Design of a bandpass filter with multiple attenuation poles based on tapped resonators

An intrinsic property of a tapped resonator is elucidated here, and a novel bandpass filter (BPF) with improved skirt characteristics based on a tappe d half-wavelength resonator is proposed by this intrinsic property. "Tappin g" for both I/O and interstage couplings of the resonator is the key concep t here because a resulting open-ended resonator makes shunt open stubs whic h give anti-resonance near the center frequency. Multiple attenuation poles appear near the center frequency namely, close to, the passband. A BPF is designed on the basis of the general filter theory with a narrow band appro ximation. An experiment is carried out to confirm the concept by using a co planar structure. The expected bandpass characteristics with multiple atten uation poles have been obtained by the novel BPF designed by the present co ncept.