Researchrs On Complex Permittivity Measurement Of Dielectric Materials At Millimeter Wavelengths

With the continuous development of millimeter-wave terahertz spectrum resources,dielectric materials are widely applied in antennas and circuit systems at millimeter-wave band,and the electromagnetic properties of the materials would determine the performance of the system.It is important for system design to get the complex permittivity of dielectric materials accurately.The application of traditional transmission line and closed resonant cavity method to measure complex permittivity at millimeter-wave band is greatly restricted due to the disadvantages of large loss,difficult processing,and low measurement accuracy.Therefore,realizing the complex permittivity measurement of the dielectric materials at millimeter-wave band has very important theoretical and engineering significance.In this thesis,the quasi-optical open-cavity measurement technology is selected and the complex permittivity measurement system of the quasi-optical resonator at V band and W band is constructed.Moreover,according to the characteristics of the SIW traveling-wave slot array antenna,a method for measuring the permittivity of the PCB substrate at W band is proposed.The quasi-optical resonant cavity has the advantages of high Q value,easy processing,convenient tuning,good single-mode performance,extremely wide frequency band,convenient medium selection,and easy control of medium temperature.Our research group has the design experience of quasi-optical resonator at Ka band and W Band.On this basis,quasi-optical resonators at V band and W band are designed and the resonant state of the cavity and the loading cavity can be calculated by simulation software(CST).So that dielectric constant measurement simulation experiment are completed.By comparing the calculated value with the preset value,it is found that when the dielectric constant value is less than 4,the dielectric constant measurement error at V band would be less than 0.5%;when the dielectric constant value is less than 3,the measurement error of at W band would be less than 0.06%.The feasibility and accuracy of the quasi-optical resonant cavity to achieve complex permittivity are verified at millimeter wave band.At present,the measurement system has been designed and processed,and physical measurement will be carried out in the future to verify the performance of the measurement system.Substrate-integrated waveguide can not only be processed by traditional PCB technology with low cost,but also have the advantages of low loss and high Q value.In recent years,SIW has gradually begun to be applied to the field of permittivity measurement.The main beam direction angle of the SIW traveling-wave slot array antenna will be different with the different dielectric constant values of the substrate.According to this feature,the dielectric constant value of the dielectric material can be calculated by measuring the antenna direction angle.This thesis designs and processes three antennas whose center frequency at93 GHz through simulation software(HFSS).The Rogers R/T 5880 is selected as the substrate medium and the feasibility of the method is verified through physical measurements.Under the requirement of accurately measuring the direction angle of the main beam,the method of mirror antenna is applied to ensure the accuracy of the measurement as much as possible.The calculated values of the measured dielectric constant are 2.2217?2.2325,the average value is 2.2260 and the fluctuation rate is 0.49%.It is the first time to complete the work of measuring the dielectric constant using a traveling wave antenna at millimeter wave band.