EXECUTIVE SUMMARY It is necessary for the EMC analysis of the SPS to know microwave field strengths that would be expected inside various structures, particularly buildings and vehicles. Theoretically, such structures could concentrate incident microwave energy to produce fields more intense than would otherwise be expected. Very little work has been done explicitly on this problem, but a substantial body of theoretical and experimental information is available on the coupling of microwaves into enclosures and their behavior therein. An exact, detailed analysis of the microwave properties of habitable structures is not practical due to the tremendous variety of materials and complex geometries involved. The problem of estimating the fields inside habitable structures exposed to microwaves near an SPS rectenna is analyzed in this report, with particular attention to the possibility of increases in field strength. This study describes and discusses relevant physical processes, lists measured values for many of the quantities involved, and cites actual microwave field strengths measured inside houses exposed to 2.6 GHz radiation from a satellite. Key results are summarized below. To determine microwave field strengths inside a structure, the coupling of energy into the structure and its behavior inside, including reflections (possibly resonant), must be understood. Coupling to the interior could occur via relatively microwave-transparent openings (windows, for example) or through wall materials, which in general do not transmit microwaves as well. The following approximate microwave transmissions for representative structural elements have been measured: Metal walls or screening, or even foil, transmits very little 2.45-GHz microwave energy (less than 1%) if openings or joints are substantially less than an inch long. Structure % Transmission Dry Wet Wooden Wall 15 6 Frame Wall 40 15 Window (wood sash) 70 40
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