Compact high performance microstrip dual-band bandstop filters for GSM mobile bands

In this paper a compact dual-band bandstop filter (DBBSF) that features two controllable stopbands at desired frequencies is presented. The open stubs of the standard PI network were replaced by Stepped-impedance resonators to realize the dual-stopband characteristics. Here a microstrip circuit is designed at operating frequency for mobile bands (0.9 GHz and 1.9 GHz). The 20 dB fractional band widths at the first and second stop band center frequencies are 9.5 % and 3.5% respectively. The DBBSF simulated by full-wave electromagnetic simulator IE3D to validate the design concept. The main advantage of the proposed design is that it has high rejection level at the two stopbands up to 35 dB; out of band rejection is also 35 dB and symmetrical response about the operating frequency. The full wave simulator IE3D has been used to obtain the physical dimensions of the bandstop filter. Finally, the Full wave Simulated and circuit computed responses of the filter are compared and found to be in good agreement.