Research On Testing Technology Of Dielectric Parameter Varying Temperature

Microwave dielectric materials are widely used in various equipment in the communications,electronics,medical and household appliances industries.Complex dielectric parameters are one of the most important materials for various microwave applications,and because many equipment,devices and materials need to work in an environment with changing temperature,so how to accurately measure the complex dielectric parameters of materials at different temperatures is an important research topic.The cavity perturbation method is generally regarded as the most accurate method for measuring dielectric parameters,and two assumptions are given out during the derivation process.In order to satisfy the rationality of these two assumptions,it is often considered that the cavity perturbation method can only be used to measure dielectric materials with low dielectric constant,low loss,and small volume.In this paper,several existing methods of measuring the complex dielectric constant and their advantages and disadvantages are analyzed,and then the significance of measuring the complex dielectric parameters of microwave materials at different temperatures is discussed.After that,the relevant basic theories of this paper,including dielectric theory,waveguide theory and resonant cavity theory,are briefly described.Based on this,the basic principle of perturbation method for measuring complex dielectric parameters is expounded.In this paper,the assumption that the electric field of the cavity after perturbation is approximated by the electric field of the cavity in the traditional perturbation theory is discarded.A new physical model considering the electric field change after sample loading is proposed.Taking the square sample as an example,a new perturbation formula is derived.The correctness of the theory is verified by the simulation and experiment.Compared with the formula of the traditional theory,the accuracy and measurement range of the modified formula have been greatly improved.After that,an automatic variable temperature test system is designed and built to measure the complex dielectric parameters of materials at different temperatures.Through the written Labview program,the vector network analyzer is controlled for automatic measurement,and the electric push rod is controlled to push the material regularly through the FPGA program.Then,by unifying the work cycle of each part of the system,the automatic measurement and data collection of complex dielectric parameters of the material can be achieved.The data processing program written by C ++ can be used to process the experimental data in batches to obtain the corresponding relationship between the real part,the imaginary part of complex dielectric parameters and temperature.Finally,using the automatic variable temperature test system designed in this paper to test the ceramic material,the change of the complex dielectric parameters with temperature in the range from room temperature to 560 ? is obtained.The shortcomings in the experimental process are discussed and the error is analyzed.