Metrology and Testing Center, China Academy of Engineering Physics, Mianyang 621900, China
A shielded cylinder microwave resonant cavity is adopted to realize the precise measurement of permittivity of microwave dielectric ceramics and other kinds of low and medium loss materials, the modematching technique is employed to realize the precise solution of the electromagnetic field in the cavity under dielectricloading condition, and the rigorous relationship between the cavity resonant frequency and material permittivity is obtained. The measurement results of various typical dielectric materials and the test data compared with those of several other methods show that compared with traditional methods, the proposed method achieves higher measurement accuracy with an estimated uncertainty as low as 0.1%; and the permittivity measurement range is extended wider. This method can not only measure the microwave dielectric ceramics with high permittivity, but also measure the low permittivity materials such as crosslinked polystyrene, teflon and etc. Furthermore, as the radiation loss is eliminated in shielded cavity, and the electric current loss in metal surface is restrained, a more accurate quality factor measurement can be realized for low loss materials; the lower limit of the loss angle tangent measurement range can be lower than 1×10-6. This method is suitable for the accurate permittivity measurement of various dielectric materials with the permittivity range of εr=1~100 and above, and the loss angle tangent of tanσ=1×10-3~1×10-6.