Design Of Multi-frequency Relativistic Backward Wave Oscillator With Mode Conversion

Relative backward wave oscillator is often used as multi-frequency and high-power microwave sources due to its high efficiency and high power.The main radiation pattern of the traditional relativistic backward wave oscillator is the TM₀₁ mode,and the radiation pattern of the TM₀₁ mode electromagnetic wave is a hollow cone.If it is radiated directly through the antenna,the radiated microwave energy cannot be effectively utilized.In engineering,in order to improve the transmission efficiency of the device,it usually requires special mode conversion technology to carry out pattern conversion,which often leads to the problems such as the size of the device is too large or the input shaft and the output shaft are not coincident.In this paper,a relativistic backward wave oscillator which can directly radiation multifrequency TE₁₁ mode electromagnetic wave was designed.We relied on the backwave property of the backward wave oscillator,which is that the propagation direction of the wave is opposite to the motion of the electron beam,and the single-fold bidirectional spiral Bragg structure is used to reflect the backward propagating TM₀₁mode electromagnetic wave into the forward wave of TE₁₁ mode.And the single-fold bidirectional spiral Bragg structure,as an oscillator of a stable backward wave oscillator,can not only generate stable high-power microwave oscillator,but also act as a Bragg reflection cavity to convert the electromagnetic wave of TM mode to the electromagnetic wave of TE mode,so as to realize the multi-frequency and high-power output of TE₁₁.The main work of this paper is embodied in the following aspects:1,Three basic equations of relativistic backward wave oscillator ware given,and the dispersion relation and coupling impedance of slow wave structures ware discussed.And the factors affecting the output microwave frequency of relativistic backward wave oscillator ware analyzed in detail,the research status of TM₀₁-TE₁₁ mode converter was summarized,and the Bragg mirror can be used as a mode converter was proposed.2,The coupled wave equation and dispersion equation of the threaded Bragg structure ware given,and a single folding bidirectional spiral Bragg structure was proposed.The TM₀₁-TE₁₁ reflection coefficients of the structure ware numerically calculated and simulated.3,We analyzed and compared several common methods of studying high-power devices,and then designed a dual-frequency relativistic backward wave oscillator with mode conversion using CHIPIC particle simulation software.With 600k V electron beam voltage,8.2k A current and 2.5T axial guided magnetic field,the device could radiate TE₁₁ mode dual-frequency high-power electromagnetic wave,the dual-frequency frequency ware 7.5GHz in C-band and 10.2GHz in X-band,respectively.The peak output power was about 1.15GW,and the average power value was about410MW.4,The dual frequency relativistic backward wave oscillator with mode conversion was further studied,the main factors affecting the performance of the device ware analyzed,and the independence of the two-section slow wave structure was studied.