Miniaturized branch‐line hybrid circuit using 3D MMIC quasi‐distributed TFMS lines

Abstract

SUMMARYThis paper discusses a miniaturized branch-line hybrid circuit consisting of quasi-distributed TFMS lines, making use of the topological characteristics of the threedimensional MMIC. In the three-dimensional MMIC, it is possible to reduce the coupling between adjacent transmission lines due to their very fine structure. Hence, miniaturized meander-like lines can easily be realized. Further, due to the stacking effect in this technique, MIM (metal-insulator-metal) capacitors can easily be installed into the transmission line. In this paper, by utilizing these effects, a transmission line consisting of high-impedance TFMS lines and MIM capacitors is proposed. The TFMS line of this type is here called a QD-TFMS (Quasi-Distributed Thin Film MicroStrip) line. First, the characteristics of the QD-TFMS line are obtained by simulation and the size reduction effect is verified. Further, miniaturization of the branch-line hybrid circuit using the QD-TFMS lines is discussed. It is demonstrated that the fabricated circuit can be miniaturized to an area ratio of less than 20% in comparison with a branch-line hybrid circuit using only meander-like lines.