Size reduction of microwave couplers by EM-driven optimization

This work addresses simulation-driven design optimization of compact microwave couplers that explicitly aims at circuit footprint area reduction. The penalty function approach allows us to minimize the area of the circuit while ensuring a proper power division between the output ports and providing a sufficient bandwidth with respect to return loss and isolation around the operating frequency. Computational cost of the optimization process is kept low by exploiting variable-fidelity electromagnetic (EM) simulations, local response surface approximation (RSA) models, as well as suitable response correction techniques. We showcase our approach using an example of a compact rat-race coupler and compare the results to performance-oriented optimization. The reliability of final results is confirmed by experimental data.