Hi Timothy, Though, this topic was discussed here multiple times, I think it worth to revisit it from time to time, considering the recent developments in this area. Here are my takes on it. First of all, you have to distinguish two S-parameters use cases during the system-level analysis. S-parameters may be used directly in discrete or tabulated form with possible interpolation in frequency domain and with some IFFT or convolution algorithms in time domain. Alternatively, S-parameters can be converted into rational compact macro-model both for frequency and time-domain analysis. The rational macro-models usually provide superior accuracy and performance both in time and frequency domain analyses and ideally should be used as the models of multiport structures (in form of broad-band SPICE models for instance) whenever possible instead of the Touchstone tabulated models. Considering setting the bandwidth for electromagnetic analysis, the low frequency should be below the transition to skin-effect (lower MHz for PCBs) to allow safe extrapolation to DC. Note, that this is not possible with tools that use SIBC to simulate the skin-effect. Typically, the high frequency should be defined by the required resolution in time-domain (1/2tr). Though that may be not possible due to propagating high-order modes and this frequency may be set to a smaller value if your solver builds rational compact macro-model with the delay extraction - it technically provides the extrapolation. The resolution and spacing are very important for IFFT and convolution algorithms and were discussed here before, but not that important to build rational macro-models, as soon as there are 3-4 frequency points for each resonance. Considering the quality analysis and restoration, I would recommend to study this paper: P. Triverio, S. Grivet-Talocia, M.S. Nakhla, F.G. Canavero, R. Achar, Stability, causality, and passivity in electrical interconnect models, IEEE Trans. on Adv. Pack., v. 30, N4, p. 795-808. The best way to compare the original and "restored" S-parameters is to plot and compare them in frequency domain (phase and magnitude). The original and restored S-parameters are typically almost identical in case of small violations and visually different in case of large violations. The data should be discarded in the later case as rightly pointed out in the cited paper. Considering the quality of S-parameters from the electromagnetic analysis, violation of reciprocity and passivity are relatively rare (only in case of algorithm failure). Properties of S-parameters due to geometric symmetry can be violated with non-symmetric meshing. The causality is often the issue due to non-causal models of dielectrics and conductors used in some electromagnetic analysis tools. This is not a problem for narrow-band microwave applications, but a problem for the broad-band digital application. Causality of such S-parameters can be restored by building the rational macro-model, but it does not actually improve the quality of the model and the model typically has to be discarded and rebuilt with the broad-band causal models both for dielectrics and conductors. Best regards, Yuriy Shlepnev www.simberian.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Timothy Coyle Sent: Tuesday, February 24, 2009 9:52 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Preparing S-Parameters for Simulation Hi, I am working on a tutorial for the next issue of XrossTalk Magazine about getting S-Parameter models ready for simulation. I see a lot of S-Parameter models from lab measurements and simulation tools that have a lot of quality issues (causality and passivity) and have to do a lot of clean up to make them suitable for simulation. I have my own bag of tricks I use as well as some good books on S-Parameter theory and application notes but I would like to hear from other people what their approaches are or some good resources. For some particular specifics review the list below: . What considerations should go into setting up a simulation tool to extract an S-Parameter model? (bandwidth to be used, number of points, importance of linear spacing of points, starting at DC, etc) . A lot of tools will automatically "fix" causal and passivity issues or enforce them. What's the pros and cons for this? What do engineers need to look out for when they do this? . What's the best way to clean up a lab measured S-Parameter model with poor resolution? . What type of quality checks should you perform on an S-Parameter model before simulating? (what do you look for in the S21 plots, do you use smith charts, ect?) Thanks for any and all suggestions and links. Best, Timothy Coyle Editor In Chief XrossTalk Magazine 405 Western Ave #430 South Portland, ME 04106 Tel: 617.297.2566 Fax: 207.510.8099 Email: tim@xxxxxxxxxxxxxxxx http://www.xrosstalkmag.com <http://www.xrosstalkmag.com/> ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu