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.