Abstract
Abstract-If two transmission lines such as microstrip lines are set in the neighborhood, a coupling or crosstalk phenomenon may be generated between them. When the coupling level is low, the phenomenon can be considered as a coupling of external fields by one transmission line to the other transmission line; a set of non-homogeneous differential equations with regard to a line voltage and current holds approximately. The fields can be obtained by estimating vector potentials of currents on the line section and the terminals in terms of a terminal voltage and current of the line concerned. Thus, a solution to the equations can be obtained in expression of a four-port network. Estimation of the coupling between microstrip lines is made by applying the terminal conditions to the expression. To confirm the theory, the experiment has been conducted; the experimental results are in good agreement with the theory.
