A Microstrip Bandpass Filter with Ultra Wide Stopband using Folded Stepped-Impedance Resonators

摘要

We developed a bandpass filter using folded stepped-impedance resonators where center frequency is 2 GHz with 60 MHz bandwidth for UMTS (Universal Mobile Telecommunication System) band. Out-of-band rejection is designed by stepped-impedance resonator characteristics, and pass-band is designed by a procedure which is proposed in this paper. The measurement results of a prototype Tchebycheff filter are well agreed with the simulation results on both pass-band and out-of-band ranges. The measured center frequency is 2.01 GHz, pass bandwidth is 69 MHz with 0.3dB-ripple, and pass-band insertion loss is 1.45 dB. The unloaded quality factor Q_o is 488.63. And the out-of-band attenuation is bigger than 30dB from approximately 2.5 to 9.5 GHz.