Miniature 38 GHz couplers and baluns using multilayer GaAs MMIC technology

In this paper, miniature hybrid couplers and baluns using 3D-MMIC technology are presented. These circuits include a branch-line coupler, a rat-race coupler and an "all-ports matched" planar Marchand balun, all designed at the center frequency of 38 GHz. They are fabricated using a multilayer MMIC process employing five metal layers and four layers of BCB dielectric film on a GaAs substrate. With this, size reduction as much as 6 times over their standard counterparts has been achieved and they are thus suitable for the implementations of compact circuits such as balanced mixers and amplifiers.