5.5.3 Behavior modeling of geometrically complex components

A circuit module consists of the circuit components and the layout interconnects on the PCB. For the purpose of investigating the coupling to the cavity, depending on the placement of the module inside an enclosure, when the circuit and layout structure are not subject to change, a measurement based behavioral modeling of the module can be performed. The coupling sources of the model are obtained from a single scan, (5.14), and (5.15), even for modules with geometrically complex and nonlinear components, such as, for instance, coils or transformers and active components with no readily available EMC model.

Changing also the module circuit and layout requires component models which can be introduced in a network simulation to obtain the module currents and voltages. A behavior modeling of passive and linear components can be performed by VNA (vector network analyzer) S-parameter measurements. Some network simulation tools support a direct introduction of S-parameter data from VNA measurements, while others require a circuit model which also can be obtained from the S-parameter tables [86], [87], [88]. However, the component pin currents from the network simulation cannot be used to investigate the coupling of the component to an enclosure, because this depends on the geometric distribution of the currents on the component. The coupling current sources

$$J_{s}(x,y)=\sum^{Pn}_{n=1}\left[\alpha_{n}(x,y) I_{n}\right]$$ (5.16)

which describe the coupling to an enclosure are related linearly to the component pin currents $I_{n}$. The linear weighting factors $\alpha_{n}(x,y)$ for the $Pn$ component pin currents can be obtained from $Pn$ scan measurements with different pin current combinations. Circuitry or the layout around the component must be altered to generate different pin currents. Equation (5.16) and the S-parameter table establish together a behavior model of the component, which enables a simulation based design of a circuit module.

C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover