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

Half-wavelength resonator bandpass filters (BPFs) with improved skirt characteristics are proposed in a heuristic manner. `Tapping´ for I/O and/or interstage coupling is the key concept here because the resulting half-wavelength open-ended resonators have open stubs which lead to anti-resonances near the resonant frequencies. Hence, transmission zeros appear near the resonant frequencies. i.e. the attenuation poles are created close to the passbands. Using this concept, excellent bandpass characteristics with multiple attenuation 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