Generalized multiport reciprocity analysis of surface-to-surface transitions between multiple printed transmission lines

A method of analysis of surface-to-surface transitions between arbitrary combinations of multilayered printed transmission lines using a general multiport reciprocity formulation is presented. The scattering parameter at a given port of the transition is computed by directly relating it to simple reactions of the known eigenfields of the particular port on various induced strip currents or slot electric fields of other transmission lines. With simplifying practical assumptions, and by use of an efficient singularity extraction technique, equivalent circuit models for particular cases are extracted with simple closed-form expressions for the equivalent circuit parameters. The multiport scattering matrix of the transition completely describes the coupling characteristics of the transition, and via standard network analysis can be conveniently used for design optimization for any port terminations and/or matching circuits. Detailed case studies illustrating the application of the general analysis method are presented