Design optimization of a high precision microwave complex permittivity instrumentation system for use with high loss liquids

The design of a microwave instrumentation system developed to measure the complex permittivity of high-loss liquids such as water at 9 GHz in the temperature interval from 0°C to 90°C with a 1 σ precision of approximately 0.03% is described. Previous instrumentation allowed a precision of approximately 1% to be attained at 9 GHz. The design is accomplished in a sequence of stages as various unexpected and subtle sources of random and systematic errors are identified and minimized. The statistical precision and repeatability of the measurement data have improved as these error sources are identified and eliminated. The identification and resolution process which allows the improved precision to be achieved is described