Analysis and design of impedance-transforming planar Marchandbaluns

A technique for designing impedance-transforming baluns is presented in this paper. It is based on the Marchand balun with two identical coupled lines. By varying the coupling factor of the coupled sections, a wide range of impedance transforming ratios can be achieved. In addition, a resistive network added between the balun outputs is proposed to achieve balun output matching and isolation. Microstrip baluns, matched at all ports, for transforming from a 50-Ω source impedance to 40-Ω as well as 160-Ω load terminations are realized to demonstrate the technique