The two-dimensional Helmholtz equation was utilized to efficiently model the cavity field between the power- and groundplane of a PCB for the purpose of power integrity analysis [42][43]. Traces were introduced into the cavity field model by mode decomposition for signal integrity and power integrity simulations on PCB level [44].

This work develops a model for the field between the ground plane of a PCB and a parallel metallic cover based on this two-dimensional Helmholtz equation. Traces on the PCB are efficiently introduced into the cavity model by an analytical formulation without mode decomposition. The introduction contains explicit information of the common mode coupling. The thereby obtained insight enables the reduction of device optimization only on relevant parameters. The common mode inductance of a trace above a ground plane without a metallic enclosure derived by [36] and [37] depends on a factor d/W (d...trace height above the ground plane, W... ground plane width). It is shown in this work that the same dependence can be obtained from the cavity model and the analytical trace factor. Therefore, the coupling effect, described by the cavity model, is the same as that of a trace above a ground plane. Powerful analytical and numerical methods are presented for the solution of the two-dimensional Helmholtz equation. The external environment of the enclosure can be simulated with another established simulation program, according to a new domain separation method, as mentioned previously. The next section describes an additional application of the proposed cavity model for fast predesign investigations.