CAD modeling of interdigitated structures

Existing microwave CAD tools, both educational and, with some exceptions, commercial ones, can only model single and symmetric coupled lines. Some tools are also able to analyze multiple-line structures, but they usually adopt a full-wave approach, which is highly computer intensive. Here a modeling strategy for simulating multiple-line TEM structures, using just single and symmetric coupled lines is presented. Some meaningful examples for microwave engineering are included to show how the strategy works. The problem of coupling between nonadjacent lines is also addressed. The aim of this strategy is to provide an effective support for classroom work on interdigitated filters, Lange couplers, and other multiple-line structures.