Research On Automatic Test System For Measuring Complex Permittivity With Quasi-optical Resonator

In recent years, the microwave and millimeter wave technology has been developed rapidly in various areas. A number of different kinds of dielectric materials whose dielectric parameters have a great influence on the microwave and millimeter wave devices and circuits are used in the microwave and millimeter wave devices and circuits. Therefore knowing the accurate dielectric properties of the dielectric materials becomes more and more important. In the millimeter wave band, about the complex permittivity measurements of low-loss dielectric materials, quasi-optical resonator is very easy to use, has less parasitic mode and high quality factor. In this paper, the design of automatic test system for measuring complex permittivity with quasi-optical resonator are studied.First of all, the basic theory of quasi-optical resonator are analyzed basing on the beam wave theory. Using the MATLAB tool, electric field and energy distributions of Gaussian beam inside the hemispherical quasi-optical resonator are simulated and analyzed. Also the Gaussian beam’s constant phase front at the reflecting surface of a spherical mirror is analyzed. According to the basic theory of quasi-optical resonator, the analysis and design method of hemispherical quasi-optical resonator is given. And the hemispherical quasi-optical resonator which is working at 89 GHz ~ 105 GHz and used to measure the complex permittivity of dielectric materials is designed.Then electromagnetic simulation of hemispherical quasi-optical resonator with coupling aperture is made by use of HFSS. The electric field amplitude distributions of different modes inside the resonator obtained from the simulation are very consistent with analytic results. The magnetic field amplitude distributions and the resonance curves are also given. The resonant frequencies of different modes are very close to theoretical values. The deviations are within 3 MHz.The quasi-optical resonator complex permittivity test system is built based on PNA. The complex permittivity measurement principle and the error sources are studied. And then the test process is defined. The automatic test software for the test system is designed and written with C++ in the Visual Studio 2010 platform. So, controlling the test system, processing the data and calculating the complex permittivity can be done by the test software. Finally completed the analysis and design of automatic test system for measuring complex permittivity with quasi-optical resonator.