be reduced as well. This may be achievable using solid state electronics. In the last ten years we have seen development of microwave integrated circuits, thin-film transistors, and thin film microwave rectennas. Since solid-state electronics has developed considerably, it is now reasonable to consider using them instead of tubes as the microwave source for a SPS. Tubes are well developed, and have been the DC to RF converter of choice for most high power applications. However, use of microwave tubes requires the electrical power to be collected from the photovoltaic array on the SPS and distributed to them, and their waste thermal energy transported away. A distributed solid state network of DC to RF devices operating at much lower power densities could greatly reduce or eliminate these supporting power and thermal transport subsystems. Microwave rectifying antennas (rectennas) for receiving microwave power and converting it to DC power have been demonstrated using thin-film techniques on a thin plastic substrate [13]. Using such a technology as a microwave source requires replacement of the rectenna GaAs diodes by appropriately phased solid-state microwave generators. Similar solid state devices and phased arrays are being developed for communication and radar applications, e.g., conformal antennas on aircraft skins, drivers for large aperture radars, space communications phased arrays. An extension of this type of phased array closely couples the distributed power source, i.e., solar cells, with the RF generator and antenna. Such a concept for integration of the solar cell with the microwave oscillator and antenna is shown schematically in Figure 2. A slightly more complex version, where the solar cell metalization could possibly be used for the antenna in a “push-pull” configuration, is shown conceptually in Figure 3. What is created is a self powered RF transmitter that converts sunlight in to RF out. For the SPS design being discussed the output beam is received for power. It could just as well be for communications, radar or other uses e.g. a self powered RF repeater. These uses will not be addressed in this paper.
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