Compact, low insertion loss, sharp rejection wideband bandpass filters using dual-mode ring resonators with tuning stubs

Novel wideband bandpass filters using dual-mode ring resonators with orthogonal direct-connected feed lines and tuning stubs are developed. The tuning stubs act as series resonators and provide sharp rejections for the filters. Also, a perturbation stub in each ring influences the fields of the ring resonators and generates a dual mode to extend the stop bands of the filters. The simulated and measured results agree well. This novel bandpass filter has advantages of compact size, low insertion loss, and sharp rejection