Ossorio-García, J.; Melgarejo-Lermas, JC.; Boria Esbert, VE.; Guglielmi, M.; Bandler, J. (2018). On the Alignment of Low-Fidelity and High-Fidelity Simulation Spaces for the Design of Microwave Waveguide Filters. IEEE Transactions on Microwave Theory and Techniques. 66(12):5183-5196. https://doi.Abstract-The objective of this paper is to advance the stateof-the-art of Aggressive Space Mapping (ASM) by demonstrating how, for resonant structures, and microwave filters in particular, an ASM based optimization procedure may converge to the desired target performance in just one step. This behavior is first justified in physical terms, using the Electromagnetic (EM) cavity perturbation theory, and is then investigated numerically. Several practical filter design demonstrations are also presented. The paper is concluded with a conceptual definition of Space Alignment in the context of ASM.