Research On Homogeneity Testing Technology Of Microwave Performance Of Bar Dielectric Material

The dielectric material is an important medium for electromagnetic wave propagation,of which the microwave performance is the key index to evaluate the microwave transmission characteristics.Homogeneity of the dielectric material's microwave performance is an important indexe for material qualification evaluation.Inaccuracy of the measuremen maybe make a great negative influence on the performance of devices,systems and the whole machine,and even prevents the machine from working normally.The two characterization parameters of the material's microwave properties are permittivity and dielectric loss,which belong to the intrinsic parameters of material.The existing measurement methods and systems of the dielectric parameter homogeneity are developed on basis of the traditional measurement methods.The minimum measurement interval is limited by the structure size of the test fixture.This results in the inability to obtain uniformity distribution performance with higher measurement resolution.The existing attenuation measurement methods and systems with the low measurement resolution and the inaccurate simulation of the electric field environment cause the greater measurement errors.In view of the above problems,this paper studies the characterization of microwave performance and uniformity distribution of dielectric materials from three aspects:theoretical research,measurement modeling and system design.The paper mainly focuses on the measurement and analysis of homogeneity distribution of complex permittivity and attenuation of dielectric materials.Based on the analysis of the existing test methods and systems,the adjacent sub-sample comparison model based on the perturbation method is proposed for the complex permittivity distribution measurement.At the same time,mode matching measurement model for the segmented sample is proposed to further improve the measurement resolution.In addition,the eccentricity measurement model is improved based on the mode matching field analysis.A cascaded multi-cavity is developed and used as the homogeneity measurement sensor.The measurement system and software are designed for the automatic measurement.For the attenuation distribution measurement,an equivalent calculation model of coupling parallel strips and UWB impedance gradient structure of parallel strips are proposed to improve the attenuation measurement interval resolution.The parallel strips fixture and the corresponding calibrator are developed.The automatic measurement is realized by integrating system and programming test software.The main research contents and innovations are summarized as follows:1.The significance of the research on the performance homogeneity of the dielectric materials is clearly described.The relevant research on the measurement of the homogeneity distribution of the dielectric materials at home and abroad have been carefully consulted and analyzed.The difficulties and problems existing in the measurement methods and systems are summarized.To solve the related problems,this paper puts forward the new research ideas,which aims to realize the homogeneity measurement of three microwave parameters of dielectric materials.2.The resonant mode and field expression of TM_0n0 cylindrical cavity are studied and analyzed,and two classical measurement models:perturbation method and mode matching method are introduced.Secondly,the reflection characteristics and field distribution of parallel strips are analyzed.Two classical physical models of microwave network parameter method and equivalent circuit method are introduced.The above analysis provides theoretical support for the subsequent homogeneity distribution measurement.Based on the above theory analysis,TM cylindrical cavity and parallel strips are proposed as the test fixture.3.Based on the perturbation method,the adjacent permittivity comparison measurement model is established,and the two-section measurement method is proposed.Compared with the traditional resonant cavity measurement,the measurement interval resolution is doubled.The mode matching model with segmented sample is established to calculate permittivity of the sample partially filled in the cavity and with greater inhomogeneity.The measurement method of samples with N-section in the cavity is put forward innovatively,which improves the resolution of permittivity measurement interval by N times.In addition,to decrease the measurement error caused by the sample eccentricity,an eccentricity correction model,which includes postion obtention by the visual measurement,filed calculation by mode matching,and permittivity calculation by perturbation theory,is proposed.This model further improves the model of distribution measurement.A cascaded multi-cavity sensor and measurement platform are developed.The system integration and automatic test software are finished.4.Based on the approximate field analysis of parallel strips,the parallel strips measurement model with a middle hole and side hole is established.In the middle hole model,the parallel strips is regarded as two coupling parallel strips.The attenuation calculation expression of the parallel strips with the middle hole is deduced by using the field analysis of the coupled parallel strips and the odd and even mode theory.Based on the analysis of edge equivalent capacitance,a parallel strips calculation model with the side hole is proposed.In order to realize the impedance gradient from parallel strips to the coaxial probe,a new UWB impedance matching structure and the corresponding calibration device for parallel strips are designed.After integrating and programming automatic test software,the measurement of attenuation uniformity distribution is realized.5.The measurement results of complex permittivity and attenuation uniformity are analyzed in detail.The measurement accuracy of complex permittivity is verified by comparing the measurement results of the standard sample with the data of other countries.The effectiveness and higher resolution of attenuation test is verified by comparing the results with double ridge waveguide.The system error and random error are analyzed,and the main test error sources are defined.The measurement results and errors show:As for the permittivity measurement system,measurement frequency:2GHz³0GHz,measurement permittivity:1¹0,permittivity error:|??_r'/?_r'|?2%,loss tangent:1.0e^-41.0e^-3,loss error:|?tan?_?|?10%tan?_?+1.0e^-4.As for the attenuation measurement system,measurement frequency:6GHz⁴0GHz,measurement interval resolution:<1mm,measurement attenuation:0.1dB/mm⁵dB/mm,measurement stability:±0.01dB/mm.The two systems have been applied in CETC 12^th Institute and provided powerful technical supports for the development and application of the dielectric rod in TWT.