Chapter 12: Applications of Multi-Objective Optimization

The goal of multi-objective optimization — as understood in this book — is to find comprehensive information about a given structure in the form of a set of alternative designs representing the best possible trade-offs between conflicting objectives. The numerical methods presented in Chapters 7 and 8, and demonstrated in Chapters 9 and 11, allow for finding such Pareto sets in reasonable timeframes, even for relatively expensive high-fidelity electromagnetic (EM)-simulation models. In this chapter, we demonstrate utilization of Pareto sets for comprehensive comparison of various antenna structures and microwave circuits. Three case studies are considered. The first one involves three structures of compact ultra-wideband (UWB) antennas, where information about available size-performance trade-offs allow for conclusive comparison of the competing antenna topologies. The second case is a comparison of two structures of UWB monopole antennas that are topologically similar, yet a small modification leads to considerable performance improvement in terms of attainable miniaturization rate. The last study investigates selection of the best possible architecture for compact impedance matching transformers, specifically, the optimum type and arrangement of the compact cells utilized as the basic building blocks of the transformer structure. In all cases, the knowledge of Pareto fronts is indispensable to make application-driven design decisions. At the same time, it is pointed out that the antenna dimensions reported in the literature are often far from the optimum ones; consequently, various comparisons of antenna structures provided in the published works might be of limited use.