SECTION 9 RECEIVING ANTENNA The collection and rectification of microwave power from space is conceptually a two step process and in the early stages of development of microwave power transmission it was treated in this fashion. However, it was determined early that the individual requirements placed upon the collection of microwave power and upon the rectification of microwave power in a two step process could not be met by any available technology or any forseeable technology development. The rectenna concept, however, which in effect combined collection and rectification into a one-step process was found to meet all of the requirements for the collection and rectification of the power in a free-space microwave beam. Furthermore, it was found that the concept could be experimentally established immediately from available components and technology. It is also of interest to note that the portion of a microwave power transmission system represented by the collection and rectification of microwave power has grown in the last decade from the weakest and most insecure portion of the of the system to the strongest and most secure. This has come about not only because of the soundness of the rectenna concept but also because this is the portion of the system whose development has received the mo$t attention. The most recent portion of this development process has considered not only the efficiency and reliability aspects, but also those aspects dealing with low-cost fabrication. This has resulted in a large amount of ’Winnowing" of design approaches to arrive at a rather high level of design specificity. Since much of this winnowing has occurred in the period of the last three years, it is not highly documented although the general direction and the motivational influences are recorded in Reference 1. Therefore, it is desirable initially to review some of the factors which have led to the present detailed design. 9. 1 MICROWAVE RECTIFIER TECHNOLOGY The efficient conversion of microwave power directly into dc power is a technology that is specifically related to the concept of power transmission by microwaves in either a free-space or confined waveguide mode. As contrasted to dc to microwave conversion which has received broad support from many areas, there has been little support of the reverse process.
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