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 1500οC 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 1500οC. Measurement results of the dielectric properties of quartz samples are given and show a good agreement with the reference values.