Investigation On V-band Coaxial Cerenkov High Power Microwave Oscillator

Promoted by the application requirements of directional energy,electronic counter-measure,material processing and radar,the development of high power microwave gen-erators towards V-band millimeter wave is an important trend.Among all kinds of high-power microwave sources,coaxial Cerenkov oscillator is expected to become the main technical scheme for the millimeter wave high-power microwave sources due to its high power and high efficiency.Under such background,a coaxial overmoded high-power mi-crowave oscillator based on Cerenkov mechanism is proposed,focusing on the feasibility of coaxial slow wave devices applying in the V-band.The key problems such as mode control and electron beam transmission are systematically studied and verified by exper-iments.The research results provide the possibility for the application of coaxial slow wave devices in V-band.The research contents include the following aspects:1、The high frequency characteristics of symmetric and asymmetric modes in coaxial devices are systematically studied.Based on the guided wave theory and plasma theory,the dispersion relationship and growth rate of symmetric and asymmetric modes in coax-ial slow wave structures,as well as the reflection and resonance characteristics of coaxial discontinuous structures are numerically calculated,which improves the computational efficiency of large overmoded coaxial de vices.The field distribution,power capacity,quality factor,coupling impedance and growth rate are comprehensively analyzed,which provides the theoretical support and improves the design efficiency.Compared with pre-vious researches,the problems of low power capacity,narrow electron beam channel and difficult mode control are solved th eoretically.The theoretical framework of large over-moded coaxial Cerenkov oscillator is improved.2、The preferential excitation mechanism of asymmetric modes in coaxial slow wave structures is studied in detail,and a new method to suppress asymmetric modes is pro-posed.The quasi-TE_v1mode has higher quality factor,lower starting current and higher growth rate than the quasi-TEM mode,so it is easier to be excited.To solve this prob-lem,two new and efficient asymmetric modes suppression methods,hybrid mode cou-pling method and reflection adjustment method,are proposed.Applying those methods in millimeter wave band can not only effectively suppress the asymmetric modes,but also effectively expand the electron beam channel and solve the problem of electron beam transmission in high frequency band.3、The universal design method of V-band coaxial Cerenkov oscillator are analyzed theoretically,and the complete design process including coaxial slow wave structures,re-flection cavity and mode purifier are given.Based on this process,a new structure of over-moded coaxial Cerenkov oscillator operating in V-band is proposed.The device adopts the improved segmented slow wave structures,which has the advantages of high power efficiency,stable operation state and wide electron beam channel.Three dimensional simulation results show that the high power microwave with frequency 62.6 GHz,power335 MW and efficiency 32%can be obtained under electron beam voltage 355 kV and current 3 kA.4、The V-band coaxial Cerenkov generator is experimentally studied.The experi-mental results show that when the diode voltage is 350 kV and the guiding magnetic field is 2.0 T,the output microwave with power 239 MW,frequency 63.2 GHz and pulse width18 ns can be measured.The device is compact and the operation state is stable.The oper-ation mechanism is consistent with the simulation design.The measured power and pulse width are the highest levels publicly reported in recent years.