对速调型相对论返波管慢波结构色散特性及束波相互作用进行了理论研究。色散特性研究表明：器件工作模式为TM01模，近π点，耦合阻抗较高。色散特性预测的工作频率与粒子模拟结果非常接近。慢波结构峰值增长率相对较小，这与电子束与慢波结构相距较大有关，因而器件从起振到饱和的时间较长。在束波相互作用理论中，全面考虑了电子束与慢波结构前向波基波、反向波－1次空间谐波及空间电荷场相互作用、谐振反射器对电子束进行的束流调制和能量调制作用，以及调制腔和提取腔处引入的耦合阻抗及轴向波数突变。稳态和非稳态计算结果均获得了超过40%的束波转换效率。

The dispersion characteristics of slow wave structure(SWS) and the beam-wave interaction theory are developed for klystron-like relativistic backward wave oscillator. The dispersion characteristics show that the operation mode of the device is TM01 mode, near π point, and the maximum growth rate is relatively small, which is partly due to the larger span between the electron beam and SWS and will result in a larger saturation time. The frequency predicated by the dispersion characteristics is very close to that obtained in previous particle-in-cell simulation. In the beam-wave interaction theory, the 0th space harmonic of forward wave, the -1st space harmonic of backward wave, and the 1st-order beam space-charge wave are taken into account. The resonant reflector provides pre-modulation for beam current and electron energy, and the modulation cavity and extraction cavity introduce larger changes in coupling impedance and phase velocity. Both steady state and unsteady state calculations show that beam-wave conversion efficiency of above 40% can be obtained.