闭式谐振腔法微波介质陶瓷介电常数测量

Permittivity measurement of microwave dielectric ceramics using shielded-cavity method

采用一种封闭式的圆柱形微波谐振腔,实现了微波介质陶瓷材料以及其他中低损耗材料介电常数的准确测量,通过模式匹配技术实现了介质加载条件下腔内电磁场问题的精确求解,得到了腔体谐振频率与材料介电性能之间的精确关系,对各类典型介质材料的测量结果以及多家比对数据表明,相比于传统方法,该方法的测量准确度更高,可达到0.1%;测量范围更宽,不仅能准确测量高介电常数的微波介质陶瓷,也适用于低介电常数的交联聚苯乙烯、聚四氟乙烯等材料,此外由于闭式腔不存在辐射损耗,金属表面电流损耗也较小,对低损耗材料的Q值测量更加准确,损耗角测量下限达10^(-6)以下。该方法适用于介电常数εr=1~100及以上,损耗角正切tanσ=1×10^(-3)~1×10^(-6)范围内各种材料介电性能的准确测量。

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 mode-matching technique is employed to realize the precise solution of the electromagnetic field in the cavity under dielectric-loading 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 cross-linked 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）.