Surrogate modeling for expedited two-objective geometry scaling of miniaturized microwave passives

Geometry scaling of compact microwave structures is a challenging problem because of complex relationships between the physical dimensions of the circuit and its electrical characteristics, which is mostly caused by considerable cross-couplings in densely arranged layouts. Yet, possibility of rapid redesign of a structure for various sets of design specification is important from practical point of view. In this article, we develop a procedure for expedited dimension scaling of compact microwave couplers with respect to two independent criteria. Our approach exploits inverse surrogates constructed at the level of equivalent circuit model and correction techniques that permits low-cost re-design of the coupler structure (at the level of EM-simulation model) for a required operating frequency and power split ratio. The procedure is demonstrated using a folded microstrip rat-race coupler. The scaling range for the considered example is from 0.5 to 2.0 GHz for the operating frequency, and from −6 dB to 0 dB for the power split ratio.