Rapid multi-objective design optimisation of compact microwave couplers by means of physics-based surrogates

The authors introduce a methodology for fast multi-objective design optimisation of miniaturised microwave couplers. The approach exploits the surrogate-based optimisation paradigm with an underlying low-fidelity model constructed from an equivalent circuit of the structure under consideration, corrected through implicit and frequency space mapping. A fast prediction tool obtained this way is subsequently optimised by a multi-objective evolutionary algorithm to identify an initial approximation of the Pareto front, that is, a set of designs representing the best possible trade-offs between conflicting objectives. The correction/optimisation of the surrogate is then iterated by design space confinement and segmentation based on a Pareto set representation obtained thus far in the process. This aims at improving the surrogate model accuracy in the vicinity of the Pareto-optimal solutions. The technique is demonstrated by two design examples of compact rat-race couplers. Experimental validation is also provided.