A precise measurement of the gain of a large horn-reflector antenna

The gain of a horn-reflector antenna with an aperture area of about 400 square feet has been measured with a probable error of 2 per cent at a frequency of 4080 mc. Errors and fluctuations normally introduced into gain measurements by terrain and other environment were obviated by mounting the source on a helicopter which maintained a position about 2500 ft. above ground at a distance of one mile from the antenna under test. It is concluded that high precision can be obtained in measurement of gain of large antennas using such methods.