Wide range suppressed harmonic response compact microstrip balun

In this paper, simple shunt open-stub units are used to design a compact balun with suppressed harmonic response. The stopband response of shunt stubs has been utilized to suppress the harmonic passbands. Design guidelines are presented with equations and graphs based on transmission line model. To validate theoretical predictions, an experimental prototype microstrip balun, with suppressed harmonic passbands up to six times the operating frequency, and occupying only 25% of the conventional balun circuit area is presented.