The extrapolation range measurement technique for determining the power gain and polarization of antennas at reduced range distances is described. It is based on a generalized three-antenna approach and does not require quantitative a priori knowledge of the antennas. During the past decade, it has been extensively used by the National Bureau of Standards, Boulder, Colorado, to calibrate antenna gain standards for industry and other agencies within + or - 0.1 dB. To help one understand how calibrations of the accuracy are achieved, the extrapolation range description includes discussions on the required theory, the measurement procedures, the range configuration and instrumentation, the errors, and some measurement examples. Recent extensions of the extrapolation method required for swept/stepped frequency gain calibrations and for corrections to reduce ground reflection effects, are also presented.
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