Fig. 9. Subarray test site panel mounted at the end of the antenna range. The total microwave test project would provide quantitative data on critical parameters such as: Transmission/receiving efficiency rf-to-DC conversion efficiency Beam forming and steering accuracy Thermal control characteristics Mechanical alignment and tolerance effects Component failure effects Radiofrequency-interference (RFI) characteristics Such a project is considered a critical element of a continuing Solar Power Satellite exploratory research program. The microwave beam environmental concerns are in three areas, (13-15): (1) interference with RF communications, (2) interaction with the ionosphere, and (3) biological effects on life forms near the ground-based receiver. The RFI effects due to spurious noise of the space transmitter amplifier tubes are expected to be held below current requirements by the use of phase-lock loops and multiple-cavity filters. A significant development and test program will be necessary to confirm that candidate elements of the satellite RF system meet the RFI requirements. The microwave beam/ionospheric interactions depend on the microwave beam intensity, its frequency, the altitude, (D, E, or F regions of the ionosphere), and the angle between the beam and the Earth's magnetic field lines. At some threshold power density level, nonlinear interactions between the power beam and the iono-
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