An accurate absolute gain calibration of an antenna for radio astronomy

The methods used to determine the absolute gain of an 80-square foot aperture horn-reflector antenna over a frequency range from 2.8 to 14.0 Gc, and in the absence of a high-level test range, are described. A "mirror" range, in which the size of the smooth reflecting surface required was relatively small, was used and the measurements were performed in the Fresnel zone of the antenna with corrections applied for the resulting gain reduction. These and other provisions reduced the probable error in the final values to about one per cent.