radiating element. The second level consists of a phase conjugation system which receives a uniquely-designed pilot signal allowing reconstruction of a phantom carrier at the same frequency as the power beam, thus avoiding problems of squint due to frequency offsets between the pilot and power beam signals. The pilot signal design also provides for anti-jamming (security) of the pilot receivers, provides additional processing for isolation of the pilot receiver from the power signal, and allows for multiaccess operation (i.e., more than one SPS can be intercepted by the same pilot signal without interference). The third level of control is associated with maintaining an equal and constant phase shift through the microwave power amplifier devices. In addition, this concept of phase locking around the power amplifiers will provide added suppression of transmitted noise and reduce the SPS RFI (radio frequency interference) potential. As part of the preliminary analysis and system definition activity, an SPS microwave system computer model has been under development which will provide a flexible system engineering tool for evaluation of SPS microwave system performance as parameters which uniquely affect the phase control system are varied. Efforts thus far have concentrated on modeling and performance trades associated with the reference phase distribution tree. Tentative results show that beam pointing is most sensitive to errors in the first few branches of the distribution tree, while errors in the later branches reduce main beam gain and spread the radiation pattern. These results will be used to continue definition of the reference phase control system. Rectenna Configuration - As mentioned in Section 3 on microwave system efficiencies, some of the earliest efforts on the SPS were directed toward studies and experiments to improve the power collection and conversion efficiencies. Raytheon pioneered these early efforts and essentially verified the rectenna concept (ref. 20,23,24). The initial studies reviewed several options for the antenna design at the receiving site, including contiguous horns, contiguous reflectors, phased array of small aperture elements with
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