Transient analysis of distortion and coupling in lossy coupled microstrips

The transient response of lossy coupled microstrips is studied using the spectral-domain approach (SDA) to rigorously compute the dielectric losses. The dielectric loss coefficient is computed using the SDA with a complex dielectric constant, and results are compared with those obtained by the formula advanced by M.V. Schneider (1969) using a finite-difference approximation for the partial derivative. Transient coupling is formulated in the frequency domain by an even/odd mode approach, showing how differences in either the modal loss coefficients or modal propagation constants can be responsible for coupling between lines. Results for pulse distortion on a semiconductor substrate are presented, showing how losses reduce the signal amplitude without significantly distorting the shape.>