sible for great improvements in all parts of the technology, but particularly in rectenna technology. Ultimately, all the advancements were put together in a demonstration of overall DC to DC efficiency of 48% in 1964. In 1965, the overall efficiency was raised to 54% and certified by the Quality Control Department of JPL at Raytheon. In this latter demonstration, the microwave generator efficiency was measured at 69%, the transmitted beam efficiency at 95%, and the rectenna overall capture and rectification efficiency at 82%. Power levels were modest. About 600 watts was obtained from the rectenna [6] (Fig. 2). This demonstration at Raytheon and certification by JPL was essential to the acceptance of the technology by the scientific and engineering communities. For example, the antenna community is accustomed to capture efficiencies of uniformly illuminated apertures of not more than 80%. By adding the rectification function to each individual dipole antenna in the array, however, its capture efficiency increases to 100%. The array also becomes desirably non-directive and its overall capture and rectification efficiency is typically over 80% where most of the inefficiency is caused by diodes and skin losses in the rectifier. It is quite likely that this well documented demonstration [6] and the well documented technology developments that were associated with the components going into the demonstration [7] will never be repeated. However it is interesting that with the best of today's technology, it should be possible to achieve an overall DC to DC efficiency of approximately 70% if it were repeated. Demonstration of Transmission of Significant Amounts of Power over Significant Distances Following a briefing on the SPS circa 1970 by Dr Peter Glaser and others to a
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