Use of a finite difference time‐domain method to analyze thin‐film microstrip lines with conductor loss

Thin-film microstrip lines have been proposed in which microwave transmission lines and circuit elements are placed between or on the metal and insulating layered films on a GaAs substrate. These configurations are intended for size reduction of microwave circuits, realization of new circuit topologies, and improvement of design capability. On the other hand, the finite difference time-domain method has attracted attention as one of the general-purpose analysis methods for three-dimensional configurations. It has been demonstrated that this method is capable of analyzing substantially complex geometry. However, in the conventional finite difference time-domain method, the conductors usually are treated as perfect and infinitely thin metals. Hence, the conventional method cannot be applied to the thin-film microstrip lines in which the conductor thickness cannot be neglected in comparison with the transmission line dimensions. In the present study, the conductor thickness is taken into consideration and the formulation is carried out including the conductor loss. In the conductor, the discretization spacing is made sufficiently smaller than the conductor thickness while the discretization step is made larger where the field variation is gradual. In this way, the main storage capacity needed is reduced and the computation time is shortened. Thin-film microstrip lines of several shapes are analyzed and the frequency characteristics of the transmission line parameters, the electromagnetic field distributions and the Poynting power distribution are derived. Thus, the validity of the method and its range of applications are shown.