Compact and sharp rejection microstrip UWB BPF with dual narrow notched bands

This paper presents a new ultra-wideband bandpass (UWB) bandpass filter (BPF) based on the half-wavelength (lambda/2) stepped-impedance stub-loaded resonator (SISLR). Classical even-and odd-mode analysis shows that the new filter has multiple transmission poles and two tunable transmission zeros on both sides of the filter passband. In order to reject the interfered signals, the technique of generating a notched band inside the UWB passband is studied. As examples, two UWB BPFs, one without the notched band and the other with dual narrow notched bands at 5.8/8.0 GHz, are designed, fabricated and measured. The notched band at 5.8 GHz is realized by an embedded open-circuited stub (EOCS) while the notched band at 8.0 GHz is implemented by a folded stepped-impedance resonator (FSIR). The simulations and measurements agree well with each other. Two filters show the simple topologies, compact sizes, low insertion losses and sharp rejections.