Recent interest in anisotropic metamaterials and devices made from these materials has increased the need for improved RF material characterization. Practical methods for measuring these types of materials at low frequencies have been limited to fully or partially-filled VHF waveguides, which are large, expensive, and slow. This paper presents a new method for VHF & UHF characterization by simplifying the process of obtaining intrinsic properties for inhomogeneous and anisotropic dielectric materials. The fixture combines low-frequency capacitance and high-frequency coaxial airline concepts to measure cube-shaped specimens and is termed an “RF Capacitor”.
Furthermore, a new inversion technique is introduced, based on a full-wave, finite difference time domain (FDTD) solver to exactly model the measurement geometry. This FDTD solver is applied in a novel way to enable the inversion of frequency-dependent dielectric properties within seconds. This paper presents the fixture design and calibration method along with example measurements of isotropic and anisotropic dielectric materials. Three-inch (76 mm) cube specimens are measured and the bulk dielectric properties in the three principal directions are determined by measuring the same specimen in three different orientations within the fixture. Finally, calculations are presented to show the relative accuracy of this method against some probable uncertainty sources.
