Crosstalk effects from a cascaded line with different heights to a transmission line

Crosstalk or coupling characteristics between a cascaded line with an abrupt step on the way and a straight transmission line of finite length are discussed comparing measured and calculated results. To analyze the coupling phenomenon, a modified telegrapher\´s equation including the effects of external fields to the lines system is derived. The fields can be obtained by estimating vector potentials of currents in the line and the terminal sections, where the terminals are fabricated like a "via" configuration. A four-port network expression of the voltage and current at each terminal is obtained from solutions of the equation. We have done some experiments to appraise the utility of the theory used here by comparing the transmission characteristics.