Fig. 11. Near-field measurement facility concept. CONCLUSIONS Because of the large electrical size of the SPS subarray panels and the requirement for high accuracy measurements, specialized measurement facilities are required. Measurement error sources have been identified for both conventional far-field and near-field techniques. Although the adopted error budget requires advances in state-of-the-art of microwave instrumentation, the requirements appear feasible based on extrapolation from today’s technology. Key development items identified include an adequate reference antenna gain standard, a stable precision amplitude (oscillator) standard, and a computer compensated and calibrated phase locked microwave receiver. The possibility of utilizing near-field measurement techniques were studied. With adequate probe calibration and precision mechanical scanning, full 30 by 30 m mechanical module antenna measurements may be performed. The performance and relative cost considerations between planar near-field and conventional far-field methods indicated the overall costs to be roughly the same. Acknowledgements — The following individuals are recognized for their valuable contributions: Dr. E. B. Joy and C. E. Ryan of Georgia Tech in the area of near field measurement techniques; J. L. Detwiler and S. P. Davis of Scientific Atlanta in the area of antenna positioners and electronics; P. F. Wacker of NBS, and B. L. Ulich of the University of Arizona for antenna gain calibration techniques; and W. Finnel of NASA MSFC in the area of SPS system philosophy. This work was supported by MSFC Contract NAS8-33605; Contract Technical Monitor was R. A. Inman.
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