AbstractAs monolithic integration of the microwave circuits progresses, the microstrip line used as a fundamental transmission medium becomes extremely small in size. As the transmission line is miniaturized, it becomes necessary to consider the effect of the shape of the edges of the strip conductor in addition to the thickness. In this paper, an integral equation is derived for the charge density distribution on the strip conductor surface as the unknown. The transmission line characteristics are obtained by discretizing the integration range. Further, the effect of the trapezoidal cross section of the strip conductor formed by etching and plating on the characteristic parameters is specifically studied.