Design and modeling of twin-spiral coplanar-waveguide-to-slotline transitions

A novel reduced-size twin-spiral coplanar-waveguide-to-slotline transition is proposed in this paper. This twin-spiral transition is based on a modification of quarter-wavelength transformer structure. For design purposes, a hybrid equivalent-circuit model combining transmission-line theory and full-wave simulation is established. Based on this model, various twin-spiral transition structures are carefully examined theoretically and experimentally. Specifically, a twin-spiral transition with 2.26:1 bandwidth and one-quarter the size of conventional ones is achieved. Being simple in fabrication and small in size, the proposed twin-spiral coplanar-waveguide-to-slotline transition is a useful component in uniplanar microwave integrated circuit/monolithic-microwave integrated-circuit applications.