Coaxial Probe for High Temperature Dielectric Characterization

Abstract

Wireless technologies have become an integral part in how we coexist on a daily basis. Specifically, the use of antenna systems plays a huge role in our daily lives. These antenna systems are largely used in some form for most all modern day cellular and radar applications. For proper construction of antenna systems, the electromagnetic properties of the material surrounding the antennas, in particular, the material’s complex permittivity and permeability, must be thoroughly known. It is also important to note that the antennas will be subject to diverse temperature environments, so it is beneficial to know how the antenna material’s electromagnetic properties will change with temperature.

This thesis describes the design and construction of a spring-loaded stainless steel open-ended coaxial probe used to find the electromagnetic properties of materials at elevated temperatures. This research uses network analyzer measurements of the reflection coefficient on an open-ended coaxial sensor in contact with a material. Permittivity is then extracted from the reflection coefficient data by the use of a lumped equivalent circuit model of the sensor’s fields fringing into a sample. Computer verification of the technique is demonstrated, and results for two materials at a frequency range between 0.5 GHz - 1.8 GHz are measured at room temperature, 45 °C, 75 °C, and 100 °C.