Coupled Stripline Benchmark
Many users are interested in the accuracy of EM simulations for loosely coupled transmission lines. Users are particularly worried about the dynamic range or noise floor of their simulation. Since infinitely thin coupled stripline has a known exact solution, it can be used to quantify EM simulation errors or measurement errors.
The Excel spreadsheet, csl.xls, which may be found in the Sonnet example files accessible through the help menu of any Sonnet application, uses the long-known exact solution for lossless infinitely thin stripline. Solutions for both coupled and single stripline are included, but this discussion deals mainly with the coupled stripline solution. See Chapter 26, "Accuracy Benchmarking" in the Sonnet User's Guide for a discussion of the single stripline standard benchmark. You may access the manuals in PDF format through the Sonnet task bar.
The solution is calculated to +/- 3e-6%. Simply input the parameters of the single or coupled stripline you are using as a benchmark and the exact S-parameters of the structure are then calculated. Compare these results with the measurement or analysis and you can determine the exact error.
When pushing EM software to its limits, it is valuable to have a way to benchmark the software to obtain confidence in the software's accuracy. Therefore, this spreadsheet could be used to verify the accuracy of em at extreme limits, such as ultra-high dielectric constants, extremely thick or thin dielectrics, extremely loose coupling, etc.
As you probably already know, Sonnet has invested a lot of time into quantifying the errors in our analysis engine, especially errors due to subsectioning. The Sonnet User's Guide has a chapter (''Accuracy Benchmarking'') dedicated to the single stripline benchmark. It shows how you can extend the technique to determine the errors in transmission lines which do not have an exact solution. The end of the chapter also discusses how to correct for the error in the analysis. The chapter is worth reading. (Note: See also our on-line Benchmarking EM Software document.)
Sonnet also has a PowerPoint slide presentation which uses Richardson extrapolation of a coupled stripline to determine the noise floor of the Sonnet analysis engine. This presentation is available upon request.
