A permittivity measurement system for high frequency laboratories
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006.
The open-ended coaxial probe is revisited as a broadband measurement system for general high frequency permittivity measurements. Three coaxial probes were developed that are suited for the measurement of both liquids and solids. The components of a permittivity measurement system were investigated and improvements were made to the coaxial probe where needed. This includes the development of a full wave code with great calculation time improvements without sacrificing accuracy. This code allows measurements to be performed in a high frequency laboratory and the permittivity extracted without any mentionable delay. A capacitance model that better describes the impedance of an open-ended coaxial line is also suggested that can be used for real-time permittivity extraction over a limited frequency range. Calibration formed a vital part of the project and great time was spent developing a TRL and a SOLT calibration set for the coaxial probe geometry. The combination of the TRL and SOLT standards also allows measurement of the residual errors after calibration and is used in an uncertainty analysis of the extracted permittivity. Well known materials such as PTFE, PVC, methanol and water were measured to test the probes. The measured dielectric constants are all within 3% of values quoted in literature. The loss term of the samples are also in good agreement with the expected values.