RS Analyst Model Limitations and Assumptions
As with any mathematical model the RS Analyst model
has limitations. RS Analyst uses transmission line theory to
calculate field-to-wire coupling. The validity of the RS Analyst
transmission line model is subject to the following conditions and
assumptions:
· The are isolated such that the impedance from either
conductor to any ground or other conductive structure is sufficiently large that
its effect may be ignored.
· The
conductors have a constant circular cross section and are uniformly spaced over
the length of the line.
· The
transmission line has uniform characteristic impedance over its length, (i.e.,
 = constant over the length of the conductors).
· Conductor
separation is small compared to the incident field wavelength and the length of
the line. This is not much of a limitation for most electronic
interconnects. For example, a heavily insulated 22-gauge wire may have
insulation about 1 mm thick, yielding a conductor separation of 2 mm, which
corresponds to a free space wavelength of 150 GHz. Conductor spacing is
clearly small compared to the incident field wavelength for most
applications.
· Current and
voltage waveforms induced on the conductors are assumed to propagate in
Transverse Electromagnetic (TEM) mode. When conductor separation is not
small with respect to the incident field wavelength, higher order modes of
propagation may be present and predicted levels at the terminations may not
accurately represent the actual mode of propagation.
· The incident
field is assumed to be a uniform plane wave at the transmission line. The
field impinging on the transmission line therefore has a wave impedance (i.e.,
the ratio of electric field to magnetic field, E/H) of approximately 377 W.
· Any
dielectric surrounding the conductors has insignificant effect on induced
current and voltage levels.
· Circuits at
either end of the conductors are electrically small (i.e. the physical
dimensions of the terminations are much smaller than the incident field
wavelength) and may be considered lumped elements.
· The circuits
at either end of the conductors are assumed to be shielded from the incident
field such that current and voltage induced by the field in the circuit
components and circuit interconnects is insignificant.
· The ground
plane, if present in the circuit under investigation, has infinite extent.
· Conductors over a ground plane are uniformly spaced
above the ground plane over the length of the line.
· For
conductors over a ground plane, the conductor height above ground is small
compared to the incident field wavelength and the length of the line. For
a wire 5 cm above ground, which is common in EMI testing, a quarter-wavelength
occurs at 1.5 GHz. Current and voltage waveforms induced on the leads are
assumed to propagate in TEM mode. When conductor height above ground is
not small with respect to the incident field wavelength, higher order modes of
propagation may be present and predicted levels at the ends of the conductors
may not accurately represent the actual mode of propagation. More:
 Frequency Range
|
