Compact wideband bandpass filter using fish spear‐shaped multimode resonator

Abstract

ABSTRACTA compact wide‐band pass filter (BPF) with sharp band rejection characteristics and wide upper stopband is presented in this article. The proposed bandpass filter is designed using a fish spear‐shaped multimode resonator (MMR). This fish spear‐shaped MMR has four arms and have five resonant modes, out of which three are even modes and the remaining two modes are odd. These modes lie in the wide frequency spectrum and they are used to realize the wideband passband of the filter. These five modes are brought closer by optimizing the dimensions of fish spear‐shaped MMR to get the desired passband. To improve out‐of band performance, a stepped impedance resonator is added at the central plane. The proposed wideband BPF filter have fractional bandwidth better than 85%. Moreover, to verify the proposed concept the designed filter is fabricated and measured. The measured bandwidth of proposed filter is 6.82 GHz and is from 2.55 to 9.37 GHz with an insertion loss of 2 dB. The measured return loss of the filter is better than 10 dB in the entire designed wideband. Measured results are validated with the simulated results. The group delay variation is less than 0.25 ns. A wide stopband with 15 dB attenuation is extended up to 20 GHz is obtained. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2833–2837, 2015