An Empirical Modeling of Far-End Crosstalk and Insertion Loss in Microstrip Lines

Abstract

The difference in the dielectric permittivity of the different dielectric layers (including air) surrounding the microstrip is one of the major contributors to the far-end crosstalk (FEXT) in microstrip lines. The dielectric of the microstrip in printed circuit boards (PCBs) fabrication usually consists of two layers: the solder mask layer and the substrate layer. The characterization of the relative permittivity ( ${\boldsymbol{\varepsilon }}_{\boldsymbol{r}}$ ) and dielectric dissipation factor (tan δ ) for the dielectric layers of the microstrip are important parameters for board-level electronic system designs. In addition, the foil surface roughness cannot be ignored for the conductor loss modeling. In this work, an extraction method with high accuracy is proposed to characterize the dielectric material and foil surface roughness properties from the measured S-parameters with known cross-sectional geometry up to 20 GHz. With the extracted properties, the FEXT and insertion loss of the microstrip can be estimated more accurately, providing design guidelines for PCB design and the material selection of the microstrip.