基于P波段新型三周期慢波结构同轴相对论返波振荡器设计思想，设计了一个L波段同轴相对论返波振荡器。粒子模拟表明，在二极管电压591 kV、电流8.2 kA、导引磁场0.8 T时，获得了1.50 GW的微波输出，频率为1.64 GHz，效率达31%，器件慢波结构尺寸仅为96 mm×207 mm。分析了该器件实际高频结构的电动力学特性，重点研究了纵向谐振模式、品质因数等特点，并结合P波段的研究结果，得到了该类器件的相关设计指标：慢波结构长度约为一个波长，波纹周期约5/13波长，外波纹深度约1/10波长，内波纹深度约1/30波长，电子束半径约0.7倍外波纹平均半径，器件的纵向工作模式为0.8π模，对应的Q值约16。

Based on a novel compact P-band coaxial relativistic backward wave oscillator(RBWO) with only three periods slow wave structure (SWS), an L-band coaxial RBWO is proposed and investigated. Particle simulation results show that, with the 591 kV, 8.2 kA electron beam guided by the 0.8 T solenoidal field, the microwave is generated with the power of 1.50 GW operating at about 1.64 GHz. The interaction efficiency is about 31% and the optimized size of SWS is only 96 mm×207 mm. Furthermore, the electrodynamics characteristics of the proposed device, expressly the longitudinal resonant modes and quality factors, are analyzed. Finally, a principle of design for low-band coaxial RBWO is presented with the results of P-band coaxial RBWO and L-band coaxial RBWO, i.e., the length of SWS is about equal to the wavelength, the period length of SWS, and the depths of outer and inner conductor ripples are respectively about 5/13, 1/10, and 1/30 times the wavelength, the radius of electron beam is about 0.7 times the average radius of outer conductor ripple, the longitudinal resonant mode is 0.8π mode and the Q-factor is about 16.