Deterministic extraction of direct source/load coupling and its application to multi-mode filter designs based on transversal array network theory

This is the first report on quantitative evaluation of a direct source/load (S/L) coupling in physical filter models and its application to a synthesis-theory based filter design. The value and sign of the direct S/L coupling can be theoretically synthesized in a circuit model, but they have not been numerically extracted from a physical filter model so far. Using the proposed extraction method makes it possible to predict the direct S/L coupling in physical filter models, thereby enabling filter designs based on a transversal array network theory. As an example, bandpass filters composed of a dual-mode resonator in conjunction with S/L coupling are designed. As a result, both symmetric and asymmetric frequency responses are realized because the maximum number of transmission zeros can be precisely generated at specified finite frequencies with the help of S/L coupling extraction. The usefulness of the proposed method is confirmed through filter designs and measurements.