RF material characterization using a large-diameter (76.8 mm) coaxial air line

We report on the development of a 76.84 mm (3.025 in) diameter coaxial air line system whose purpose is to measure the dielectric and magnetic properties of bulk dielectric and ferrite materials over a frequency range of approximately 0.3 - 1500 MHz. We summarize the relative advantages and disadvantages of using large-diameter coaxial air lines for material characterization and we discuss the particular problems associated with calibrating vector network analyzers in this form of transmission line. We also present broadband measurement data on two lossy materials, including a ferrite-loaded polymer and carbon-loaded concrete.