Compact dual-band bandstop filter using folded resonator

A compact dual-band bandstop filter composed of main transmission line and four folded resonators is presented. Through analyzing the structure of folded resonator, it is found that the main transmission line connected with two proposed folded resonators exhibits the characteristic of band-rejection. Simulated results show that the center frequency of stopband is 2.72 GHz. Then, through adding another pair of folded resonator; a compact dual-band bandstop filter is achieved. Simulated results demonstrate that transmission poles are induced to have better selectivity. Additionally, in order to explain the mechanism of proposed structure, the LC equivalent circuit, analysis of parametric effect and surface current distributions are given. Due to the folded structure, the filter dimensions are reduced and the adjustable stopband is another feature. By virtue of optimization, proposed structure is fabricated. Measured results agree well with the simulation.