The radiation of a circular cylindrical reflector antenna in the presence of imperfect flat earth is treated in an accurate manner. The boundary value problem is formulated in terms of a full-wave integral equation converted to the dual-series equations and then regularized by using analytical inversion of the static part. The resulting Fredholm second-kind matrix equation is solved numerically with guaranteed accuracy. The feed directivity is included in the analysis by using the complex source-point method. Various antenna features, which include the overall directivity, efficiency, gain, and radiated and absorbed power fractions have been calculated and compared with the free-space antenna characteristics. They show some phenomena not predicted by approximate techniques.