A novel coaxial relativistic Cerenkov generator (CRCG) operating in quasi-transverse electromagnetic mode is proposed for generating Ku-band high-power microwave radiation. It is found that using a cathode with a shielding electrode can decrease the diffusing electric field in the diode, thereby allowing a CRCG with the proposed diode structure to operate in a low guiding magnetic field. Taking advantage of the two-sectional slow wave structure, the output power and conversion efficiency are improved. Furthermore, a simple optimization rule is proposed for the length of the drift cavity and is verified by numerical simulation. In a particle-in-cell simulation, when the diode voltage and beam current are 550 kV and 4.2 kA, respectively, the microwave with an output power of 1 GW at 15.3 GHz is achieved in a guiding magnetic field of 0.35 T, yielding a conversion efficiency of 43%.
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