Exact gain measurement of large aperture antennas using celestial radio sources

The correction factors for angular extension of celestial radio sources, Cassiopeia A (Cas A), Taurus A (Tau A), and Cygnus A (Cyg A) were calculated based on the detailed contour maps of brightness temperature. Examinations of the flux densities of those radio sources were made using the published data. The gain of antennas of several sizes measured by using the three radio sources was determined by applying the newly obtained parameters. It was found that the gain of large aperture antennas at 4- and 6-GHz bands could be determined to the accuracy of better than
\pm0.45 dB (3\sigma)
by use of the three radio sources.