Compact ultra-wideband bandpass filter with good selectivity

TLDR: In this paper, a multi-mode resonator (MMR) is proposed to generate four main resonant modes in the desired band, i.e. two odd modes and two even modes.

Abstract: A compact ultra-wideband (UWB) bandpass filter based on a novel multi-mode resonator (MMR) is proposed. The MMR consists of a pair of open-circuited stubs and three pairs of coupled-line sections, which can generate four main resonant modes in the desired band, i.e. two odd modes and two even modes. The measured results of a fabricated one show that its bandwidth can cover the UWB frequency range and it has a sharp skirt due to two transmission zeros near its passband. Return loss in the passband is better than −10 dB. Meanwhile, at least −40 dB suppression can be achieved from 11.86 to 15.13 GHz and −30 dB suppression from 12 to 16 GHz.