Comparison of Reflection and Transmission Method and Metal Back Method Measurement of Dielectric properties of transformer oil using free space microwave measurement system in 8 - 12 GHz frequency range

Nondestructive, non-contact and real time evaluation of dielectric properties of low-loss liquids is important for applications such as service-aged transformer oil, biomedical, remote sensing and design of radar absorbing material. Free-space methods (which are nondestructive and non-contact) were developed a measurement of dielectric properties of transformer oil at microwave frequencies. Transmission and Reflection method and Metal Back Method are developed for measurements using free space microwave measurement system (FSMM). FSMM system consists of spot focusing horn lens antennas, mode transitions, coaxial cables and vector network analyzer (VNA). Dielectric constants and loss factors were measured for new transformer oil. It is observed that metal-back method is suitable for dielectric measurement of transformer oil compared to Transmission and Reflection method.