Precision Microwave Complex Permittivity Measurements of High Loss Liquids

Abstract

This paper reviews the various experimental methods that have been used to measure the real (permittivity ε') and imaginary (dielectric loss ε″) components of the complex permittivity of high loss liquids at microwave frequencies. These methods can be classified as being in either the frequency- or the time-domain. The sample cells used are either reflection or transmission and of either fixed- or variable- length. The achievable accuracy at 9 GHz has been 1% until recently when a new instrumentation system has been described which makes it possible to attain a 1 σ precision of ∼0.01%. This system uses either a variable-length transmission or reflection sample cell and consists of a dual channel, double superheterodyne signal processing system which coherently transfers the phase and amplitude information from 9 GHz to 60 MHz and then to 1 kHz. The amplitude and phase can be measured to 2% at 9 GHz but to about 0.001 dB and 0.01 ° at 1 kHz. The details of this system and the factors that limit the precision are discussed and the role of systematic errors is examined.