Full field and quasi-TEM time domain numerical analysis of coupled microstrip circuits

Both full field and quasi-TEM time domain analyses of various coupled microstrip line configurations are presented and compared. The full field analysis as well as the quasi-TEM analysis are performed using (different) finite difference time domain algorithms. The first solves Maxwell´s equations and the latter solves the multiconductor transmission line (MTL) equations. The capacitance and inductance matrices required for the MTL solution are determined using a previously published electrostatic Green´s function technique. The coupled microstrip lines are terminated with resistive loads with values close to the characteristic impedances of the lines. Time domain results show that the quasi-TEM analysis is very qualitatively similar but not the same as the full field analysis. The quasi-TEM analysis requires much less computer resources and may be sufficient for some cases. For more complicated structures only a full field analysis can show some detailed coupling phenomena.