Modeling of open-coupled homogeneous striplines

Coupled striplines are used extensively as the basic building blocks for directional couplers and filters in low temperature cofired ceramic. In this paper, we present the modeling of coupled striplines in a homogeneous medium of free space between two parallel ground planes using the finite element method (FEM). FEM is especially suitable and effectivefor the computation of electromagnetic fields in strongly inhomogeneous media. We illustrate that FEM is as suitable and effective as other methods for modeling coupled stripline circuits.We mainly focus on designing of vertical plate broadside-coupled stripline, broadside-coupled stripline, edge-coupled symmetric stripline, asymmetricalcoupled stripline, and asymmetrical broadside-coupled stripline. We compared some of our resultsof computing the capacitance per unit length with those in the literature and found them to be in agreement.