Antenna gain measurements using improved radio star flux density expressions

Radio stars have been used to measure the gain of large antennas for many years. The straightforward expressions required, and the simple, direct measurements involved have made this method the most accurate available for this class of antennas. Radio astronomers provided the bases for the technique by measuring the flux density of various celestial sources having strong radio emission at frequencies from 100 MHz to 100 GHz. Many papers have documented measurements which have lead to refinements and improvements in the flux density expressions, as well as other contributing factors such as angular extent corrections and polarization effects. The existing equations extracted from current literature are presented, along with data to support new and improved flux density expressions that provide more accurate results. A solution is presented to discrepancies found when radio sources are used to measure antenna gain. Flux density expressions for radio sources Cassiopeia A (Cas A), Taurus A (Tau A), and Cygnus A (Cyg A) were examined in published data. Using Cas A as a reference, the flux expressions for Tau A and Cyg A were adjusted to eliminate the characteristically lower-than-expected results obtained when these two radio sources are used to measure antenna gain. With these new, improved expressions, Cas A, Tau A, and Cyg A give similar gain results, to within an observable average of /spl plusmn/0.04 dB, for both C-band and Ku-band antennas.