Research On New High-order Circular Waveguide Mode Generation Technology

The Gyrotron tube is a typical representative of a high-power millimeter wave source,which has the advantages of high power,long pulse and continuous wave output.Mainly used in millimeter wave radar,communication,high energy physics,controlled thermonuclear fusion,high power microwave weapons and high power electromagnetic heating.The Gyrotron tube usually adopts a high-order whispering-gallery mode or high-order volume mode as the main working mode.Such high-order mode is not convenient for direct use and transmission,and the quasi-optical mode converter can be converted into a low-order easy to use and transmit.The mode,in turn,requires the design of a corresponding high-purity circular-polarized high-order mode exciter capable of simulating the output mode of the Gyrotron tube,and accurately calibrating the performance of the optical mode converter.Therefore,the main work of this thesis is to explore and study the new high-order circular waveguide mode excitation technology,summarize the advantages and disadvantages of traditional quasi-optical mode exciter and waveguide mode exciter,and propose an improved structure based on the basic theory of exciter.A new method of mode coupled excitation is given,and a simulation design model of a new high-order mode exciter in Ku-band and Ka-band is given.To lay the necessary technical foundation for the development of the Gyrotron tube.The main contents of the paper include:A new fin inserted coaxial waveguide mode generator based on beat wave coupling theory,a 6-way fan-shapedTE₁₀ modes in which a coaxial waveguide TEM mode is divided by adding a curved metal fins between the inner and outer conductors of the coaxial waveguide,converted into 6-way fan-shapedTE₂₀ modes,cut off the metal fins,and combine 6-way fan-shapedTE₂₀ modes into a coaxialTE₆₁ mode.Then,the coaxial waveguideTE₆₁ mode is transferred to the circular waveguideTE₆₁ mode.Finally,the circular waveguideTE₆₁ mode is converted into a coaxial waveguideTE₆₂mode by designing a radius-graded corrugated waveguide according to a radius-graded periodic coupled wave theory.This realizes the conversion of the KU-band coaxial TEM mode into a circular waveguideTE₆₂ mode.The highest conversion efficiency of this mode generator is 99.11%,and the highest mode purity is 99.41%.In the aspect of coaxial embedded circular waveguide mode excitation technology based on Bragg resonance,the paper analyzes the main technical difficulties of high-order mode excitation in detail,and proposes a new high-order circular waveguide mode excitation technique with multiple modes of excitation for integrated coaxial mode selection,cavity frequency selection and Bragg resonance conditions.The circularly polarizedTE₁₁ mode is fed by the embedded circular waveguide,and the circularly polarized coaxialTE₅₃ mode is output to the coaxial cavity radiating port through the double-cycle spiral holes or slits distributed on the common wall of the inner and outer cavity according to the Bragg resonance condition.The orthogonal mode expansion method is used to write the MATLAB program to analyze the mode purity of the coaxial port:the coaxial embedded circular waveguide mode generator with small holes coupling,at 30.45GHz,the left-circular polarizationTE₅₃ mode purity is 92.4%,The right rotational component is 0.84%and the generator coupling efficiency is 9.26%.The coaxial embedded circular waveguide mode generator with fine cracks coupling,at30.3GHz,the left-circular polarizedTE₅₃ mode has a purity of 94.26%,the right rotational component is 0.0046%,and the energy coupling efficiency is 96.88%.