Accurate Synthesis of Extracted-Pole Filters by Topology Transformations

This letter presents a novel, simpler, and more accurate synthesis method for inline extracted-pole low-pass prototype filters. At the present, this topology is only synthesized by using section extraction or optimization methods, known to suffer from accuracy problems, especially for high-order filters. The method described in this letter relies on the robustness and accuracy of the coupling-matrix synthesis methods by using it as a first step. The second step is instead a transformation to obtain the desired inline extracted-pole topology. Three synthesis examples are presented to validate the novel synthesis procedure.