TABLE 1 MEASUREMENTS ERROR BUDGET FAR-FIELD MEASUREMENT CONCEPTS Measurement Accuracy Considerations The predominant error contributors for far-field measurements are |1] field nonuniformity due to ground reflection, |2] gain loss due to quadratic phase error (near-field effects), and extraneous reflections. The National Bureau of Standards has investigated error budgets associated with far-field measurements (3). The large size of an SPS subarray dictates a far-field criteria of greater than 6 D2/X to maintain quadratic phase error loss below 0.01 dB. Field nonuniformity can be controlled via an elevated range concept where the receive antenna null is placed at the midpoint reflection point as depicted in Fig. 1. Trade-off calculations indicate the required tower heights for elevated range dis-
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