Comparison of three numerical treatments for the open-ended coaxial line sensor

The open-ended coaxial line sensor is commonly used for non-invasive microwave dielectric measurements. A comparison is made between three mathematical treatments that allow the reflection coefficient of the sensor to be derived from the complex permittivity of the material with which it is in contact. It is shown that the discrepancies between values computed by the three methods are much smaller than the predicted measurement uncertainties. Mappings of permittivity contours onto the complex reflection coefficient plane are shown.