A novel UWB bandpass filter based on multi-stub loaded half-wavelength resonator

In this paper, a novel multi-stub loaded half-wavelength resonator (MSLHWR) is proposed, which exhibits multi-mode resonance and is characterized by three resonant modes of interest. Then, an UWB bandpass filter is designed on it, which can cover the desired UWB bandwidth. Especially, λ/4 open-circuited stubs are introduced at input/output ports, which can create an adjustable transmission zero and then play an important role in improvement of frequency selectivity. Finally, an UWB bandpass filter is fabricated and measured. The measured results show that the filter has good frequency selectivity and as high as 50.7 dB suppression can be achieved at 11.7 GHz. In addition, upper stopband suppression level with at least 25 dB is extended to 16 GHz. The measured group delay variation is less than 0.4 ns in the passband, which is relatively flat.