对Ka波段TM02模式低磁场相对论返波管的结构特点、工作原理进行了介绍，详细分析了该器件以TM02模工作的模式选择机制。通过粒子模拟，该器件在1 T引导磁场下获得了功率为493 MW、频率29.3 GHz的微波输出，工作模式及频率与理论设计相一致。随后，基于模拟中的结构参数开展了初步的实验研究，当二极管电压为580 kV、电流为3.56 kA、引导磁场1 T时，获得了功率286 MW、频率29.3 GHz、脉宽约10 ns的微波输出。实验获得的微波频率与数值模拟一致，但是微波功率与数值模拟结果有明显差异，并且微波脉冲后沿有明显的缩短，分析认为在低磁场下后端谐振腔链受到电子轰击是导致该问题的主要原因。

The structure and working principle of a Ka-band RBWO operating at TM02 mode with low guiding magnetic field was introduced, and mechanism of the TM02 mode selection was analyzed. The PIC (particle-in-cell) simulation shows the output power and frequency of the RBWO were 493 MW and 29.3 GHz respectively with guiding magnetic field of 1 T. The operating mode and frequency were corresponding to the theoretic design. The experiment study was done based on the parameters in simulation. A 29.3 GHz millimeter wave with an output power of 286 MW and pulse width of 10 ns was obtained at guiding magnetic field, diode voltage and current of 1 T, 580 kV and 3.56 kA respectively. The frequency of microwave in experiment was in accordance with that in simulation. However, the output power in experiment was much lower, and the pulse width was shortened at post end evidently, which was considered as a result of electrons bombarding at the post cascaded resonators.