2011 EMC Directory & Design Guide - Interference Technology

shielding / cables & connectors
Figure 13. FEKO model for an L-shaped single conductor cable over a
ground shape.
shield) and interior (cable bundle) problems only couple
weakly through the transfer impedance. A very similar
approach has been proposed in [17].
The steps of the irradiating case of the analysis method
are shown in Figure 10 and are as follows:
1. Set up the problem geometry and cable analysis request.
The metallic structure will be meshed with triangular
elements. The exterior of the cable path will be included
Num e ric a l S o l u t i o n of C o mpl e x EMC Probl e m s
in the full-wave analysis with the MoM using thin shell
wire segment elements of which the radius, thickness
and material properties are the same as that of the shield.
2. Solve the external MoM system to obtain the shield (wire
segment) exterior current. The MoM solution yields the
total current flowing on the shield exterior.
3. Use the transfer impedance of the shield to convert the
exterior shield current to a distributed voltage source
exciting the multi-conductor transmission line interior
problem.
4. Solve the internal problem using multi-conductor transmission
line circuit analysis.
In a similar manner also the radiating case can be dealt
with.
VALIDATION AND APPLICATION EXAMPLES
Although the techniques presented in this paper can be
applied to complex real-world problems (e.g. cable harness
running in a car), we present in the following rather simple
validation and application examples. These examples have
the advantage that full wave MoM solutions (i.e. discretizing
the cable into MoM wire segments) exist as reference
to compare to the combined MoM/MTL technique, or
measurements / reference results from literature based on
other techniques or other implementations available.
RG58 Coaxial Cable Close to Monopole Antenna
(Irradiation)
A monopole antenna of 10 m height is fed by an input power
of 10 W and is radiating in the neighborhood of an RG58
coaxial cable which forms a U-shaped loop of length 24.24
m. The axis of the cable is assumed to be 10 mm above a PEC
ground with both shield ends short-circuited to ground.
The coaxial core is terminated in 50 Ω to the shield and
the shield transfer impedance is available from a measurement
database. The frequency range extends from 1 MHz
to 35 MHz. Figure 11 shows the configuration setup while
Figure 12 compares the FEKO solution to reference results
[18] for the voltage at the cable end closest to the antenna
(Port 1). The results from [18] are based on a standard MTL
/ MoM combination which is only applicable to cables
Figure 14. Magnitude of the induced current in the load at CCend.
86 interference technology emc Directory & design guide 2011