8.5. White Paper: Richard Dickinson (Paper previously presented at 1996IECEC, Washington, DC) 96575 ISSUES IN MICROWAVE POWER SYSTEMS ENGINEERING Richard M. Dickinson Jet Propulsion Laboratory 4800 Oak Grove Drive. M/S 238-438 Pasadena, California 91109 ABSTRACT The key issues in microwave power system engineering are beam safety, frequency allocation, and affordability. These major issues are presented, discussed, and suggestions for resolving them are offered. Tie issue of beam safety can be captured in the phrase “Fear of Frying.” Can a properly engineered beamed power safety system allay the public perception of microwave radiation dangers? Openness, visibility? and education may be keys to resolving this issue satisfactorily. “Not in my Spectrum” is a phrase that is frequently encountered in connection with the issue of where can the microwave power beam frequency be located. International cooperation may provide a pan of the solution to this issue. “Wow. that much!” is a phrase encountered when dealing with the issue of economic affordability of large beamed power systems. A phased engineering approach for multiple uses even during construction is presented to aid in gamering revenue during the system build phase. Also, dual mode dc-RF converters are encouraged for bi-directional power flow utility and economies of scale in production. INTRODUCTION The continuing evolution of wireless power transmission (WPT) system engineering studies has revealed that certain key issues have staying power. They are beam safety, frequency allocation, and affordability. These are in addition to the usual system engineering issues of choice of circular vs. dual-linear or tracking polarization, sizing of transmitting and receiving apertures, aperture tracking vs. electronic beamsteering, solid state vs. tube, beam coupling efficiency aperture power density taper vs. sidelobe levels, etc. If most systems were non-radiating, wherein the RF fields are confined inside metallic waveguides, there would only be issues of cost and affordability. However, the most useful applications of WPT systems are radiation within and to and from the atmosphere and space. Existing high-power micro wave systems are for communicating with spacecraft, space objects, and aircraft for radar and telecommunications purposes. They are not used for transferring significant levels of electric power, which is the prime focus of this paper. The interfacing of beamed power with the public provides for the points of debate or controversy. People are rightly concerned about potential or perceived harmful effects of microwave radiation. A good system design should feature beam monitoring equipment and fail-safe control techniques that are known, visible, and understood to assure both public and operator safety. Spectrum allocations for the specific purpose of power beaming are a very contentious issue due to the there being no defined service as such and the intense competition for a limited resource. Also, the potential is real for causing harmful interference even out of band if proper engineering is not applied to filtering harmonics and the prevention of potential intermodulation and reradiation. Furthermore, the nature of the Earth’s atmosphere gaseous absorption and meteor scattering when coupled with the laws of diffraction very much constrain the useful frequencies for effective power beaming. Nevertheless, international cooperation with setting priorities for spectrum usage may resolve some of the contention. Economic affordability is a large hurdle for most high-power systems and is especially challenging for wireless power systems. Typical designs produce no revenue until the entire system is assembled. A phased approach yielding multiple uses that could produce revenue during system buildup would be very desirable. Also, if systems could be engineered to require only a few common parts then economies of scale during production could ensue. THE BEAMED POWER SAFETY ISSUE Anything connected to the word radiation is suspect, even though the low frequency beamed power systems that are proposed around S-band are so physically large and the ranges of operation are so far away that the peak RF power densities (20-30 mW/sq. cm) are
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