利用速调管放大器中间腔可以提高器件放大增益，并达到降低微波注入功率的要求，同时针对高功率微波相对论速调管放大器的特点，建立了一个带有两个中间腔的S波段相对论速调管放大器，采用特殊结构克服了多个中间腔引入的高次模影响，模拟上实现了在kW量级微波注入条件下，基波电流调制深度达到80%，输出微波3.3 GW。

The introduction of bunching cavities can significantly increase the gain of relativistic klystron amplifier, and correspondingly the power of the seeding microwave can be reduced to a very low level. Though higher gain can be obtained with more bunching cavities, the self-exciting problem will seriously disturb the working mode in the device. A special structure is introduced to deal with such problem. Based on the engineering requirement, a S-band of 3 GW relativistic klystron amplifier is designed with the seeding power 20 kW. In the simulation, the fundamental current modulation depth is 80% and the output microwave power reaches 3.3 GW with the seeding power of kilowatts.