2. 0 IMPROVEMENTS IN TECHNIQUES FOR MEASURING THE EFFICIENCY AND LOSSES OF RECTENNA ELEMENTS; MATHEMATICAL MODELING AND COMPUTER SIMULATION OF THE RXCV RECTENNA ELEMENT 2. 1 Introduction As indicated in Section 1. 0, there have been many improvements in the rectenna over a period of time. One of the major improvements has been in the overall efficiency of the rectenna. The overall efficiency is the product of the absorption or collection efficiency and the conversion efficiency. Since it is known that the absorption efficiency is theoretically 100% and that this has been closely approached experimentally, the concern with respect to efficiency is now centered upon the conversion efficiency which is a property of the rectenna element. Improvements in conversion efficiency of the rectenna element through circuit and diode improvements have been an important part of the current technology development contract. As incremental improvements in the efficiency of the rectenna element have become smaller, and as further techniques for improving the efficiency have become less obvious, the need has arisen for more refined measurements. The need exists for increased sensitivity of the measurements, for greater confidence in the data from which the efficiency figures are computed, and for better repeatability of measurements over an extended period of time. The need also exists for a more accurate breakdown of where the losses are occurring in the structure. There is also the need for a tool with which to examine the current and voltage waveforms within this highly non-linear device in great detail - not only to suggest improvements in efficiency but also to anticipate failure mechanisms to which the waveforms could contribute. This may best be done by means of computer simulation. A great deal of progress has been achieved in all of these areas during this technology development program. Much better quantitative data has been obtained in the division between circuit losses and diode losses in the rectenna elements. This data is in the form of both experimental and computer simulation data. In general, there is good agreement between the two kinds of data. The availability of this loss data has made it possible to prepare a balance sheet between the microwave power going into the system and the DC power and the losses coming out of the system. A good balance between the input and the output power and loss measurements, together with an estimate of the error involved in each of the detailed measurements involved, leads to a better confidence in the rectenna element efficiency. The successful mathematical model and computer simulation program resulting from this study is potentially a tool of great importance. Although used with some effectiveness in this study, its application was limited because of a substantial cost involved in applying it more broadly and because of the greater priority of other items within the contract.
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