Research On High Power Capacity Compact Bends And Flexible Connection Waveguide Technology

Overmode waveguides are common forms of transmission line used in high power microwave(HPM)transmission and launch systems.Due to the much larger cross-sectional dimensions than standard waveguides,it is able to reduce the maximum electric field strength in the transmission line to the largest extent,thereby avoiding breakdown and increasing power capacity.During the integration process,waveguide bends and soft flexible waveguide connections are essential to meet the complex point-to-point variable propagation requirements of guided electromagnetic waves.The overmode waveguide faces a great challenge in this technical problem compared to conventional standard waveguide bends and flexible waveguide connection devices.According to the theory of orthogonality of waveguide mode transmission,there is no direct energy coupling between the various electromagnetic wave modes in a regular waveguide.However,under engineering conditions such as bending and deformation,the principle of orthogonality no longer holds and the complex coupling process between waveguide modes and parasitic modes occurs,leading to a series of engineering problems such as local field strength spikes,power capacity drops,mismatches at the end of the transmission line and changes in the radiation characteristics of the feed source.With the continuously increasing power capacity requirements of the application system,the waveguide cross-section size continues to increase,how to satisfy the complex point-to-point variable transmission of the guided wave in the process of solving the problem of parasitic mode suppression has become one of the key research directions in the field of high-power microwave transmission technology.The thesis investigates the technology of compacted overmode waveguide bends and flexible connecting waveguides in high power TM₀₁ mode transmission lines,starting from the bending coupling problem of commonly used overmode circular waveguides,constructing mode coupling theories and models,and seeking technical ways to solve the above problems by combining methods such as changing the cross-sectional shape and bending paths on the basis of the analysis of coupled wave theory.The main work and contributions of the thesis are as follows:From the coupled wave theory,the coupled wave equation for an axially curved circular waveguide is investigated and the coupling coefficients between modes in a circular waveguide are derived and presented.Combined with the transmission relation equation of TM₀₁ mode in the bending waveguide,the design and analysis of constant curvature over-mode TM₀₁ mode 90°bend has been carried out by means of the corresponding numerical program.Afterwards,in order to break the constraint relations existing in the constant curvature TM₀₁ bend,numerical program with the bending axis as variable curvature is written by means of a numerical iterative algorithm,and variable curvature TM₀₁ mode 90°bend operating in the X-band is built in the electromagnetic simulation software to verify the accuracy of the numerical program.The structure is more compact than that of the constant curvature,and the transmission efficiency at the central frequency point reaches 99.65%.To further satisfy the requirements of TM₀₁ bend for high power capacity,broadband and compactness,the coupled wave equations for elliptical waveguides are derived based on the variable curvature TM₀₁ mode 90°bend to explore the effect of deformation of the cross-section on the waveguide transmission device.Accurate control of the between-mode coupling is achieved by varying the eccentricity of the elliptic port,and finally designed the variable curvature elliptic TM₀₁ mode 90°bend with maximum bending radius of 435mm,which has the center frequency point of 9.7GHz with a transmission efficiency of 99.82%,the relative bandwidth of 29.8%and power capacity of 6.16GW.In order to investigate the flexible transmitting of the TM₀₁ mode in the transmission line and to compensate for the deviation of the connection position in the high power transmission line,a soft structure was designed using the scheme of mode conversion.According to the structural characteristics of the corrugated waveguide,a section of the flexible waveguide structure with a central frequency point at 9.7 GHz for transmission of the TE₀₁ mode was designed first,and the relationship between its bending angle and transmission efficiency was calculated,as well as the ability to achieve stretching or compression in the axial direction.Finally,a compact TM₀₁-TE₀₁ mode converter with high efficiency was designed for the direct conversion from TM₀₁ to TE₀₁ mode,with a converted efficiency of more than 98%in the range of 8.76 GHz to 10.69 GHz and power capacity of 3.89 GW.Finally,the solution was verified by connecting them.