Ultra-Wideband Bandpass Filter With a Notch-Band Using Stub-Loaded Ring Resonator

A quadruple-mode ultra-wideband (UWB) bandpass filter with a notch-band and wide upper stopband is presented in this letter. The UWB filter is realized using a ring resonator which is loaded with two sets of stubs, i.e., one is loaded in the center and two little stubs at the symmetrical side locations. The loaded stubs are used to create transmission zeros in upper stopband thus high modes are suppressed greatly. Moreover, two identical via-loaded ring resonators are inserted within the stub-loaded ring resonator, to create a notch-band around 5-6 GHz to avoid WLAN signals. Two reflection poles appear in the notch-band, resulting in a switchable bandwidth of the notch-band. Finally, a UWB filter with a notch-band is simulated and fabricated, and measured results provide an experimental validation of predicted performance of the filter.