higher antenna thermal limits remains an open issue. OPTIMIZED SYSTEM CONFIGURATIONS It is possible to define optimized antenna systems as functions of specific ionospheric, thermal, and sidelobe constraints. Representative optimized systems for selected constraint combinations are shown in Fig. 8. Each of these systems has a cost advantage over the 10 dB Gaussian reference system because larger microwave powers are being transmitted. Conclusions from Fig. 8 include the following: [1] Lower sidelobe values (50) require larger transmit antennas; [2] In order to suppress sidelobes, the tapers usually increase near the antenna edge; 13] High ionospheric limits signify larger transmit antennas;
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