Shielded Dual-Mode Microstrip Resonator Measurement of Uniaxial Anisotropy

An improved technique to measure uniaxial anisotropy in planar substrates is described. This technique builds on previous work performed with stripline. The improved approach offers substantially larger bandwidth, lower error, and ease of measurement. An almost complete automation of the entire calibration and measurement extraction process is described. It is also demonstrated that the horizontal (parallel to substrate surface) dielectric constant is less than the vertical dielectric constant for glass fiber weave reinforced substrates for the purposes of microstrip and stripline design. This directly conflicts with bulk measurements of dielectric constant and is believed due to microstrip horizontal electric field concentrating in the substrate surface. This is supported by measurements of a homogeneously ceramic loaded substrate showing the expected relationship. Effects of electromagnetic analysis accuracy, metal roughness, metal thickness, and edge profile (due to etching) are found to be important.