The life test that was run is important because it was the first and only life test that has been run on Schottky barrier diodes used as high power microwave rectifiers. Normally these devices are used in Impatt applications. It was appreciated that the dissipation level in the Schottky barrier diode when used as a microwave rectifier would be considerably below the dissipation level when it is used as an Impatt device and that the de bias on the diode would be less than half that in an Impatt device. These were factors which would normally enhance the life of the device. Still the microwave power rectification was a new application for the device and there had been no life experience. Fortunately the rectenna designed as part of a complete microwave power transmission system (shown in Figure 1-13) for Marshall Space Flight Center made a natural test rack and panel for the evaluation of diodes used in RXCV rectenna elements. 199 rectenna elements could be inserted into the rectenna test panel. These elements were the same ones used in the certified demonstration illustrated in Figure 1-13. Further, the radial Gaussian pattern of illumination made it possible to vary the operating power level of the diodes over a wide range and provide a step stress kind of life test. The rectenna elements were combined into sets, each set being comprised of those elements which had a common radius from the center and therefore similar power illumination as indicated in Figure 5-13. The de output terminals of all the rectenna elements in a set were connected in parallel across a common load for that set. If only one diode shorted out, there would be zero voltage across the load which would extinguish a light normally continuously on. In the case of an open diode, a reduction in power output of the set would be found when the total current in a set was periodically checked. It was convenient to break the total number of elements down into seven groups depending upon the incident power. The power level and set numbers included in a group is given below. It is therefore seen that the life test is conducted with a power range of over 20, making it possible to observe if the diodes in the high power range degrade more rapidly than those in the low power range. Using this equipment a life test was started on 17 March 1975 and with occasional interruptions had reached 2913 hours by 22 Sept. 1975. During
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