Research On The New Waveguide Matching Structure

In the analysis and design of passive components of microwave systems,matching two waveguides with different cross-sections is a classical research topic.In order to obtain low reflection transition in a wide bandwidth,single or multi-stage step impedance converters are often used.However,the use of multi-stage impedance converters with different cross-sections,or with continuous tapered cross-sectional dimensions will result in increased length of the matching circuit.In addition,a matching circuit is usually divided into several parts for fabrication,causing fabrication errors and assembling errors being accumulated.It may cause the actual performance of the traditional matching circuit to deviate significantly from the design index.The work of this thesis is a part of the project "systematic research on matching circuits based on complex cross-section transmission lines".Microwave theories,especially analytical theories,play important roles in traditional matching circuit designs.In order to derive formulae easily,one disadvantage of this method is that the crosssectional shapes of the transmission lines forming the matching circuits are usually simple,such as rectangle,circle,etc.Under the guidance of classical microwave theory,with the help of powerful three-dimensional electromagnetic simulation softwares,such as HFSS and CST,the transmission lines with complex cross-sections can be used to form matching circuits,which may open up new design avenues in terms of circuit compactness and matching effects.In this thesis,several new matching circuits,including half-height waveguide step matching and a two-way waveguide power divider,are designed by using one or twostage impedance converters with complex cross-section transmission lines.These circuits will be easy to process,wide-band and compact.The main work of this thesis is as follows:1.The traditional single-stage,two-stage and three-stage waveguide matching circuits are designed.These designs explain the design methods and procedures of the traditional waveguide stepped matching circuits.Compared with these designs,the advantages of our new matching circuits will be displayed.2.The design method of a half height waveguide matching circuit with two-stage impedance converters with complex cross-section transmission lines is studied,including the construction of the model,the choices of the initial structural parameters and the overall optimization process.The shape of the transmission line with complex crosssection is symmetrical in the upper,lower,left and right directions,which is defined by multiple adjacency rectangles(hereinafter referred to as multiple adjacency rectangles).We design,process and test a back-to-back model circuit.The test results are in good agreement with the calculation results.Compared with the traditional two-stage waveguide matching circuit,the new matching circuit has compact structure and good bandwidth performance.3.The design method of quasi plane half height waveguide matching circuit for twostage impedance converter with complex cross-section transmission line is studied(The shape of the transmission line with complex cross section is asymmetric in the left and right directions).The quasi plane structure has the advantages of low manufacturing cost,easy integration and compact structure.4.The design method of a quasi-planar two-way waveguide power divider with a single stage complex cross-section transmission line is studied.The shape of the transmission line with complex cross-section is symmetrical in the left and right directions,which is defined by the multiple adjacent rectangles above which are flush with the input waveguide and the output waveguide.Compared with traditional two-way waveguide power dividers,the length of the new waveguide power divider is shortened and the structure simplified significantly.5.The design method of a half height waveguide matching circuit with single-stage impedance converter with a five-rectangle complex cross-section transmission lines is studied.The shape of the transmission line with complex cross-section is symmetrical in the upper,lower,left and right directions.It is defined by a rectangle in the middle and a total of five partially overlapped rectangles(hereinafter referred to as five rectangles)on each corner of the rectangle.It has the same performance as the traditional two-stage matching circuit,simple structure and short length,and can be easily obtained by traditional CNC machine tools.We design,process and test a back-to-back model circuit.The test results are in good agreement with the calculation results.6.The mechanism of complex cross-section transmission line matching circuit is studied by means of single-stage five rectangle complex cross-section transmission line matching circuit.It is difficult to analyze the matching circuit of transmission line with complex cross-section,so we use numerical simulation to calculate.By calculating the reflection coefficient of each interface in the circuit model of complex section transmission line step,the mechanism of matching circuit of complex section transmission line is analyzed.Finally,the work of this thesis is summarized and the future work is prospected.