approximately 56 percent. It can be seen that only the rectenna elements at the center of the rectenna receive enough incident radiation to provide a relatively high DC/RF conversion efficiency. There are several ways to improve this condition. a. The rectenna could be made larger to collect more incident radiation. This approach does not appear to be good because the power density levels drop off fairly rapidly for radii above 5 KM. b. Investigate the use of an array of dipole antennas which would collect enough RF power to feed into a single diode--enough to operate on the high end of the diode efficiency curve. c. Undertake development of a rectenna element with higher efficiencies at low power density levels. Items b. and c.» above should be studied further and will be discussed in somewhat more detail in the section on "Technology Status, Criticality."
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