A broadband balun using metamaterial phase-shifting lines

A 3-port device that converts a single-ended input to a differential output over a large bandwidth is presented. The balun comprises a Wilkinson divider, followed by a +90° negative-refractive-index (NRI) metamaterial (MM) phase-shifting line along the top branch and a -90° NRI-MM phase-shifting line along the bottom branch. By independently adjusting the parameters of the two MM lines, the slopes of their phase responses can be matched and therefore a broadband differential output signal is achieved. In addition, the MM balun is compact, occupying only a fraction of the area that a conventional TL balun would occupy.