General Formulation for Modeling Bandpass Filters with Finite Quality Factors and Resistive Couplings

Insertion loss can considerably affect the shape of bandpass filters. This effect can be broken down into two different aspects: the finite quality factor of each cavity and the resistive coupling between resonators. This paper presents a general model that can be used to predict the behavior of bandpass filters presenting insertion losses. A technique to extract the required values is also presented for two coupled resonators and the source/load coupling. Finally an inductive post rectangular waveguide bandpass filter is modeled with the proposed technique. The results agree with the full wave simulation obtained from a commercial package.