A highly selective, tri-band BPF using tri-section SIR with wideband harmonic suppression

This paper presents a compact tri-band bandpass filter, targeting the 2.3–2.5 GHz band for WiFi, the 3.5–3.6 GHz band for 4G mobile communications, and the 4.9–5.1 GHz band for wireless local area networks (WLANs). The proposed filter is based on a tri-section stepped impedance resonator (TSSIR) with arbitrary frequency selection through the control of impedance ratios of the TSSIRs. The filter provides a wide stopband, ranging from 6 to 9.75 GHz with a rejection depth more than 20dB. Wide stopband is achieved by introducing T-shaped feed lines both at the input and output of the filter. The amount of out-of-band rejection is more than four times of that at the fundamental frequency. Measurement results are in good agreement with the 3-D Electromagnetic simulations.