Design of UWB Bandpass Filter with Dual Notched bands

A compact microstrip ultra-wideband (UWB) bandpass filter (BPF) with two narrow notched bands in the passband is presented in this letter. Firstly, a multi-mode resonator (MMR) with an embedded open-circuited stub is utilized in the filter design. Such an MMR structure leads to bring out a notched band. The length of the stub can be tuned to select a specific frequency for one of the notched bands. Secondly, Asymmetric parallel-coupled lines are applied to the input and output (I/O) to produce another notched band in the passband, and furthermore the location of the notched band can be adjusted by changing the length of the stubs loaded on the coupled lines. Finally, a prototype filter is designed and fabricated, and its measured results are provided to verify the predicted frequency response.