Abstract
In this paper we present improved formulations for the extended source size correction factors that are widely utilized in circular aperture reflector antenna gain measurements. Extended radio sources having an angular size that is comparable or larger than the FWHP antenna beamwidth are often used to determine the directivity of the antenna aperture. The resulting directivity measurements must be corrected to account for the convolution of the extended source angular size with the antenna's far field pattern beamwidth. Two kinds of extended radio sources, having either uniform or Gaussian brightness distributions over the source disk, as well as three kinds of the antenna aperture distributions: "Polynomialon-Pedestal", Gaussian, and Taylor have been considered. The existing approximate formulae for the extended source size correction factor are examined and compared to the improved formulations.