Quasi Optical Cavity Method Of Complex Dielectric Constant Temperature Testing System Research

As multifunctional composite materials, wave-transparent materials are widely applied in the radome of communication systems. As one of the characteristic parameters, complex permittivity shows the ability of the energy storage and the energy loss of the materials. However, the complex permittivity is a function of frequency and temperature. The complex permittivity will change at different frequencies and temperatures. It is of a great significance to obtain the accurate information of the complex permittivities of the materials at different frequencies and temperatures, especially for the design of microwave components and research on the materials. In order to satisfy the requirement, it’s necessary to build a test system which can measure the dielectric constants and losses of the materials at different frequencies and temperatures.First of all, this paper has a further study of the development of the complex permittivity test techniques in variable temperature environment at home and abroad. According to the requirements of the system, and the advantages and drawbacks of different test methods, we finally choose the quasi-optical resonator as the measurement tool. At the same time, we made a study about how to use the quasi-optical resonator in variable temperature measurements.Secondly, a theoretical analysis of the quasi-optical resonator is made; the characteristic parameters of the resonator are also introduced. With the scalar theory, the electric fields in the resonator and the energy distribution on the flat mirror are described. And a analysis is made to the testing theory. According to theoretical analysis, a quasi-optical resonator is designed, which can works at20GHz-40GHz. And an improvement is made to the structure of the resonator to make sure that the resonator can work normally in the environment of1000℃.Furthermore, for connecting the resonator which placed in the vacuum tank with PNA outside, a microwave transition and a hermetic window are designed. Meanwhile, in order to avoid the oxidation of the resonator at a high temperature as well as to protect the safety of the tester, a vacuum tank is made. The induction heating method is introduced in this system, which improve the heating efficiency and rate.Finally, with each subsystem integration, the quasi-optical resonator test system is built up, which can measure the complex permittivities of materials at frequency from20GHz to40GHz, and at the temperature ranges from20℃to1000℃. At the same time, a test software is compiled. With this new system, a series of measurements are made, and the results show that the test system works very well. A rough analysis is made on the system errors. The sources of the errors are obtained. Each error is solved, and the error rang is given.