Study On Cold Circuits Of Confocal Gyro-TWT In Submillimeter Wave Band

Since the 21st century,with the rapid development of radar,precision guidance,electronic countermeasure,high-speed communication and microwave biology,the development of high-power millimeter wave devices have attracted more and more attention^[1-2].Gyrotron traveling wave tube is a kind of electric vacuum device based on the mechanism of electron cyclotron maser.It has the advantages of wide bandwidth,high gain,high efficiency and high power.It is limited by size shrinking with the increase of frequency,resulting in lower power capacity,and severe electron interception problem.Choosing higher-order mode as the working mode can effectively increase the interaction size,but it will bring mode competition problems to gyrotron devices.In addition,the smooth circuit in gyro-TWT is easy to induce parasitic oscillations of different modes,resulting in low output power or even instability^[3-4].Fortunately,Massachusetts Institute of Technology(MIT)proposed two novel mode-selection circuits including the confocal waveguide and photonic band gap waveguide.It weakens the mode competition and improves the stability in higher-order mode operation.After years of research,the output performance of confocal waveguide gyro-TWT is far from realizing its advantages of high gain and high power.However,in order to provide a vacuum environment,the ideal open boundary of confocal circuits cannot be realized in practical applications.Therefore,it is of great significance to study the dispersion and loss characteristics of the confocal waveguide with different boundary conditions for practical application.The main research work of this thesis is as follows:(1)Simulation study on the cold cavity of W-band confocal circuits with different boundary conditions is carried out by using three-dimensional electromagnetic simulation software,and the dispersion relation and diffractive loss characteristics are studied.It is found that the lossy dielectric ring circuit can improve the stability,it can effectively absorb the diffraction wave as the radius and thickness of the dielectric ring are greater than a certain value,and it has wide adjustment range and does not need high-precision processing technology.(2)Simulation study on the cold cavity of G-band confocal circuits with different boundary conditions is carried out by using three-dimensional electromagnetic simulation software,and the dispersion relation and diffractive loss characteristics are studied.A confocal circuit loaded with wedge-shaped conductor is proposed.It is capable of guiding the outward radiation wave,so that the dielectric material can well absorb the diffraction wave,which greatly improves the stability of the tube.It is found that an inclination angle of 30°-55°of the wedge works well at G-band.