Metrology and modelling of high frequency probes

Badenhorst, J. (2008-03)

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008.


This study investigates high frequency probes through good metrology and computation software such as CST. A factor that can strongly influence the accuracy of measurements, is common mode (CM) current. Therefore, the main focus of this project was the CM current on the outside of an SMA, flanged, probe used for measuring material properties. In the course of the investigation, a clamp-on CM current probe (CP) was calibrated using a CST model and good measurements. This calibration data indicated that the CP was invasive on the measurement setup and could not deliver the accuracy required for the CM current measurement. In light of this, a second method was implemented where the material probe was placed within a cylindrical shield. A cavity was formed between the probe and the walls of the shield in which the electric fields could be simulated and measured. These field measurements allowed measurements to be conducted in both the time- (TD) and frequency-domain (FD). For the TD measurements, a sampling oscilloscope was used. As the basic principle of a sampling oscilloscope differs from its real-time counterpart, this principle, as well as the systematic errors associated with these devices, was explored. The results of the final measurements indicated that the TD results were within an acceptable range of both the FD results, measured on the VNA, and the results predicted by CST. This study shows that CST can be used to simulate complex measurement setups and deliver reliable results in cases where an accurate measurement cannot be guaranteed.

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