Multiport SOLR calibrations: performance and an analysis of some standards dependencies

Short-Open-Load-Reciprocal (SOLR) has been used as a calibration technique when the realization of a good thru line is difficult. This may happen in on-wafer environments (e.g., when probes are orthogonal or when two-signal probes are used), in coaxial measurements (when different connector types are involved), or in fixtured measurements. The increasing number of multiport S-parameter measurements has further pushed demand for such an algorithm as probe and connector configurations proliferate. Several issues related to a practical implementation of multiport SOLR measurements are covered in this paper including thoughts on optimal combinations of thrus and reciprocal networks when choice is available, some limits on the behavior of reciprocal networks and how they affect standards choices, and a heuristic analysis of the use of redundant thrus/reciprocals in the multiport environment. Load match benefits the most from true thrus, when available, but transmission tracking seems less sensitive for a wide variety of networks. Thus, a careful selection of standards employed can, in some sense, optimize the multiport calibration in this environment.