Coupling of inhomogeneous fields into cables over discretized metallic ground planes of finite extent

The numerical computation of field-excited currents on lines (cables) and the corresponding voltages at the terminating impedances is an important task in the area of EMC. If such lines are situated close to transmitting antennas or near metallic structures the inhomogeneity of the exciting field has to be considered carefully. Computing the coupling-in process, it is generally not possible to simply assume plane wave conditions. From well-known reasons cables should be fixed very close to metallic walls and structure parts respectively in order to keep their effective height as small as possible. In numerical models this leads to the requirement that surface areas underneath each line must be subdivided into very small patches, at least perpendicular to the line direction. From computational, physical, and CAD reasons it appears not to be practicable to include lines into the overall mutual electromagnetic interaction process in a numerical model, for example setting up the system matrix in a method of moment (MoM) simulation. It is shown that physically reliable results can be achieved if the output of a MoM field computation is combined with the transmission line (TL) method in a suitable manner.