Modeling and design of multilayer transmission line transformers and baluns

A transmission line balun and a transmission line impedance transformer are described. Both transformers were realized as part of a four-layer laminate PCB using a planar, quasi-coaxial transmission line structure. Approximately a decade bandwidth was achieved, with operating frequencies in the lower and sub Gigahertz range. Both transformers employ the same planar coil geometry, covering an area of less then 0.6 cm². As their power handling capability is merely limited by that of the planar transmission lines, the transformers can be used in medium power applications.