BILINEAR CALIBRATION OF COAXIAL TRANSMISSION REFLECTION CELLS FOR PERMITTIVITY MEASUREMENT OF LOW-LOSS LIQUIDS/

Several parameters describing the quality of petrochemical products ca n be revealed from the permittivity spectrum of the product. This requ ires that the permittivity be measured with high sensitivity, so the c alibration of measurement cells is of great importance. In this work c alibration techniques for the transmission/reflection method for compl ex permittivity determination of low-loss liquids are studied. It is s hown that a bilinear transformation can be used to determine the scatt ering parameters at the reference planes from the measured scattering parameters of a coaxial transmission/reflection cell. The permittivity of a sample in the cell can then be calculated with high precision fr om the reference plane parameters. The de-embedding procedure consists of determining three calibration coefficients by measuring three samp les with known permittivities. Measurements on low-loss liquids and cr ude oils confirm the performance of the calibration procedure. The tec hnique is compared to a simpler calibration method and the choice of c alibration fluids to ensure broad-band measurements is discussed.