UWB bandpass filter with notched band and improved upper stopband characteristics

In this article, we propose a novel ultra-wideband bandpass filter with an improved upper stopband characteristic and a notched band. The proposed BPF is composed of a coupled double-step impedance resonator, an interdigital slot, a dumbbell-shaped defected ground, and an open-loop defected ground. The measured results show a minimum insertion loss of 0.61 dB at 7.02 GHz except about 5 GHz for the WLAN band and a wide upper stopband with more than 30 dB attenuation at up to 20 GHz. The group delay variation in the passband is less than 0.4 ns. In addition, the proposed BPF has a compact size.