A compact microstrip ultra-wideband (UWB) bandpass filter (BPF) including a narrow notched band within the UWB passband is proposed. The proposed filter is constructed by combination of two highly compact wideband bandpass filters (BPFs) with different physical dimensions which are designed on the basis of a folded-T-shaped stepped impedance resonator (SIR) and parallel-coupling feed structure. The wideband BPFs can be designed separately, and the design procedure is described. The narrow notched band with 3.8% 3 dB fractional bandwidth (FBW) from 5.15 to 5.35 GHz (IEEE 802.11a lower band) is created in order to eliminate interference from wireless local area network (WLAN) with the determined UWB passband. The center frequency and bandwidth of the notched band can be controlled by tuning the structural parameters. The full-wave EM simulated and measured results are in good agreement, showing that the proposed filter possesses good characteristics including wide passband, high selectivity, low insertion loss, large notch deep and sharp rejection.
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