The arrival of electromagnetic (EM) simulation tools has not eclipsed the relevance of CAD models for microwave and millimeter-wave integrated circuits. In this article, an overview of the existing CAD models for suspended and inverted microstrips is presented. Comparisons of the various CAD models with rigorously obtained theoretical data are presented, followed by comparisons against available experimental data. Areas needing further research are also identified. (C) 2004 Wiley Periodicals, Inc.