A compact narrow-band bandstop filter using spiral-shaped defected microstrip structure

A novel compact narrow-band bandstop filter is implemented by using the proposed spiral-shaped defected microstrip structure (SDMS) in this paper. Compared with other DMSs, the presented SDMS exhibits the advantage of compact size and narrow stopband. Meanwhile, an approximate design rule of the SDMS is achieved and the effects of the dimensions on the resonant frequency and 3dB fractional bandwidth (FBW) are analyzed in detail. Both the simulation and measurement results of the fabricated bandstop filter show that it has a 10 dB stopband from 3.4 GHz to 3.6 GHz with more than 45 dB rejection at the center frequency.