A classical way to model lossy TL is to apply the Vector Fitting (VF) technique to theoretical frequency domain impedance expression taking into account both conductor and dielectric losses. The resulting poles and zeros can be implemented by a cascade of unit cells containing a lumped RLC circuit and a transmission line. To get a wideband (40Ghz) model a suitable number of cells and a sub-picosecond simulation time step are required to get accurate results. This VF technique has been applied to a RG58 coaxial cable and the resulting circuit has been simulated in time domain using DWS. The results are then compared at 40Gb/s to those coming from CST Cable Studio up showing a very good agreement with a DWS/CST speedup of about 710X.

1. Copyright Piero Belforte 2015
1
DWS vs CST CABLE STUDIO SIMULATION SPEEDUP
A classical way to model lossy TL is to apply the Vector Fitting (VF) technique to theoretical
frequency domain impedance expression taking into account both conductor and dielectric losses.
The resulting poles and zeros can be implemented by a cascade of unit cells containing a lumped
RLC circuit and a transmission line. To get a wideband (40Ghz) model a suitable number of cells
and a sub-picosecond simulation time step are required to get accurate results. This VF
technique has been applied to a RG58 coaxial cable and the resulting circuit has been simulated in
time domain using DWS. The results are then compared at 40Gb/s to those coming from CST
Cable Studio up showing a very good agreement with a DWS/CST speedup of 720X. An Intel
Quad-Core i7-2630QM 2.00GHz CPU requires 12 min with 4 CPU working in parallel for
CST/CS2014 while about 4 sec with only a single CPU engaged is required by DWS.

2. Copyright Piero Belforte 2015
2
A further 10-100X speedup can be obtained by DWS using a Behavioral Time Model (BTM) instead
of a classical RLC-TL circuit to model the lossy line. This model is built up using PWL (PieceWise
Linear) approximation of S-parameter step reponses of the DUT. A fast convolution wave
algorithm built within DWS allows the user to simulate lossy lines in a fraction of second. The PWL
fitting technique in time domain can be considered as the dual of Vector Fitting in frequency
domain but it is extremely fast, stable and intuitive.