Asymmetric dual-line coupling structure for multiple-notch implementation in UWB bandpass filters

A novel asymmetric dual-line coupling structure is presented for multiple-notched-band implementation in an ultra-wideband (UWB) bandpass filter (BPF). This structure has been applied to a single-stage UWB BPF to produce multiple narrow notched bands inside its passband. Based on the asymmetric dual-line coupling structure, an UWB BPF with multi-notched bands has been designed, fabricated, and measured. Measured results agree closely with simulated ones. The two notched bands of the BPF centred at 4.9 and 8.55 GHz have 10 dB fractional bandwidths of about 2% and 5.8%, respectively.