低损耗材料微波介电性能测试中识别TE01d模式的新方法

工作于TE01d模式的金属谐振腔法是评价低损耗材料微波介电性能的通用方法.微波介质谐振器均为多模式谐振器,故正确识别TE01d模式是微波介电测试的基础.TE01d模式的识别可通过预测谐振频率及其随谐振器尺寸的变化、根据激励条件排除寄生模式等手段实现,但已有方法存在复杂、易识别错误等缺点.为此,本文发展了一种准确识别TE01d模式的简单方法.这种方法引入了介电性能已知的低损耗参考试样,通过测试金属谐振腔中只放置参考试样及同时放置参考试样和待测试样时TE01d模式的谐振频率,利用有限单元分析计算出待测试样的粗略介电常数,并进一步预测只放置待测试样时TE01d模式的谐振频率.此谐振频率的预测值与测试结果相差1%以内,因此很容易将TE01d模式与其他寄生模式区分开,进而实现TE01d模式的准确识别.

A new method for identifying TE01d mode during microwave dielectric measurements of low-loss materials

The metal resonant cavity method working with TE01d mode is a universal method for evaluating the microwave dielectric properties of low-loss materials.All the microwave dielectric resonators are multi-mode resonators,so the correct identification of TE01d mode is the basis for the microwave dielectric measurements.The TE01d mode can be identified by predicting the resonant frequency and its variation with resonator size,expelling the spurious modes according to the exciting conditions,etc.,while these methods are relatively complex and sometimes unreliable.In the present work,a simple method for accurately identifying the TE01d mode is developed.A low-loss reference sample with known dielectric properties is introduced and placed in the cavity for the first step,and the to-be-measured sample is placed on the reference sample for the second step.The rough permittivity of the to-be-measured sample can be calculated from the TE01d-mode resonant frequencies in the two steps through the finite element analysis,and is used to predict the resonant frequency for TE01d mode when only the to-be-measured sample is placed in the cavity.The difference between the predicted and measured TE01d-mode resonant frequencies for the to-be-measured sample is less than 1%,so that the TE01d mode can be easily distinguished from the spurious modes and accurately identified.