Ύϊΐ€ mcNtn has been successfully used as a calibrated source of RF emissions in determining the gain-to-noise-temj^rature ratios (G/T^s) of medium size €-band antennas. This method to determining G/T has recently been applied to K^-band antennas as well, and the results have agreed well with independent measurements of gain and temperature. However, because of the fact that the moon's angular diameter may extend beyond the main lobe of lobe antenna, a gain correction factor has to be applied. This factor requires accurate knowledge of the gain pattern for its determination, but once such knowledge has been obtained by pattern measurement, the G/T can be calculated with reasonable accuracy.