This article details the impact of non-TEM propagation on a microstrip structure's crosstalk, impedance, and effective dielectric constant. A new onset frequency is defined to quantify where non-TEM dispersion is significant in microstrip transmission lines for high-speed digital applications. The impact of non-TEM dispersion on eye diagrams for digital signals is explored, showing a significant impact from non-TEM dispersion. Using this analysis, guidelines have been defined for when a full-wave simulator must be utilized to simulate a microstrip structure and when a quasi-static simulator provides accurate results at a given data rate. 

This paper was published in Volume 3 of the IEEE Transactions on Signal and Power Integrity. The published paper can be found here.