Resonant open ended coaxial line sensor for measuring complex permittivity

An experimental open ended coaxial line coupled to a 50 ohm source and terminated by a sliding short circuit is used to obtain the complex permittivity of liquids from measurements of short circuit length and return loss. For standard liquids, where the permittivity values are well known, the results obtained at 500 MHz are within a few per cent of the reference values, and demonstrate the potential accuracy of the method.