Simple Time-Domain Expressions for Prediction of Crosstalk on Coupled Microstrip Lines

This paper presents an improved variant of timedomain method for predicting crosstalk on parallel-coupled matched terminated microstrip lines. This method derives simple near-end and far-end time-domain crosstalk expressions which are applicable to lossless case with significant harmonic frequency < 1 GHz. The expressions are in polynomial form with geometrical dimensions of the structure and stimulus information as the only required entry parameters. They are simpler as compared to other methods because the difficult-to-determine distributed RLCG electrical parameters of the coupled lines are not needed. A look-up table for the polynomial coefficients is generated for easy application of this technique. The expressions are applicable for board thickness of 4–63 mils, 30–70 Ω line characteristic impedance, 0.5W–4.0W (where W is the line width) inner edge to edge separation, and 3–5 dielectric constant. For significant harmonic frequency > 1 GHz, the effect of both losses and dispersion on the crosstalk levels is accounted for by investigating the gradient of the distorted driving signal. The peak crosstalk levels are then predicted by modifying the time derivative term in the lossless expressions. In addition, the far-end crosstalk is proved to saturate at half of the magnitude of the driving signal entering the active line. The saturation phenomenon is studied from the viewpoint of difference in odd-mode and even-mode propagation velocities.