Gaofeng Guo

BROADBAND MEASUREMENTS OF DIELECTRIC PROPERTIES OF LOW-LOSS MATERIALS AT HIGH TEMPERATURES USING CIRCULAR CAVITY METHOD

We describe a broadband microwave test system that can measure dielectric properties of microwave low-loss materials at high temperatures using circular cavity method. The dielectric constants and loss tangents of samples at different temperatures were calculated from measured shifts of resonant frequencies and unloaded quality factors of the multimode cavity with and without sample. Detailed design and fabrication of the circular cavity capable of working at temperatures up to 1500 ◦ C are discussed. The measurement theory and new calculation method of the radius and length of the cavity at different temperatures are presented. The hardware system was built to measure dielectric properties at wide frequency band from 7 to 18 GHz and over a temperature range from room temperature to 1500 ◦ C. Measurement results of the dielectric properties of quartz samples are given and show a good agreement with the reference values.

A test system for complex permittivity measurements of low-loss materials at high temperatures up to 2000 °C

A microwave test system to measure the complex permittivity of a low-loss material as a function of temperature has been developed, and it is based on the short-circuited line method. The calibration method for the microwave loss and the phase of the waveguide holder which vary with temperature is discussed in detail. Induction heating is employed to shorten the heating and cooling time of the sample and waveguide. The test system was built at 10 GHz and over the temperature range from room temperature to 2000 °C. The feasibility of the system has been verified by measuring the complex permittivity of quartz at high temperatures.

Measurement of Complex Permittivity of Dielectrics at High Temperatures by Using Cylindrical Cavity

Complex permittivity is one of the most important parameters of microwave dielectrics. When the dielectrics work in high temperature environments, the complex permittivity as a function of temperature should be measured while designing dielectrics and applying in microwave devices or radome. A test cavity used at temperature up to 1500degC is designed and fabricated, and the test system for complex permittivity measurement at high temperatures is also built. Some typical samples are measured.