Investigation Of The Technologies For High Power Microwave Mode Conversion And Power Combination

The traditional high-power microwave sources?such as relativistic backward wave tube,virtual cathode oscillator,and magnetic insulated transmission line oscillator?output rotational axis symmetrical mode,such as circular waveguide TM₀₁ and coaxial TEM mode.These modes directly act on the conventional antenna and generate an angular far-field radiation pattern whose axial radiation is zero.The property of low gain and energy dispersion are not suitable for the directional transmission and transmission of high power microwaves.As one of the key component,the mode converter plays an important role in high-power microwave?HPM?system.They mainly rely on adjusting the transmission structure to meet matching requirements.At the same time,since the output power of a single high-power microwave source is limited,multiple microwave sources need to combine the output powers so as to achieve higher power output.In this paper,a new type of coaxial waveguide TEM mode to rectangular waveguide TE₁₀ mode converter is studied.It can achieve high efficiency conversion from high power microwave coaxial TEM mode to rectangular waveguide TE₁₀ mode.The simulation results reveal that,the return loss is lower than-60 d B,and the conversion efficiency is as high as 99.9%,which indicates the mode converter is suitable for the applications.In the rectangular waveguide cavity of this mode converter,the microwave mode is gradually converted from the coaxial waveguide TEM mode to the rectangular waveguide TE₁₀ mode due to the impedance transformation of the tapered pyramid.In order to counteract the reflection at the rear load end of the rectangular waveguide,the shorted end slider is adjusted up and down so that the reflected wave is cancelled in the VSWR cavity to achieve high-efficiency microwave transmission.In order to have a higher power output at the output port,the microwave power splitters/synthesizers based on a rectangular waveguide 4-port microwave power divider/combiner and a 16-port radial line waveguide were studied in this paper.The rectangular waveguide power divider/combiner adjusts the matching and reflection of the common output port through the insert structure in the T-junction waveguide,so that the microwave power is distributed to multiple outputs according to a given ratio.In this paper,by optimizing the design,the four-way equal distribution of the signal power in the rectangular waveguide is achieved,and the phase relationship of each channel is relatively stable.The simulation results show that the return loss of this splitter is less than-30dB,and the transmission efficiency is more than 99%in the synthesizer application.The phase difference of each port in the design frequency band is not more than 1°.The microwave power in the radial line waveguide power divider/combiner is input into the radial waveguide through the coaxial inner conductor extending into the radial waveguide,and then distributed to the multiple output ports according to the equally divided power ratio.This paper optimizes of the design,achieveing 16-way equal distribution of signal power in the radial waveguide with stable relative phases difference of various ports.The simulation results show that the return loss of this splitter is less than-30 d B,and the transmission efficiency is more than 99%in the synthesizer application.The phase difference of each signal in the design frequency band is no more than 1°.The two microwave power dividers/combiners are simple and easy to manufacture and connect to the aforementioned mode converters to form a power synthesis network:coaxial TEM mode output-coaxial-rectangular waveguide mode converter-rectangular waveguide power combiner-common power output,which satisfies the need for microwave power distribution/synthesis in practical engineering.