The introduction of wires into a rectangular enclosure by a multi-mode analogous
transmission line theory has been presented by  and .
The introduction of traces to the parallel-plane cavity field formulations in
Chapter 4 can be achieved by mode decomposition .
The cover plane return current is identified as the parasitic common mode current
depicted in Figure 5.3.
The conductor with number 1 in Figure 5.3 is the trace, the ground plane
is assigned to number 2 and the cover plane to number 3. The partial capacitances between
these conductors are indexed accordingly. A source which drives the traces against the
ground plane will excite both, the differential mode and the common mode currents. The
partial capacitance between the cover and the ground plane is high, due to the
large extent of these planes. A source current that drives the trace is divided by the
capacitances and . Therefore, the excitation of the cavity field
in (4.13) by the trace is expressed by the trace currents
multiplied by the coupling factor
Identification of the cover plane return current as the parasitic common
To extract the
partial capacitances between conductors,
the Laplace equation
for the electrostatic potential has to be solved for
different voltage distributions , .
The surface normal vector at the boundary is . The Smart Analysis Program (SAP),
a FEM based interconnect simulation software from , performs this
partial capacitance extraction automatically. SAP is also capable of automated resistance
and inductance extraction of interconnects.
Figure 5.4 depicts the difference in the electrostatic potential
distribution between a trace with and without cover plane.
C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover
Electrostatic potential with and without the metallic cover plane (qualitative
|(a) Field with cover plane.|| (b) Field without cover plane.