Frequency Correction Design Technique for Additive Manufactured Cavity Filters

In this work, a refinement of the classical coupled-cavity filter design technique is presented. This refinement consists of a central frequency correction when calculating inter-resonator cavity couplings. The correction introduced is specially critical when 3D shapings are applied to empty cavities, since both resonators and couplings become more dispersive, and frequency tuning is harder due to an increased sensitivity with the resonator geometry. To validate the design approach, a filter design with shaped cavities is realised, where it can be seen that the traditional design technique leads to a starting point which is significantly far from the target specifications. However, the use of the new technique increases the accuracy of its initial response, allowing a simpler final optimization process. The technique presented can have big impact in the efficient design of future filter structures, where 3D shapings are applied to improve performances.