On the Relation Between Stored Energy and Fabrication Tolerances in Microwave Filters

In this paper, a new approach for the sensitivity analysis of microwave filter networks is presented. It is shown that the standard method of sensitivity calculation based on a tuned filter is only valid for infinitesimal geometry changes and not meaningful for practical tolerance values. However, when the sensitivity calculation is expanded to also include sensitivities of detuned filters, it is shown that accurate tolerance predictions can be made even for large geometry variations. It is found that sensitivities can be related to the stored energy distribution in the filter. Transversal and ladder network-type topologies are examined, and it is demonstrated for the first time that, for in-line topologies, sensitivity can be predicted directly from the group delay of the filter in Chebyshev filters. In order to demonstrate the usefulness of the results obtained, the maximum degradation of the in-band performance has been directly obtained from the group delay for different inline filters.