5. 0 INTEGRATION OF IMPROVED DIODES AND CIRCUITS INTO A DESIGN COMPATIBLE WITH THE LONGER RANGE OBJECTIVE OF A LOW-COST RECTENNA SUITABLE FOR SSPS DEPLOYMENT 5. 1 Introduction Prior to this contract, there had already been an appreciable base established for a low-cost design. Early rectenna designs had employed a two- plane construction in which one plane was merely a metallic reflector of some kind while the other plane contained the half wave dipole, the rectification circuit, and the DC collecting busses. However, in an attempt to better understand the behavior of the rectenna array, as well as to incorporate some necessary harmonic filtering into the system, the development had subsequently gone in the direction of a three-plane system in which the DC power was collected in a third plane which was behind the reflecting plane. This development sponsored by MSFC support led to better performing rectenna hardware as well as to a better understanding of its behavior. It was then very logical to use the design of the MSFC hardware as a base for fulfilling the NASA sponsored JPL contract calling for the efficient reception and rectification of substantial amounts of microwave power (3 0 kw) that was to be transmitted over a distance of approximately 1.6 kilometers. At the successful conclusion of that effort it was logical to think in terms of returning to the two-plane construction and to incorporate the best features of the three-plane rectenna development into it. The present study has successfully pursued this conversion while taking these pertinent factors into account: (1) the need for protecting the active portion of the rectenna from the weather environment (2) the need to minimize radiation of unwanted harmonics (3) the desire to utilize the front active plane of the structure as a structural element to reduce the cost of materials and the cost of fabrication, and (4) the need to develop an output voltage of at least 1000 volts to establish efficient DC to 60 cycle inversion. It is believed that the design approach that has resulted from the present contract fulfills all of those requirements as well as lending itself to a low-cost high speed construction. There are many details, of course, that need to be filled in. The general design approach that has resulted from this study is shown in Figures 5-1 and 5-2. The construction shown in Figure 5-2 is identical to that tested out in the 199 element array for compatibility evaluation except for the addition of the teflon caps over the half wave dipoles and the replacement of the solid metallic reflector with the electrically equivalent wire mesh. The exploded view of the foreplane structure shown in Figure 5-3 clearly differentiates between the basic core structure and the external metal shield which also doubles as a major structural element. In the material that follows we will discuss various aspects of the development and how it should integrate into further development programs and the final manufacturing process for the SSPS. The description of the testing and electrical data are given in Sections 5.5, 5. 6, and 5.7.
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