1 .0 INTRODUCTION The RF to DC Collector/ Converter technology development with which this report is concerned is in support of the larger technological development of free space power transmission by means of a microwave beam. The efficient free- space transportation of energy by electromagnetic beam brings a new three- dimensional aspect to the transfer of electrical power and permits the coupling of terrestrial power transmission systems to power sources and sinks located in the earth’s atmosphere and space. This report relates to the application of free space power transmission in which the sun’s energy is captured in equatorial geosynchronous orbit, converted to electrical power, and then sent to Earth by means of a microwave beam. At the earth’s surface the microwave power is efficiently collected and converted back into DC electrical power. Improvements in the performance of this receiving system and its reduction to a practical design are the specific subject matter of this report. To place the work to be reported upon in proper perspective, it is desirable to define and review the technology of free-space power transmission with particular emphasis upon prior RF to DC collector/converter technology. 1. 1 Description of free-space power transmission by microwave beam and its early development. Free-space power transmission by microwave beam is defined as the efficient point-to-point transfer of energy through free space by a highly collimated microwave beam. As a technology H) it includes the interchanging of de and microwave power at the transmitting and receiving ends of the system. Free- space is defined to exclude the use of any physically injected material such as waveguides or reflectors between the transmitting and receiving points of the system but not to exclude the presence of gaseous, liquid, or congealed material that exists naturally in the earth’s atmosphere. Free-space power transmission as a technology is differentiated from the use of microwaves in free space for point to point communication purposes by its very high efficiency and by the magnitude of the power which is handled at the receiving point - being in many cases over 90 percent of the microwave power launched at the transmitting point. The efficient collection and conversion of this incoming microwave power to conventional electrical power comprises a unique technology which bears little relationship to the traditional methods of receiving and processing microwave energy in communication and radar applications. The concept of power transfer by radio waves was first pioneered by Tesla (3) at the turn of the century. An acknowledged genius in low-frequency electric power generation and distribution, Tesla became interested in the general concept of resonance and sought to apply this to the transmission of electrical power from one point to another without wires. He built a large "Tesla coil" with which he hoped to produce oscillations of electrical energy around the surface of the earth and set up standing waves into which he could immerse his receiving antennas at the optimum point.
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