Band-notched Ultra-Wideband Bandpass Filter Using Dual-Mode Resonator Loaded Slotline

In this article, a novel band-notched ultra-wideband (UWB) bandpass filter based on hybrid microstrip/slotline structure is proposed. A quad-mode stubs-loaded slotline resonator is fed by two orthogonal microstrip lines and ultra-wideband bandpass characteristic is excited. A stub-loaded dual mode microstrip resonator is externally loaded to the quad-mode slotline resonator, and a notched band with sharp roll-off characteristic is achieved. The circuit model for the dual-mode microstrip resonator loaded slotline is given and analyzed. The proposed filter is designed and fabricated. Simulated and measured return losses are -12dB/-18dB and -18dB/-10dB in lower and higher passband. The return loss in the notched band is greater than 15 dB.