Complex-Impedance Transforming Marchand Balun

A novel and comprehensive circuit model for designing RF and microwave baluns based on the classic Marchand balun structure are presented and analyzed. Various balun circuits with features of small-circuit size and complex-impedance transformation could be devised based on this new model. As a practical demonstration, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i>-band image-reject (IR) mixer is designed and implemented in 0.25-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m GaN technology, whose RF and local oscillator (LO) baluns are realized by novel complex-impedance Marchand baluns. High-LO-RF port isolation of 40 dB observed from the fabricated mixer is an indication of low amplitude and phase imbalances of the LO and RF balun circuits. Furthermore, the low-conversion loss of 6–8 dB measured for the fabricated mixer, reveals proper complex-impedance transformation of the newly developed Marchand balun.