Heuristic models of half-wavelength resonator bandpass filter with attenuation poles

Half-wavelength resonator bandpass filters (BPFs) with improved skirt chara cteristics are proposed in a heuristic manner. 'Tapping' for I/O and/or int erstage coupling is the key concept here because the resulting half-wavelen gth open-ended resonators have open stubs which lead to anti-resonances nea r the resonant frequencies. Hence, transmission zeros appear near the reson ant frequencies, i.e. the attenuation poles are created close to the passba nds. Using this concept, excellent bandpass characteristics with multiple a ttenuation poles are obtained by using both I/O and interstage tap-coupling . The results of an experiment involving a coplanar structure are presented which confirm the concept.