Design of planar, single-layer microwave baluns

This paper describes a microstrip balun as an elementary odd-mode launcher, cascaded with a transversely symmetric network acting as an even-mode stopband filter and an odd-mode impedance transformer. The proposed methodology is illustrated by the design of a rigorously two-dimensional balun with high performance in the range 2.1-3.6 GHz. Such a structure is easy to integrate in microstrip circuits, low cost and free of the parasitics affecting the high frequency operation of other baluns.