6.0 SUMMARY OF RESULTS The technology development covered by this final report was concerned with improvements in the reception and rectification of microwave power at the receiving terminal of a free-space power transmission system. More specifically, it was concerned with an application to the solar power satellite concept in which solar energy is captured in a geosynchronous satellite and then, after an imtermediate energy conversion process, transmitted to earth by a microwave beam. The background of previous effort in developing a suitable technological approach to this portion of the transmission system,together with system studies which have developed a set of specific requirements, indicated that development be carried forward in certain key areas with the following objectives: 1. More efficient operation in general, but particularly at lower incident microwave power densities. 2. Better confidence and finer resolution in efficiency measurements. 3. Better knowledge of the efficiency loss mechanisms. 4, Better understanding of the operation of the device through computer simulation. 5. Development of improved diodes. 6. A decrease in the radiation of harmonic energy. 7. The development of a design that is environmentally sound. 8. The development of a design that allows low cost production. 9. An assessment of life of rectenna elements. These objectives were addressed in the technology development contract and significant progress was made in all of the areas. The results are discussed in the following material in the same sequence. Items 7 and 8 because of their close overlap are reported upon as a single item. 1. Improvements in Efficiency Improvements in efficiency were accomplished through the use of higher impedance microwave circuits, higher DC load resistances, and the use of improved diodes developed under this study. These were changes incorporated into the rectenna element which is the basic building block of the rectenna. The improvements in efficiency ranged from a fraction of a percent at six to eight watt level of microwave power input to the rectenna element to twenty percent at an input level of 50 milliwatts. More specifically, the changes resulted
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