DESIGN OF A WIDE-STOPBAND BANDPASS FILTER BY USING DIFFERENT FEEDING POSITIONS OF THE I/O PORTS

In this paper, a wide-stopband bandpass filter is presented. The proposed filter only used two stepped-impedance resonators (SIRs) with a simple electric-coupling structure to accomplish a wide-stopband response. The passband of the proposed filter is designed for global system for mobile communications (GSM) at 1.8 GHz. The Spurious responses of the SIRs are suppressed by controlling the locations of the transmission zeros effectively. The measured results show the passband at 1.8 GHz with a low insertion loss 1.18 dB, and the 3 dB fractional bandwidth (FBW) of 14.1%. The rejection of the stopband is greater than 14 dB from 2.1 to 17.7 GHz, a stopband bandwidth of 9.8 times of the fundamental frequency. The measured result of the fabricated filter also shows a good agreement with the simulated result.