为了解决目前3 mm回旋行波管所使用的蓝宝石输出窗因功率容量不足而发生破裂的问题。从抗热震性和功率容量两个方面出发，对常用的几种窗片材料进行了对比。在国内首次以微波等离子体化学气相沉积金刚石为窗片材料，利用数值计算及ANSYS软件仿真设计了用于3 mm回旋行波管的低反射，低吸收，宽带宽，高功率容量的输出窗。结果表明，所设计的输出窗适用于TE01模式输出，其S11参数小于-20 dB的带宽为6 GHz。同时，该输出窗具有良好的抗热震性，在自然对流散热条件下具有61 kW的功率容量。

The sapphire window for 3 mm gyro-traveling wave tube(TWT) can not meet the design requirement of power capacity. To solve the problem, comparisons of several materials in power capacity and thermal shock resistance are carried out. A microwave plasma chemical vapor deposition(MPCVD) diamond window of low reflectivity and absorption for 3 mm high power gyro-TWT is designed by using numerical calculation and simulation. The results indicate that the designed MPCVD diamond window is appropriate for outputting TE01 mode, the bandwidth in which S11 is less than -20 dB is about 6 GHz. In addition, the thermal shock resistance of the window is good and the power capacity is about 61 kW in the condition of natural convection heat dissipation.