A compact ultra-wideband (UWB) bandpass filter (BPF) with a narrow notched band based on ridged waveguide is presented. Capacitive loading stub structure is introduced to reject the undesired wireless local-area network (WLAN) radio signals. By simply adjusting the height of the capacitive loading post, the centre frequencies of the notched band can be changed from 5.16 to 6.2 GHz, while the bandpass is nearly not affected. The UWB BPF has been simulated, fabricated and measured, with good agreement between the simulated and measured results. The measured insertion loss of the UWB BPF is less than 0.7 dB throughout the pass band of 3.05 to 10.9 GHz, the variation of group delay less than 0.20 ns in this band except for the notched band. The notched band of the BPF centred at 5.2 GHz has 10dB fractional bandwidth of about 3.7%.
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