Abstract: The optimization method of horns that combine axial and radial slots was studied. Body of revolution finite difference time domain algorithm was applied in analyzing horns. A corrugated horn working in the Ku band was designed and optimized using covariance matrix adaptation-evolution strategy for better aperture efficiency. The optimized horn was fabricated and tested. Simulated and measured results show a good agreement in both impedance matching and radiation patterns in 10.7-12.75 GHz. The aperture efficiency is better than 78% with the feed illuminating a classical Cassegrain antenna, which proves the effectiveness of this optimization method.