In conclusion it is observed that the balancing procedure just described and used in one example greatly improves confidence in the accuracies of all the measurements. The establishment of probable errors for each of the individual measurements eliminates the possibility of two or more gross measr urement errors offseting each other to provide false confidence. Even greater confidence results from including further results of computer simulation to be described in Section 2.3. In the quest for higher efficiency, it is noted that the diode itself is the greatest source of loss particularly at the lower power levels. The circuit loss at approximately 3% is relatively small and tends to be independent of power level. However, at the lower power levels, it may be found that a circuit which greatly reduces the diode losses may significantly increase the circuit loss. 2. 3 The Development of a Mathematical Model of the Rectenna Element Together with Computer Simulation Program and its Use 2.3.1 Introduction A major feature that characterizes the present standard design of the rectenna elemen t that has been used in the establishment of 54% DC to DC microwave power transmission efficiency and in the successful JPL demonstration of power transmission over a distance of 1.6 km is the use of a single diode shunted across a transmission line and used as a half-wave rectifier. This approach was adopted in 1972 and represented a distinct departure from the full wave bridge rectifier design that had been used up to that time with a high degree of success. A principle reason for the departure was a simultaneous recognition of the need for a better understanding of the functioning of the rectenna element and the difficulty of analyzing the device because of the complexity introduced by its high non-linearity and harmonic contect for the wave forms. Obviously, if an analysis were to be attempted, the initial effort would be made easier by the simpler math model afforded by the half-wave rectifier approach. A substantial start on such a mathematical model and computer simulation program was made by E. E. Eves of Raytheon at that time but the contractual support was not sufficient to finish the work. (9) Meanwhile, many advantages afforded by the rectenna element with a half-wave rectifier had become evident. Acceptable efficiencies were being measured, and it was recognized that for the "power from space" application a single GaAs diode would adequately handle the power requirement placed upon a single rectenna element. With the realization of an apparently efficient and practical rectenna element the role of a computer simulation program has shifted to an exploratory tool for further optimization of the efficiency and to help expose any phenomena that might be a source of trouble at some time in the future but which had thus far not been detected experimentally. It is of interest that one such phenomena seemed to have been uncovered. This will be discussed later in this section. In this connection, it has been generally noted that many subtle problems are encountered in the production of items that were never encountered in their development, simply because the production situation presents a better chance
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