External field coupling to MTL networks with nonlinear junctions: numerical modeling and experimental validation

The problem of predicting the voltages and currents induced on a printed circuit multiconductor transmission line (MTL) network by an impinging transient plane wave electromagnetic field is considered. The MTL network contains nonlinear circuit elements and test cases with various dielectric substrates are examined. Numerical predictions based on quasi-TEM models of the MTL and modified nodal analysis (MNA) models of the lumped element junctions are compared to experimental results obtained in the time domain using a GTEM cell. As has been done in the past, the effect of the incident plane wave is introduced as forcing functions in the MTL equations. The primary goal of this paper is to quantify the accuracy of the various commonly used quasi-TEM mathematical time-domain models. It is shown that when modeling the forcing function terms, it is important to take into account the perturbation of the incident plane wave due to the dielectric substrate. (The experimental-numerical comparisons herein are shown for the case of end-fire illumination since it best demonstrates this point.) Neglecting the dielectric effect on the incident transient pulse, even for substrates with low dielectric constant, produces poor results.