Accurate extraction of coupling matrix for coupled resonator filters

More accurate and complete formulas are developed for extraction of coupling parameters of coupled resonator filters. It takes into account of coupling with frequency dependence and source/load phase loading. Impacts of resonator port impedance and position are also discussed. Examples, including a wideband comb-line filter and a narrowband dielectric duplexer, are simulated to verify the validity of the presented formulation. Results showed that the extracted coupling matrix (changes with frequency) has the same response with EM simulation. The new formulas enable more accurate and efficient design of coupled resonator filters.