TABLE 3 SUMMARY OF ANTENNA GAIN CALIBRATION METHODS on units currently available. It has been determined that the positioner must be able to resolve a sample within 0.0016 degrees (corresponding to a 19 bit encoder) to resolve the beam power within a ±0.04 dB accuracy. The positional accuracy of off-the-shelf positioners is on the order of 0.005 degrees. The fractional power in the beam based on a uniformly illuminated 10 m2 aperture is plotted in Fig. 2. Here, it is seen that the main beam (±0.312 degrees) encompasses approximately 79% of the transmitted energy. Approximately 89% of the total radiated power is accounted for within a ±1.5 degree scan, and over 99% of the power is radiated in the ±20 degree sector. Based on these results, the concept illustrated in Fig. 3 was devised. Here, a small angle positioner (SMAP) provides very accurate scan capability over a ±1.5 degree sector for the purpose of beam integration. The larger gimbal arrangement provides coarse positioning over the complete ±20 degree sector. Positioner hardware providing greater angular scan does not currently exist. Measurement Electronics An error sub-budget for receiver electronics is shown in Table 4. The errors allocated to transmitter/receiver sources require advances in state-of-the-art of associated microwave electronics. However, even with currently available equipment, because of single frequency operation and the fact that receiver and transmitter are phase-locked and thermally stabilized, errors can be accurately controlled.
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