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

The authors describe the evolution of the design for a microwave instrumentation system which has been 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 1σ precision of approximately 0.03%. Previous instrumentation had enabled a precision of approximately 1% to be attained at 9 GHz. The evolution of the design has been accomplished in a sequence of stages as various unexpected and subtle sources of errors have been identified and minimized. The statistical precision and repeatability of the measurement data have improved as these error sources have been identified and eliminated. The identification and resolution process which has enabled the improved precision to be achieved is described