The subject of this dissertation is the development of an efficient simulation method for the electromagnetic emission from printed circuit boards (PCB), which are situated under a metallic cover at an electrically short distance. Examples of such configurations are automotive control devices, where the PCBs are often parallel to a metallic enclosure cover, mobile devices, like cell phones with metallic shields or parallel PCBs, slim DVD, enclosures and devices with PCBs parallel to a metallic cooling device.

An investigation of memory- and simulation time efforts of several numerical methods for the simulation of the emissions from complex PCBs in the frequency range from a few kHz to several GHz reveals that three-dimensional full wave solutions are extremely costly in the mid-term. Emission simulations have to consider integrated devices, which together with their enclosure are sources of emission, and external devices, which interact with the device under investigation by connectors and cables. Both increase the complexity problem of the simulation, especially, if numerous simulations are necessary in a computer aided design (CAD) optimization process.

In this work the emission mechanisms, such as conducted emission, direct radiation of transmission line loops, or common mode radiation of components on the PCB and their model description in the literature are investigated in a first step. From these mechanisms based models, an efficient simulation method is developed. Modeling the mechanisms leads to a significant simplification of the numerical problem. The assignment of the models to source and coupling path enables a simulation domain separation and an efficient optimization. An example for the advantage of assigning this model to a source is the common mode inductance of a component on the PCB. This inductance is assigned to the component and independent of any attached cable on the PCB, which acts as the antenna.

The components on the PCB and the PCB interconnection structures excite an electromagnetic field between the PCB ground plane and the metallic cover. Electromagnetic emission is caused by this field, which couples to the external environment at the slots between the ground plane and the cover plane. The parallel plane field is described by a cavity model, which has frequently been used in the literature for the modeling of power plane fields. This cavity model is based on a two-dimensional Helmholtz equation, which can efficiently be solved by established numerical and analytical methods. This work shows that the excitations of the cavity field by the sources on the PCB can be described by an analytical expression. For the description of the emission from the parallel plane slots, a new approach of domain decomposition with port interfaces based on the equivalent source theorem is presented. With the interface ports of the cavity model and the analytical description of the excitation, a common mode coupling path model from the sources on the PCB to the interface slots is established. This coupling path model is independent of the sources on the PCB and of the external environment of the device. It is valid for every kind of source, independent of whether it couples magnetically or electrically. For magnetic coupling sources below the first resonance, there is a direct relation to the common mode inductivity, which has been used in the literature to model the common mode emission from integrated circuits (ICs) and traces on a PCB. The model in this work is valid as long as the separation distance from the cover to the PCB ground plane is electrically small. This condition holds in most applications up to high cavity modes. In the literature the common mode coupling from ICs is modeled by mTEM measurements or by field scan methods. For direct IC radiation, the literature describes a modeling approach with dipoles, based on simulated IC currents. The measurement modeling methods need a prototype device. The dipole model has no explicit relationship to the common mode coupling mechanism and needs therefore three-dimensional full wave simulation to consider the enclosure of a device. The analytical method for the description of the excitation presented here enables a modeling based on the geometry of the IC package and the conducted currents, which can be obtained with network simulation. The main advantages of the method presented here are the explicit formulation of the common mode coupling and the fully simulation based modeling, without any measurements. This enables an efficient modeling of the common mode coupling from ICs to the enclosure by analytical and powerful numerical (i.e. FEM) methods.

For initial information about the emission from an enclosure with a slot, a fully analytical model is used to calculate the free space radiation. The model applies a new method for considering the radiation loss in the calculation of the cavity field. The radiation loss is considered by an admittance network, connected to interface ports at the slot of the enclosure. This admittance network is expressed by an analytical far field solution.

In addition to this fully analytical method, the work presents various implementation options for the developed simulation method, which can be used for the optimization and efficient prediction of the emissions of complex devices by simulation.

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