Diagnosis and tuning of multiple coupled resonator filters

A robust and efficient tool for extraction of coupling matrix in multiple coupled resonator filters (MCRF) is presented. After collecting frequency samples of the filtering function either from electromagnetic simulations or from measurements, a model based parameter extraction (MBPE) technique is employed to approximate these samples by a rational function using Cauchy method. For lossy filters, the effect of loss is removed from the approximated filtering function by properly shifting its zeros and poles. Finally, lossless models for scattering parameters are obtained in terms of rational functions from which the coupling matrix is extracted through a synthesis and optimization process. The method is employed for diagnosis and tuning of three practical bandpass filters.