0191 -9067/82/040281-19$03.00/0 Copyright ® 1983 SUN SAT Energy Council ANTENNA OPTIMIZATION OF SINGLE BEAM MICROWAVE SYSTEMS FOR THE SOLAR POWER SATELLITE E. M. KERWIN, D. J. JEZEWSKI, and G. D. ARNDT NASA Johnson Space Center Houston, Texas 77058, USA Abstract — A generalized antenna design technique is applied to the unique environmental requirements pertaining to solar power satellite (SPS) systems. Optimal illumination tapers and antenna/rectenna sizings are generated which allow increased transmit powers and lower electricity costs while minimizing sidelobe levels to meet a 0.01 mWTcm2 environmental standard. These optimal tapers also provide other advantages over the 10 dB Gaussian reference system. INTRODUCTION The initial design of the solar power satellite (SPS) microwave power transmission system had a 1-km diameter phased array antenna radiating 6.5 GW (gigawatts) of RF energy to a ground receiving/rectifying system (rectenna). A 10 dB Gaussian illumination taper was chosen for the reference system configuration in order to maximize the rectenna collection efficiency and to minimize sidelobe levels (1). The overall system performance included 5 GW of power delivered to a 10 km diameter rectenna at an electricity cost of 46.8 mills per kWh (1 mill = 0.001 dollar). The first sidelobe peak had a maximum power density of 0.08 mW/cm2. A detailed SPS cost model with seven major categories and 34 subcategories was subsequently developed and provides insight into the relative cost factors (2). Based upon this cost model and an antenna optimization procedure to be described, it is now possible to greatly improve the end-to-end microwave system performance. The purpose of this paper is to describe a general ank..na design optimization method which, when applied to the environmental constraints imposed by the SPS system, generates optimal antenna illumination tapers. The developed tapers allow more power to be transmitted and received at a reduced cost while minimizing the sidelobe levels to meet a 0.01 mW/cmz environmental standard. Other benefits include smaller rectenna sizes and fewer geosynchronous satellites. The paper is structured to present the rationale for the reference Gaussian taper, the cost model used for optimization, microwave theory and equations, optimization procedure, and then the results and system configurations. INITIAL TAPER AND SIZING ANALYSIS The initial SPS sizing with a 1-km transmitting antenna and 5 GW of d.c. output power from the rectenna was based upon Ref. 1
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