SOLID-STATE CONFIGURATIONS K. G. Schroeder Rockwell International - Anaheim, California -INTRODUCTION This paper describes two prototype solid-state phased array systems concepts developed by Rockwell for the Solar Power Satellite (SPS). In both concepts, the beam is centered on the rectenna by means of phase conjugation of a pilot signal emanating from the ground. Also discussed are solid-state studies performed at Boeing and Raytheon. The basic Rockwell concepts are now described in more detail. OVERVIEW OF SOLID-STATE ARRAY CONCEPTS Two different solid-state arrays are being developed at this time: The End- Mounted Space System (Figure 1) and the Sandwich (Figure 2). Both concepts use the same element (a dipole) and spacing, but in the end-mounted system 36-watt amplifiers are mounted on the ground-plane, whereas in the sandwich the amplifiers are elevated to the dipoles, and their waste heat is dissipated by beryllium oxide discs. The feed lines are underneath the ground-plane, and a coaxial transmission line is carried all the way to the amplifier input. (See section on RF Signal Distribution). REFERENCE PHASE DISTRIBUTION Phase conjugation at the 5 meter by 5 meter subarray is used to steer the beam. The reference phase signal is distributed over the spacetenna aperture via a radio link. Figure 3 illustrates this method giving a perspective view of the top of the aperture. Two important features are: (a) the phase reference signal originates from a single transmit location at the rear of the aperture; and (b) phase reference and pilot antennas are orthogonally polarized with respect to the power dipoles to avoid feedback loops. Instead of an endfire (e.g., "Cigar") array, broadside arrays can be used for reference and pilot pick-up. Both configurations shall be considered in more detail in future studies. The phase reference signal is distributed as follows: From the shaped-beam illuminator antenna an RF signal is distributed over a cone with maximally 90 degrees beamwidth. All reference pick-up antennas see approximately the same signal strength. The local oscillator and driver amplifer is redundant. Large variations in aperture flatness can be compensated modulo 2 it since bandwidth is of no concern for the reference phase signal. The phase at each subarray pick-up point is normalized with respect to a perfectly flat uniform aperture by means of a servo loop shown in Figure 4. For each subarray center location, a phase delay differential ("reference standard") is computed which occurs for the two generating frequencies f and f 9 if the receiving antenna is located on a perfect plane. These delays canoe calculated, and tuned in the lab to fractions of a degree. The output of the phase bridge then drives a phase shifter until the path delay differential equals that of the reference standard.
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