Merrick, You have started very interesting thread and have got a lot of useful recommendations. I enjoyed reading it and just wanted to summarize a few things. The problem of splitting a reciprocal, balanced symmetrical multiport into two parts cannot be solved in general - it is un-determined inverse problem. Let me explain. S-matrix of a two-port (one-conductor line segment with connectors for instance) have 2 independent complex parameters S11=S22 and S12=S21. If we want to split it in the middle, the S-parameters of each half are identical, but there are 3 independent parameters to find due to the un-symmetry of each half - SA11, SA12=SA21 and SA22. If we convert S into T matrix and SA into TA, then the following matrix equation arise: T=TA*P*TA^-1*P where P is the permutation matrix (to interchange b and a) and TA is the matrix with 3 unknowns. Only 2 elements of T are independent due to symmetry and reciprocity and 3 elements in TA due to the reciprocity. As you can see this is not a square root of matrix problem - it becomes such only if both halves of the multiport are also symmetrical (T=TA*TA in this case, or two identical line segments without transitions). Otherwise it is a problem with only 2 independent non-linear equations and 3 unknowns. One way to solve it is to add more equations - measure S-parameters for lines with different lengths for instance. The problem is very sensitive to noise and physical non-identity of the test fixtures. In addition the problem is solvable with frequency-dependent uncertainty in the characteristic or in the normalization impedance of the port in the middle (you are lucky if it is close to 50). There must be an experiment with a resistive element to remove the impedance uncertainty (there was a theorem about that in some very old books on microwave theory). The alternative approach based on guessed equivalent circuit with a line in the middle and some circuit modeling the transitions is as good as the line model that it is based upon. The line model in such approach should be verified over the frequency band of interest (include frequency-dependent effects of dielectric, conductor and high-frequency dispersion). Otherwise the error is just hidden into the transition circuits and propagate further into the de-embedded circuits. Best regards, Yuriy Shlepnev www.simberian.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Moeller, Merrick Sent: Tuesday, November 10, 2009 10:04 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] S-parameter Bisection Is it possible to split a passive S-parameter matrix into two equal sections? For example; given s-parameters for a transmission line of a 10" length can the matrix be split into two 5" lengths. Assume that the passive s-parameter obeys reciprocity. The reason I'm asking is that I have a test fixture on each end of my measurement that I'm trying to de-embed. The insertion loss can be subtracted very easily, but the return loss and other parameters have a great deal of error dealing with de-embedding from one side of the DUT only. I'm hoping to break the fixture into two equal parts without having a direct point of measurement to do so otherwise. Merrick M. Moeller The information contained in this electronic mail message is privileged and confidential information, may be subject to the attorney-client privilege and is intended solely for the use of the addressee. If you are not the intended recipient, any disclosure, copying, distribution, or the taking of any action in reliance on the contents of this message is strictly prohibited. If you have received this message in error, please notify me immediately. ------------------------------------------------------------------ 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 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu