Investigation of the methods of improving group delay characteristic using complex transmission zeros for coupled resonators filter

Two methods of improving group delay characteristic using complex transmission zeros for coupled resonators filter with attenuation poles in arbitrary stop-band frequencies and with the equal ripple passband attenuation are investigated. Complex transmission zeros of one method contribute to both the attenuation and the phase characteristics, and those of another one contribute only to the phase characteristic. As the results, we show that the quasi equal ripple group delay characteristic is obtained by the former yet an exact one is obtained by the latter.