Abstract: This paper addresses the numerical analysis method for a circular waveguide bevel cut radiator (Vlasov-Nakajima radiator) which is used as the first step in the design of a high power microwave Vlasov-type mode converter. The radiation field launched from the radiator can be considered as the sum of the field radiated by the circular aperture and the field scattered by the bevel cut. The former is predicated by Kirchhoff-Kottler integration. The latter is calculated by physical-optics approach. Numerical far-field radiation patterns are compared to measured results. The theoretical analysis of the frequency characteristic of the radiator shows that it has luminary electrical scan ability.