Research On Power Transmission And Divide Technology Of High Power Over-mode Waveguide

In the system of high-power radial line helical array antenna,high-power microwave source and subarrays are connected by waveguide power-divider-network made up of different waveguides.During the process from microwave energy inputting to antenna radiation,these waveguides need to achieve specific microwave transmission,energy distribution,mode conversion,etc.,and their performance is the key to the design of the entire antenna system.However,it is difficult for the existing waveguide structures to meet the requirements of power capacity and turning radius of the antenna system at higher frequency.Therefore,it is of great significance to research on waveguide structures of different levels and corresponding technologies.In this thesis,through physical analysis,theoretical calculation,simulation optimization and experimental verification of these waveguide structures,the features of high efficiency,high power capacity,small bent radius and low losses are achieved.Firstly,in order to connect to the output port of the high-power microwave source and achieve the energy transfer between different planes,the thesis designs a high power over-mode bent waveguides for circular waveguide TM₀₁ mode transmission.The structure uses a high over-mode circular waveguide and an embedded metal conductor to realize bending transmission of high energy electromagnetic wave.By controlling the arrangement of the metal plates,undesirable high-order modes are avoided.And through adjusting the size of the sector waveguide,high efficient energy transmission and small bent radius can be bring about.In addition,this method can be also utilized in bending transmission of coaxial TEM mode or multi-angle circular waveguide TM₀₁ mode.Simulation and experiment show that the reflection of circular waveguide TM₀₁ mode is less than-45dB at the center frequency,the insertion loss is less than 0.2dB,and transmission coefficient is higher than-0.1dB in the frequency range of 8.25-8.55GHz.The power capacity under vacuum is about2.8GW,and its bending radius is very small,only 38mm.Secondly,a waveguide structure of over-mode circular waveguide TM₀₁-four way over-mode rectangular waveguide TE₁₀ mode is presented.At the junction of over-mode circular waveguide and over-mode rectangular waveguide,using embedded metal conductors,the orthogonal bending transmission of four-way sector waveguide TE₁₁ mode is realized.In that way,microwave resonance brought by high-order mode is eliminated and energy efficiency and working bandwidth is improved.The simulated results show that power capacity of the structure is about 2.9 GW under vacuum.At 8.4 GHz,the reflection coefficient of circular waveguide TM₀₁ mode is less than-51dB,and the transmission coefficients of four-way rectangular waveguide TE₁₀ modes are all higher than-6.01dB.Thirdly,in order to cascade multi-stage over-molding rectangular waveguide structure,we present an over-mode rectangular waveguide bent structure and a power divider.With a reasonably-arranged metal plates and wedge,the two can suppress the high-order mode named rectangular waveguide TE₂₀ mode over the entire operating band and eliminate the unbalanced output of microwave energy on both sides of the center frequency after microwave transmission undergoes multiple-level rectangular waveguide power divider.The simulated results give that the reflection and transmission coefficients of rectangular waveguide TE₂₀ mode are less than-40dB in the frequency range of 8-8.8 GHz,and power capacity of the two is in GW level under vacuum.Finally,in order to achieve microwave mode conversion and energy transmission between two different planes,the thesis presents an over-mode circular waveguide TE₁₁-TM₀₁ orthogonal mode converter.In the mode converter,metal plates are utilized to divide over-mode circular waveguide into two way semicircular waveguides at the bend.And mode conversion can be implemented by controlling phase difference of two semicircular waveguide TE₁₁ modes.Circular waveguide TE₂₁ mode can be suppressed by a cross-type metal plate,which makes mode conversion in bigger caliber circular waveguide possible.Especially,the bending radius is irrelevant to the performance of the mode converter,therefore the radius can be as small as possible.Experimented results show that insertion loss is less than 0.12dB and mode conversion efficiency is higher than 99.5%at8.4GHz.The power capacity is 41.8MW under SF₆ gas,and the bending radius is only 25mm.