Abstract: In the field of high-power microwave radiation, mode converter and horn antenna are commonly used technologies to achieve rotational axisymmetric mode-directed radiation, but the separate design of mode converter and horn antenna often results in a large axial and aperture size of the antenna. To meet the demand for miniaturization of antennas in actual application scenarios, a stepped double semicircular waveguides radiation antenna with mode control and radiation integration is proposed. The antenna is fed with a circular waveguide TM₀₁ mode and divided into two 180° phase difference semicircular waveguides by a plate. Then, two asymmetric stepped semicircular waveguide radiation elements are connected to achieve microwave radiation. The power divider uses a gradually tapered circular waveguide for matching, and a large inner conductor is used to improve power capacity. The dual semicircular waveguide radiation elements use the mode matching method combined with the Particle Swarm Optimization algorithm for phase adjustment and mode control. By integrating mode control and radiation in a multi-region design, a more uniform co-phase electric field distribution is achieved at the radiation aperture, achieving directed radiation, thereby shortening the antenna length and reducing the aperture size. An antenna model with a center frequency of 2.85 GHz is optimized, with dimensions of 1.18λ×1.18λ×2.42λ. Simulation results show that the return loss of the antenna is greater than 15 dB in the 2.75−2.96 GHz band, the realized gain is greater than 15.5 dBi in the 2.71−3 GHz band, the realized gain at the center frequency is 16.14 dBi and the vacuum power capacity is 906 MW. Compared with the traditional mode converter and horn antenna technology route, the proposed antenna has the characteristics of high power capacity and miniaturization.