Theoretical Research And Simulation Of A 220GHz Extended Interaction Klystron

Terahertz is between infrared waves and millimeter wave. Klystron occupies an important position in the microwave tube, with high gain, high power, high reliability and so on. Klystron extended interaction is one of the best choice in the terahertz band. Traditional klystron with single gap may cause the loss and breakdown when working in high frequency. To solve the problems, multiple interaction gaps in every cavity is applied.In this text, the development and characteristics of the terahertz devices and extended interaction klystron are introduced. The present development situation both home and abroad are summarized and reviewed. The working principle of klystron is introduced and bunching theory and coupling coefficient is derived. The resonator is analyzed from the aspect of the equivalent circuit. The expression of the lumped and characteristic impedance of cavity was deduced, and equivalent parameters of the multiple interaction resonator and the extended interaction resonator are analyzed. Space-charge theory and equivalent circuit theory are considered to derive small signal gain of the multi-cavity klystron. The expression of the small signal gain with a four cavities is deduced.In the design of the extended interaction klystron amplifier, the cavity structure, work mode and period and some of the parameters are analyzed and determined. The rectangular trapezoidal slow wave structure is selected as the cavity structure and 2π mode as the working mode. With the integrated model, the high frequency characteristic of the extended interaction klystron is simulated, amplifier are accomplished. With an electron beam of 16.5 kV and 0.03 A, an average power of 4.5 W with frequency of 214.66 GHz, gain of 23.5 dB, 3dB band-with of 234 MHz, power conversion efficiency of 0.9% is obtained, which matches the small signal calculation program with a maximum gain of 21.45 dB. Under the small signal program, some parameters are changed to get the maximum gain variation curve. According to the variation,another model with big signal is designed. With an electron beam of 18 kV and 0.15 A, an average power of 160 W with frequency of 213.85 GHz, gain of 39.5 dB, 3dB band-with of 310 MHz, power conversion efficiency of 6% is obtained. And a brief analysis of the reasons for the changes of parameters of the result is given.