Design of narrowband microwave filters with mixed-topology

Narrow band microwave filters exhibiting transmission zeros in the response (either imaginary and/or complex) can be typically designed with cross-coupled or extracted pole topologies. These configurations present pro & cons which must be carefully considered during the choice of a specific topology. In some cases it could be however very convenient the choice of a mixed topology, i.e. part of the structure with extracted-pole and part with cross-coupled configuration. Unfortunately, even if several well established techniques are available in the literature for the cross-coupled or extracted-pole synthesis taken separately, nothing can be found for the design of mixed-topology filters (apart direct optimization)