Material Measurements Using VNA-Based Material Characterization Kits Subject to Thru-Reflect-Line Calibration

This article presents a study of different calibration techniques for vector network analyzer -based material measurements using commercially available material characterization kits (MCKs). Such MCKs are designed for fast broadband material characterization at millimeter-wave and terahertz frequencies and are based on gated-reflect-line calibration for removal of errors associated with the fixture. In this article, we have applied thru-reflect-line (TRL) calibration to the MCKs, yielding robust S-parameters that are used to calculate the relative permittivity and loss tangent of materials. Two different types of line standards, i.e., custom machined corrugated lines and air lines (a quarter-wave air gap between the ports of the MCKs), were employed to produce the desired phase shift. Both types of standard produced similar results. These investigations were carried out on three types of low-loss dielectric material, using MCKs operating at two selected waveguides bands within the range 140-750 GHz. The same samples were measured using time-domain spectroscopy (TDS) for comparison. The extracted relative permittivities and loss tangents using MCKs with TRL calibration and TDS are compared against literature values. Good agreement is achieved.