Compact Triple Notched Bandpass Filter Based on Multimode Resonator

A miniaturized ultra-wideband (UWB) microstrip bandpass filter (BPF) with triple notched Bands using a new multimode resonator (MMR) is designed in this letter. The MMR is accompanied by folded high-impedance interdigital coupled-line structures to achieve a UWB characteristic with triple notched bands. All of the introduced bands are independently controllable to avoid interfering with the other existing operating systems. Besides, with using folded interdigital coupled-line structures, the overall dimensions are significantly reduced, as compared with the UWB BPF using common interdigital coupled-line structures. LC equivalent circuits and the transfer function of the proposed MMR are extracted to analyze the filter. Finally, triple notched bands have been located at 5.4, 8.1, and 10.1 GHz with attenuations of more than -22 dB. The measured results adequately illustrated that the designed filter prepares a passband from 4.2 to 12 GHz plus a wide rejection bandwidth up to 20 GHz.