Multi-objective optimization of compact UWB impedance matching transformers using Pareto front exploration and adjoint sensitivities

In this paper, a technique for fast multi-objective optimization of impedance matching transformers has been presented. In our approach, a set of alternative designs that represent the best possible trade-offs between conflicting objectives (here, the maximum reflection level within a frequency band of interest and the circuit size) is identified by directly exploring the Pareto front. More specifically, the subsequent Pareto-optimal design is obtained by local optimization starting from the previously found solution. Low cost of the design optimization process is ensured by exploiting cheap adjoint sensitivities. The proposed technique is demonstrated using an example of three-section transformer matching the 50 Ohm source to the 130 Ohm load and working in 3.1-to-10.6 GHz range. For this example, 16-element representation of the Pareto set is obtained at the cost of just 60 evaluations of the full-wave EM simulation model of the transformer structure.