UWB Filtering Balanced Power Divider With Wide Upper Stopband and Tunable Notch Band

This letter presents a tunable notch band ultra-wideband (UWB) filtering balanced power divider (FBPD) using a hybrid microstrip/slot-line structure for effective common-mode (CM) suppression and differential-mode (DM) transmission. The innovative design enhances upper stopband suppression by incorporating a pair of open-circuit stubs on each side of the microstrip structure. Additionally, a short-circuit stub loaded with a varactor diode enables tunable notch band functionality. This configuration achieves a wide upper stopband and a tunable notch band with excellent frequency selectivity, enhancing versatility over conventional designs. Finally, the proposed UWB FBPD was fabricated and measured. The measurement results show a 120% DM 3dB fractional bandwidth (FBW). The CM suppression exceeds 28.7dB over the 2–8GHz passband, and the DM upper stopband suppression exceeds 20.7dB up to 20GHz (4f0). The DM isolation exceeds 14.1dB within the passband, and the notch frequency (NF) is tunable from 4.5 to 5.4GHz.