eldo_user

Working with S, Y, Z Parameters
Technical Background
where R 1 and R 2 are the reference impedances of ports 1 and 2 respectively.
The S parameters are widely used to characterize high frequency circuits, mainly because they
present no difficulty in measurements while the other parameters are difficult to measure. The
scattering parameters are not unique; they are defined for a given reference impedance for each
port. The reference impedance R 0 is usually 50Ω for all ports to facilitate measurement
(standard coaxial cable has 50Ω characteristic impedance).
In general, an n-port circuit has an n × n scattering matrix of the following form:
Mixed-Mode S Parameters
Bockelman and Eidenstadt 1 developed a theory for combined differential and common
normalized power waves (in terms of even and odd mode). Then it is now possible to
characterize multiport networks at high frequencies, especially such device which are simulated
by common-mode or differential-mode source, by using the extended S parameter definition.
This adaptation, called “mixed-mode S parameter”, addresses differential and common-mode
operation, as well as the conversion between the two modes operation.
According with this new definition, we can see that a two port S parameters form a 4x4 matrix
containing the mixed-mode S parameters (differential-mode, common mode and cross-mode
S parameters). Consider the following differential circuit, each port can support the propagation
of differential-mode and common-mode waves:
1.David E. Bockelman William R. Eisenstadt, “Combined Differential and Common-Mode Scattering
Parameters: Theory and Simulation” July 1995.
Eldo® User's Manual, 15.3 693