Research On Microwave Complex Permittivity Measurement Method Of Multi-size Coaxial Material

In this paper,the complex permittivity test method for coaxial materials is mainly used as the research object.for the measurement of the complex permittivity of coaxial materials with multiple dimensions(different radii)in the project,the network parameter method is mainly used for research.The paper firstly deduces and validates the traditional transmission and reflection method.It gradually expands from the ideal coaxial test fixture to the measurement of different size coaxial materials,due to the discontinuity and standing wave of fixtures,and cause the problem of calibration.Based on the analysis of the two-port network,the ways of using transmission matrix to de-embed the cascaded two-port network and solving the complex permittivity with multiple lengths dielectric are used to solve the problem of non-standard device calibration which caused by the fixture discontinuity,the above method of measuring the permittivity is deduced and verified by simulation.Based on the theory,a set of coaxial material complex permittivity test fixtures were designed for the actual measurement needs in the project.The fixtures were designed in three stages and can be combined into 30 mm and 100 mm length.Using the method of multi-lengths measurement,the calibration procedure of the fixture was omitted,and the test software was designed by using matlab.The complex permittivitys of the PTFE and foamed PTFE materials were measured with the designed fixture.The correctness of theory and simulation was verified.Finally,analysis the error of the measurement results.In order to measure the complex permittivity of coaxial materials with multiple dimensions using the one fixture,a four-port device was designed in this paper.Using the radial-line-based mode converter,and the bragg reflector acts as a coaxial filter.the coaxial material was used as part of the fixture and used.Using the fixture,the S-parameters of the coaxial sample could be measured in real time.After that,the basic theory of the neural network is described.using neural network method,with the amplitude and phase of the simulated S-parameters,which the phase information is compensated to reduce the training error to train the network.then two neural networks are used to build two neural networks to measure the real part of the complex permittivity.The complex permittivity of the coaxial medium was simulated by trained neural network.The results show that the method has certain accuracy and feasibility.For different size coaxial materials,the complex permittivity can be mesured quickly in real time.Finally,the errors in the measurement process were analyzed.