Dielectric Constant Extraction for Microstrip Transmission Lines Based on S-parameter Measurements and Cross-section

In this paper, a new dielectric constant extraction method for the microstrip substrate material is proposed, which is based on measured S-parameter and cross-section analysis of the transmission lines. The calculation process is detailed and application examples are given. The phase constant is calculated from the measured S-parameters. By analyzing the cross-section geometry using a 2D solver, the per-unit-length inductance and capacitance of the air-filled line are obtained. Then using analytical expressions, the dielectric constant of the substrate is extracted from the effective dielectric constant. Comparing to the published method that requires knowing the characteristic impedance of the line, the new method will introduce less error to the extraction procedure and will provide more accurate results.