mom moment internal problem
Hi Adel -- Thanks for carefully considering my comments, and for providing your comments.
I have only a high level understanding of FDTD, so I can not comment on your detailed observations there, but your comments do certainly sound reasonable to me. It is certainly very very clear that limiting one self to just one or two EM tools is often a big mistake.
As for papers on Sonnet de-embedding, the most recent is:
James C. Rautio and Vladimir I. Okhmatovski, "Unification of Double-Delay and SOC Electromagnetic Deembedding," IEEE Transactions on Microwave Theory and Techniques, Vol. 53, No. 9, September 2005, pp 2892 - 2898.
and my original paper is:
J. C. Rautio, "A De-Embedding Algorithm for Electromagnetics," International Journal of Microwave & Millimeter-Wave Computer-Aided Engineering, Vol.1, No. 3, July 1991, pp. 282-287.
I have also solved the problem of de-embedding internal ports exactly. Internal ports are important for SMD, transistors in RFIC, and even in power FET modeling. (Just last Thursday, a very knowledgeable EM researcher told me such a solution is impossible!) The paper is:
James C. Rautio, "Deembedding the Effect of a Local Ground Plane in Electromagnetic Analysis," IEEE Transactions on Microwave Theory and Techniques, Vol. 53, No. 2, February 2005, pp. 770 - 776.
If you want to find more papers on Sonnet, go to
www.sonnetsoftware.com, click on Products->Sonnet Bibliography. You can get the first and third papers from IEEE Xplore, or I can email a pdf of any of them to you, just let me have your email address, or email a request to
info@sonnetsoftware.com.
For terminology, I now always say "shielded" and "unshielded". I talk to a lot of newbies in EM and I have found some confusion when we say "closed" and "open". Sometimes newbies think "closed" means Sonnet does not interface to anything else, when we actually interface to more frameworks than any other tool out there. And on the opposite side, there are several unshielded tools that interface to only one framework, they are most certainly not "open", even though they are unshielded.
I always recommend having at least one shielded and one unshielded tool for planar EM design. For important ("must work the first time") designs, one should analyze the circuit in both, as you have done. Any differences must be understood before going to fabrication. In the case you described, I would guess that the unshielded analysis gave a better match to measurement because you measured it unshielded. If this is the case, then we can conclude that the box sidewalls in your shielded analysis have some effect on the circuit. This means that the fields from your circuit extend out to where the box sidewalls are. This means that if you place other electronic components at that distance, they are likely to couple to your circuit. This is important to realize before fabrication. You do not want to have the system integration people coming after you with baseball bats! Analysis with both shielded and unshielded lets you make corrections before fabrication.