transmitting antennas, the radiation pattern will be a far-field pattern, essentially, exponentially tapered at the receiver, while for larger antennas the pattern will be that of the Fresnel zone or near-field. Here, too, with proper phasing, it appears to be possible to receive 80% of the transmitted power with equal antenna diameters. The most obvious differences between the two figures is that in the SMART design, the module power remains constant at 2.2 W and the substrate temperature is 47.5°C. The receiving antenna diameter remains about the same as that in the Goubau design because the same limitation of 23 mW/cm2 peak power density is kept. The transmitting antenna diameter, however, increases with increasing system power. The solar cell array area is about the same because the overall efficiency has not changed much. The major disadvantage of the SMART system is that it requires mirrors of large size to illuminate the solar side of the modules which must rotate as the satellite orbits the earth. We believe, however, that there is enough merit in the proposal to warrant further study. Acknowledgments — The author is indebted to his colleagues at the Microwave Technology Center of the RCA Laboratories and to Mr. Lou Leopold of NASA Johnson Space Center for their help and encouragement. This work was supported in part under Contract NAS9-15755 awarded to RCA Laboratories by NA- SA/JSC. REFERENCES 1. G. Goubau, Microwave Power Transmission from an Orbiting Solar Power Station, J. Microwave Power, 5(4), 1970. 2. F. Sterzer, Large Active Satellite Antennas Based on Solar-Microwave Array Technology (SMART), Digest of National Radio Science Meeting, Bioelectromagnetics Symposium, June 18-22, p. 143, 1979. APPENDIX A. LIST OF EFFICIENCY SYMBOLS re = Solar cell conversion efficiency ri,t = microwave transmitter distribution efficiency = microwave conversion efficiency (de to rf) r),, = transmission efficiency (transmitting antenna to receiving antenna) r)e = conversion efficiency (rf to system power)
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