Design of the band-pass filter with wide stopband performance using λ/4 forked SIRs

In this paper, a band-pass filter (BPF) using forked stepped-impedance resonators (SIRs) was proposed with having a very wide stopband performance. The circuit composed of two forked SIRs connected with a narrow microstrip with the latter's middle point shorting to the ground through a via hole. The FSIRs filter operated under a quarter-wavelength resonance condition. The filter was built for WLAN IEEE 802.11b/g (2.4/2.45 GHz) applications. A long narrow coupled microstrip which increasing the stopband range was used to couple I/O signal to/from the resonators. The upper stopband, its frequency range was measured from 2.76 to 23.08 GHz with the criterion of the signal rejection levels greater than 20 dB. The stopband's upper-end is over 9.5 f
₀
with the central frequency of 2.44 GHz. Experiment was conducted and a good agreement was observed between the measurement and simulation.