在速调管放大器中，中间谐振腔一方面可以提高器件的放大增益，另一方面也容易产生杂频振荡，影响器件正常工作。针对这种杂频振荡的影响，在三腔相对论速调管的基础上发展了四腔相对论速调管。采用PIC粒子模拟软件从整管上对四腔强流相对论速调管放大器的冷腔结构、束波互作用、微波提取等方面进行研究。为得到输出功率和效率的最优值，结构上采用低互作用输入腔，设计了阶梯状结构漂移管，通过对输出腔作用间歇进行优化处理抑制电子回流。模拟结果表明整管微波模拟输出功率达了3.7 GW，效率22%，增益56 dB，1 dB带宽74 MHz，并实现了对杂频振荡的抑制。

In a relativistic klystron amplifier (RKA), the idle cavity can increase the gain of the device, but the oscillation of nonworking modes will occur in the same time, and therefore the performance of RKA will be significantly decreased. We developed a four-cavity relativistic klystron on the basis of three-cavity relativistic klystron to study the mechanism of nonworking modes’ oscillation. A PIC particle simulation software was used to study the cold cavity structure, beam-microwave interaction and microwave extraction of output cavity. An input cavity with low interaction impedance and a ladder structured drift were adopted in the structure to avoid nonworking modes’ oscillation. By optimizing the output cavity gap, the returning electrons had been significantly reduced, and thus the oscillation of nonworking modes was not excited. Finally, the output microwave with a power of 3.7 GW, a gain of 56 dB, an efficiency of 22% and 1 dB bandwidth of 74 MHz were achieved in simulation with the discussed structure.