Bandwidth-enhanced quadrature power splitter and balun using metamaterial transmission lines

In this paper, the bandwidth-enhanced quadrature power splitter (QPS) and balun using metamaterial (MM) transmission lines (TLs) are presented. They consist of a Wilkinson power divider, a conventional TL, and a wellsynthesized MM TL. Since the phase response of the MM TL can be arbitrarily synthesized, the slope of the phase-response curve of the MM TL can be achieved as the same as that of the conventional TL with a specified phase difference, such as 90° or 180°, over a wide frequency range. Two components are designed and implemented at 2 GHz and experimentally demonstrated. The QPS has an output amplitude imbalance of less than 0.9 dB and a phase error of less than ±5° from 1.1-3.5 GHz (104% relative bandwidth), while over the frequency range of 1.24-3.58 GHz (97% relative bandwidth), the balun has an output amplitude imbalance of less than 0.7 dB and a phase error of less than± 10°.