.70 Ghz, Second Harmonic High-frequency Harmonic Gyroklystron System

The frequency-doubling gyroklystron amplifiers not only can produce high pulsepower and high average power in millimeter and sub-millimeter wave bands withmoderate bandwidth, but also because of the harmonic and frequency-doubling property,it needs very low magnetic field, low frequency and power of the input signal. And thismade it become a good candidate sourse of high power THz microwave. So greatmilitary countries pay attention to development of frequency-doubling gyroklystronamplifier's research, and spend a lot to develop them. Its research had become the frontand hotspot in the field of high power microwave and THz sourse.In this paper, the single and multiple abrupt section were studied usingmode-matching technique and scattering matrix formulation. A high frequency circuit ofa four cavities 70-GHz second-harmonic frequency-doubling gyroklystron has beenstudied in this method. The problem of mode conversion of the TE₀₂ mode is studied.A effective method is used to reduce the RF crosstalk of the 70GHz TE₀₁ mode betweencavities for drift section not cut off.The input coupler of gyroklystron is simulated and optimized by HFSS. A method,which combine theory and simulation, is proposed to solve the problem of calculatingthe purity of modes in coupler. The influence of the number and position of slots to thecoupling efficiency and purity of the modes were studied.The ballistic bunching theory was used to calculate and optimize the nonlinearproperty of the output cavity of gyroklystron. The results show that the prebunchingcould improve the interaction efficiency, even on second harmonic, the high efficiencycould achieved also.A 70GHz second-harmonic frequency-doubling gyroklystron with four cavities hasbeen studied. The Q factor and mode conversion of the bunching cavities were studiedin detail with field matching analysis to reduce the RF crosstalk of the 70GHz TE₀₁mode between cavities. And the RF circuit was designed and optimized to enhanceoperating bandwidth and electron efficiency. And then a 70GHz second-harmonic frequency-doubling gyroklystron was designed. 256kW output power, 44dB saturationgain, 28% electron efficiency can be obtained with about 160MHz instantaneousbandwidth were obtain by PIC simulation at 70-kV, 13A electron beam.The two kinds of first harmonic gyroklystron which working in TE₀₁ mode and TE₀₂mode was simulated too. When working in TE₀₁ mode, 406kW output power, 46dBsaturation gain, 48.3% electron efficiency can be obtained by PIC simulation at 70-kV,12A electron beam. While working in TE₀₂ mode, 708kW output power, 47dBsaturation gain, 50.6% electron efficiency can be obtained by PIC simulation at 70-kV,20A electron beam.