A novel compact ultra-wideband (UWB) bandpass filter (BPF) with quad-notched bands and wide upper-stopband performance using quad-mode stepped impedance resonator (QMSIR) is proposed in this paper. Firstly, the resonance properties of the proposed QMSIR are studied. The proposed QMSIR is found to have the advantages of introducing quad notched bands and wide upperstopband performance. Then, the proposed QMSIR is employed to achieve four desired notched bands. To validate the design concept, a

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... vel super compact UWB BPF with quad notched bands respectively centered at frequencies of 5.2 GHz, 5.8 GHz, 7.0 GHz, and 8.0 GHz is designed and measured. The predicted results are compared with measured data, and good agreement is reported.