Theoretical And Experimental Study Of High-Power Microwave Waveguide Filter

Limited by physics and technologies,the output capacity of a single high-power microwave?HPM?source can hardly be further improved.To overcome the difficulty,it is an effective approach to obtain higher output levels by utilizing waveguide-based power combining technologies,which is to combine several HPM sources to enhance the output capacity.As the key part of the technologies,it is of great importance to study HPM filters with high power capacity and transmission efficiency.Therefore,in this dissertation,based on the detailed mode matching analysis of discontinuities in conventional waveguides,several HPM filters are designed through Genetic Algorithm?GA?.The corresponding simulations and experiments are also carried to further testify the properties of the filters.The detailed contend of the dissertation includes the following parts:1.Based on the mode matching coefficients of circular waveguide discontinuities,several circular waveguide filters with high transmission efficiency and power handling capacity are proposed and tested.Through mode matching theory,the mode matching coefficients caused by circular waveguide discontinuities are strictly derived.At the same time,a new genetic algorithm program is written by the author to improve the accuracy and efficiency of the traditional filter design procedure.On the basis of program and mode matching coefficients,two TM₀₁ mode circular waveguide filter are designed to substitute for the filters designed before.Simulation results show that the central frequencies of two filters are 9.3GHz and9.7GHz separately,and the transmission efficiency at central frequency exceeds 99%.The bandwidth of both filters is 300MHz and the power capacity exceeds GW level.In order to further improve the power capacity,a TE₀₁ mode circular waveguide filter with central frequency of 9.3GHz and 400MHz bandwidth is designed and fabricated.The cold test results of the filter indicates that transmission efficiency within the passband is over99%which agrees with the simulation results.2.Several coaxial waveguide filters are proposed and tested on the basis of the derived mode matching coefficients to improve power handling capacity.By using mode matching theory,the discontinuities in coaxial waveguide are analyzed.Two bandpass filters based on coaxial waveguide are designed by means the written GA program.Simulation results demonstrate that transmission efficiency of both filters within 200MHz passband is over 98%and the power handling capacity exceeds10GW.Coaxial waveguide filter working at 9.3GHz is fabricated and tested.No breakdown and pulse shortening phenomenon is caused in the HPM experiment,which proves the power handling capacity of the filter.3.Several radial waveguide filters are designed after the derivation of the mode matching coefficients.To meet requirements of application,a radial waveguide filter which can separate transmission mode is innovatively put forward.Based on the analysis of the radial waveguide discontinuities,the mode matching coefficients are strictly derived.As no electric field enhancement will be caused when transmitting TE₀₁ mode,three single-mode radial waveguide filter is designed through equivalent-circuit model.Simulation results show that all bandwidths are about 150MHz and the passband transmission efficiency of all filters is over 99.8%.At the same time,an over-mode radial filter with a 500MHz bandwidth is also proposed to improve the narrow bandwidth of single-mode filters.The transmission efficiency within the passband of the over-mode filter is more than 99.8%and the stopband attenuation is lower than-15dB.Besides,a radial waveguide filter which can separate TE₀₁ mode and TEM mode is innovatively put forward.Within the frequency band of 9.2GHz to 9.8GHz,the transmission efficiency of TE₀₁ mode is over 99.5%and TEM mode is totally cut off.