Uniplanar Wideband High-Selectivity Filtering Full-Band-Isolation Baluns Using Novel Out-of-Phase Matching Phase Shifters

Uniplanar wideband high-selectivity filtering full-band-isolation baluns are presented in this article utilizing two different types of out-of-phase matching phase shifters. To obtain high-selectivity performance, half-wavelength open-circuit stubs are introduced. In addition, a single resistor is used for favorable output matching and high full band isolation. By using parallel-coupled n-line technology, the bandwidth of the proposed balun can be controlled. Furthermore, the cascaded coupled-line sections and matching phase shifters are introduced to extend the impedance transforming. For demonstration, two prototypes with center frequency of 3.5 GHz were designed, fabricated, and measured. As expected, measurements show that the proposed baluns have the advantages of bandwidth control, high full-band isolation, impedance transforming, DC-blocking function, stable phase/amplitude imbalances, wideband out-of-band harmonic suppression and high selectivity.