One of the candidate phasing schemes, retrodirective phase control, is schematically shown in Fig. 6. A pilot beam signal transmitted from the space station is received at each subarray within the satellite microwave antenna. The phase delay of the pilot beam is measured at each subarray and the conjugate phase is provided to the subarray's power tube. Each subarray acts as a unit antenna, with uniform amplitude and phase across its surface. A single coherent beam is formed from the contributions of all the subarrays and is focused at the center of the space station rectenna. The beam is received and converted from RF energy to DC within the receivingrectifying antenna also called the rectenna. The rectenna, as shown in Fig. 7, is composed of half-wave dipoles individually feeding half-wave diodes. The ground plane is a steel, open-mesh reflector with approximately 80% transparency. Orbital drag associated with a rectenna is minimal due to its transparent characteristic. A typical 100 kW beam pattern with power densities of 32 mW/cm2 at the center and 2.4 mW/cm2 at the edge of the rectenna is also shown in Fig. 7. The transfer of larger amounts of power would require larger rectennas in order for the diodes to handles the increased loading.
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