Abstract: In this paper, Vlasov antenna is studied systematically by the moment method (MM) and finite difference time domain (FDTD). Based on the simulation results, the process of mode conversion in the waveguide and radiation through the aperture is described in more details by clear physical pictures. The measurement results agree well with the numerical results. Furthermore, a new design of Vlasov-type antenna together with a radome, which will be used in a high power microwave system, is proposed. Compared with the traditional designs, the antenna gain has been increased by 6dB, and the first side lobe level has been decreased by 13dB.