A practical method of computer-aided tuning for microwave filters

A practical method for extracting the coupling matrix from measured or electromagnetic simulated S-parameters of narrow band cross-coupled filters with large losses is presented in this paper. The method can be applied to computer-aided tuning or computer-aided design of microwave filters to accelerate the filter design and physical implementation. The modified band-pass to low-pass transformation is applied to remove loss from the simulated or measured S-parameters. The Cauchy method is applied to determine the rational polynomials. A simple practical method is presented to determine the phase shift accurately. After the phase shift effect is removed, it is possible to synthesis a prototype low-pass network using well established techniques once the topology of the filters has been assigned. Two examples verify the method successfully in detail.