高频板材的复介电常数测量方法研究

Research on the measurement of complex permittivity of high-frequency substrate

复介电常数是高频板材最重要的参数之一,准确测量高频板材的介电常数和损耗,对板材的实际应用十分重要。为了获得板材的损耗特性,设计了一种基于微带线的传输线电路,并对长度分别为25.4和127 mm的微带传输线进行仿真、加工和测试,得到DC-20GHz内的回波损耗S11和插入损耗S21,测试数据表明,S11值测试结果在-15 dB以下,且在20 GHz下传输线的插入损耗为24.02 dB/m。通过加工误差分析,电路参数变化50μm时,DC-20GHz内仿真S11max变化可达到6 dB左右。最后结合谐振环法对同一种板材进行测试,得到板材的相对介电常数和损耗角正切。结果表明该方法得到的损耗角正切精确度较高,且在2、10和20 GHz频段下误差小于10%。

Complex permittivity is a crucial parameter for high-frequency substrate.Precise measurement of dielectric constant and loss is essential for the practical application of high-frequency substrate.A transmission line circuit based on microstrip lines was designed to obtain the loss characteristics of the substrate.Microstrip transmission lines of 25.4 and 127 mm in length were simulated,fabricated,and measured to obtain the return loss S11 and insertion loss S21 within DC-20GHz.The measured data indicates that the results of S11 are below-15 dB,and the insertion loss of the transmission line is 24.02 dB/m at 20 GHz.By processing error analysis,the change of simulated S11max within DC-20GHz can reach about 6 dB when circuit parameters changed by 50μm.Finally,the relative dielectric constant and loss tangent of the substrate are obtained by combining the resonant ring method with the same substrate.The results demonstrate that this method yields a high degree of accuracy for the loss tangent,with an error of less than 10%at 2,10 and 20 GHz.