Research On The Gain Equalizer And The Mode-Discrimination Filter For Gyrotron Travelling Wave Tubes

The gyro-traveling wave tube has the potential to be applied in the high-resolution imaging radar,high-data-rate long-distance communication system and other fields with its characteristics of high power,wide frequency band and high gain.In practical applications,it is combined with a solid-state power amplifier to form a high-power millimeter-wave power amplifier system,which greatly improves the power performance.However,the output power of the solid-state power amplifier does not match the input power of the gyro-traveling wave tube,which will cause a large fluctuation in the outpt gain.Between the solid-state power amplifier and the gyro-traveling wave tube,a microwave gain equalizer is required to achieve a flat output gain.For the output end of the high-frequency system(above the W-band),the electromagnetic wave has self-excited oscillation in working mode and backward-wave oscillation in non-working mode.When an oscilloscope displays these signals,there is interference from the spread spectrum of the local oscillator frequency and the image frequency,resulting in a relatively cluttered spectrum.In order to eliminate the interference,it is necessary to design bandpass filters with different passbands to separate the modes.The specific research contents and results of microwave gain equalizer and waveguide filter in this thesis are as follows:In terms of microwave equalizers,it is a pioneering work in the application field of the gyro-traveling wave tubes.Taking the design of Ka-band as an example,two types equalizers of reflection type and transmission type are proposed in this thesis.Compared with traditional equalizers,these types of equalizers completely adopt metal waveguide structure,which greatly improves the power capacity.The reflection-type equalizer has a simple structure and is easy to adjust.The error between the equalization effect and the target is small.However,the port reflection is very large.And if it is used directly,the pre-stage solid-state power amplifier will be damaged.The designed transmission-type microwave gain equalizer is divided into two types:3-port type and 4-port type.The 3-port transmission-type equalizer solves the problem of large port reflection in the reflection-type equalizer,and the different improved structures make the equalization effect match the target better.The 4-port transmission-type equalizer reduces the port reflection to a lower level while maintaining a good aggrement between the equalization and the target.The reflection-type equalizers and some 3-port transmission-type equalizers have been fabricated and measured,and the measurement and simulation results are in a good agreement.The 4-port transmission-type equalizer has only been simulated and not measured.In terms of mode-discrimination filters,some waveguide band-pass filters that work in the W-band and around 220 GHz are designed in this thesis.The W-band filter is based on the General Chebyshev filter principle.The cross-coupling structure is adopted here.A transmission zero is generated at each end of the passband,and the position of the transmission zero can be adjusted.The mode-discrimination filters are designed respectively in TE₀₁ working mode(92 GHz?100 GHz),TE₀₁ cut-off oscillation mode(86 GHz?92 GHz),TE₂₁ oscillation mode(passband 72 GHz?78 GHz)and TE₁₁oscillation mode(62 GHz?69 GHz).Insertion loss is lower than 0.1 d B.The return loss is higher than 20 d B,and out-of-band rejection at 1 GHz at the low end of the passband is higher than 20 d B.In the 220 GHz frequency band,a multi-mode cavity bypass coupling structure is adopted,which reduces the size sensitivity.A transmission zero is generated at each end of the passband,and the position of the transmission zero can also be adjusted.The passband of the designed filter is 205.7 GHz-224 GHz.The insertion loss is lower than 0.1 d B.The return loss is higher than 18 d B,and the out-of-band rejection at the low end of the passband at 1.37 GHz is higher than 20 d B.The filter of W-band is fabricated and measured,and the error between the measurement and the simulation is analyzed in detail.The 220 GHz mode-discrimination filter has only been simulated and optimized,and has not been measured.