Study Of Complex Permittivity Measurement Of Dielectric Properties Of Layered Materials At Variable Temperature By Single-reflection Method

Microwave materials are widely used in aerospace, satellite communications, radarnavigation and other fields, they are in an extremely complex environment when inprocess of actual application. Complex permittivity is an important parameter ofmicrowave dielectric materials, which changes with temperature and frequency, so howto accurately test complex permittivity of materials in the actual application process isvery important for its applications. A large number of scientists at home and abroad areresearching on how to test the complex permittivity of microwave dielectric materials,most of them are under conditions of normal temperature, but it is not accurate whenunder the condition of high temperature.In this paper, we use the single-reflection method of free space, because of thefollowing advantages: relatively simple physical model and theory of the method, theproduction of the samples is not high, only requires two smooth surfaces. In addition,this method belongs to the non-contact material testing, and testing samples are notdamaged.This paper introduces the common methods of microwave electromagneticparameters and the theory of the single-reflection method of free space, deduces therelationship between complex permittivity of microwave materials and electromagneticparameters, and writes the testing program using the software of Matlab. In addition, wemake some improvement to the traditional single-reflection method: layered materialstesting theory deduced from low temperature to high is applied to test high temperaturematerials; transmitting antenna and receiving antenna are replaced by one spot focusinglens horn antenna, and the signal is separated by a high directivity waveguidedirectional coupler; connect H-plane waveguide Y-junction isolator in the front of thedirectional coupler. All of these can make the whole test system has smaller volume,lower costs, and the most important is to reduce mismatch error source and directionalerror of the testing system greatly, so the calibration of the system only needs to usefrequency response calibration which is owned by the vector network analyzer, it haslargely improved the test precision of complex permittivity of microwave materials. In this paper, we design and fabricate the waveguide directional coupler of X band,simulate X-Band H-Plane Waveguide Y-Junction Circulator with the help of softwareHFSS, design the tablet heating platform, samples of mobile device, fixed bracket ofantenna and samples of materials under test, build the variable temperature test systemof single-reflection method, then use this system to test complex permittivity of thecommon microwave dielectric materials at room temperature to800℃and analyze thesystem errors.