Study On The Measurement Of Complex Permittivity In UWB Resonant Cavity

In order to measure the complex dielectric constant of the solid medium in the 0.5-40 GHz band.In this paper,0.5-40 GHz is split into three bands.A coaxial resonator covers 0.5-5GHz,two cylindrical cavities covering 7-18 GHz and 18-40 GHz respectively.Three cavities are all used with one cavity multi-mode technology.The main work of this paper is as follows:1)There are a large number of models in a sonant cavity and work modes are selected by the analysis of mode distribution.According to the requirements that,frequency of testing should be as much as possible,and should be evenly distributed in the band.The work modes of the cylindrical cavity is calculated,and seven high-order modes,011 TE to 017 TE,are used in the cylindrical cavity.Five modes 001 TEM to 005 TEM,are used in the coaxial resonator.2)Carry out the mode of purification work for the the work mode in cylindrical cavity are high order modes.There are a lot of other modes near to the work modes,if not take the appropriate technical measures,will seriously affect the accuracy of test result.By optimizing the cavity size,the odds and modes of operation are maximized.On the other hand,the difference between the working mode and the degenerate mode field distribution is analyzed.The degenerate mode is suppressed by increasing the back cavity and optimizing the coupling feed position.After the suppression of the working mode,the sweep frequency curve is symmetrical about the resonant frequency.3)Based on the cavity working bandwidth and miscellaneous mold suppression requirements,carried out the feeding and coupling device design.In order to meet the two cylindrical cavity broadband coupling feed,the corresponding frequency band of the double ridge waveguide to the coaxial line converter is designed.7-18 GHz converter standing wave is less than 1.2,18-40 GHz converter standing wave is less than 1.4,to meet the bandwidth requirements.The feed position should be able to energize all operating modes without stimulating or weakening the degenerate mode4)Based on the mode distribution,mode purification and coupling feed,the overall design of the resonator is carried out.For the traditional cylindrical cavity test media placed when the media is not convenient,test cumbersome problem.The cylindrical cavity of the cavity of the cavity to do the innovation and improvement,through the hole in the cavity through the hole to join the slide,in the top of the slide to join the spring.Without affecting the cylindrical cavity field distribution,does not change the original cavity test accuracy circumstances,making the cavity test and join the media test,the two test methods of switching,become fast and simple.This is the innovation of this article.In addition coaxial cavity open end of the radiation too much impact on the test accuracy,in the open end with a gradual structure,so that the diameter of the open end greatly reduced,reducing the cavity radiation to ensure the test accuracy.The cavity is measured by the cavity,and the test result is basically the same as the simulation result.The relative error of the relative dielectric constant test results is less than 5% with the 18-40 GHz cylindrical cavity.