开口同轴探头横电磁波模型法测量液体复介电常数

讨论了开口同轴探头技术测量液体复介电常数的理论和实验。在仅考虑同轴线横电磁波(TEM)主模反射波的情况下,用被测液复波数的多项式逼近同轴开口端输入导纳值,简化了复介电常数的求解。以用醇在频率1~18 GHz的导纳测量值求解复介电常数,验证了随多项式项数目增加计算的收敛性。在实验中,为了确定法兰直径最小值和被测液样品最小用量,提出了用被测液边界面与同轴开口面的两项功率比(辐射功率与入射功率比以及无功功率比)作为指标描述边界面电磁场的衰减程度。以1%浓度和3.5%浓度食盐水介电特性测量为例,使用孔径3.20 mm探头,验证了TEM模型法得出的测量结果在0.6~4.5 GHz频率上相比参考值的偏差小于5%。

Transverse electromagnetic model based open ended coaxial probe technique for liquid complex dielectric constant measurement

The theory and the experiment on the open ended coaxial line technique for liquid complex dielectric constant (CDC) measurement are discussed in this paper. In the case that only the transverse electromagnetic (TEM) mode reflection is considered in the coaxial line, the input admittance at the coaxial opening is approximated as a polynomial of the complex wave number in the testing liquid, which simplifies the inversion of the unknown CDC. The solution convergence with an increased number of polynomial terms is validated by de embedding the CDC from the measured admittance data of methanol at 1-18 GHz. In the experiment, to determine the minimum amount of the flange diameter as well as the liquid usage, the power ratio of the radiation to the incidence and the ratio of the imaginary power passes the liquid boundary to that passes the coaxial opening are proposed as indicators to quantify the attenuation of the electromagnetic fields at the boundary. In the dielectric measurement of the 1% and 3.5% saline water, the measurement data obtained from the TEM model by using a probe with 3.20 mm coaxial aperture size are validated and the discrepancies to the reference values are within 5% at 0.6~4.5 GHz.