Slow-Wave Transmission Line Transformers/Baluns

The design and analysis of a miniaturized transmission line transformer/balun for RF applications is proposed. A novel right-handed slow-wave line using three-dimensional periodic substrate metallization is proposed, where each unit cell is made up of a multilayer loop as a series inductor and parallel strips as a shunt capacitor. DC isolated single-end primary and differential secondary are constructed using three quarter-wave slow-wave lines. A design example is given for a 1:3 voltage ratio at 1.9GHz with slow-wave factors (SWF) between 8~9 for the quarter-wave lines on a three-layer FR4 substrate. The planar dimensions of the electrically small balun are 10mm by 6mm. Details of the designs with simulated and measured data are discussed.