Expedited Geometry Scaling of Compact Microwave Passives by Means of Inverse Surrogate Modeling

In this paper, the problem of geometry scaling of compact microwave structures is investigated. As opposed to conventional structures [i.e., constructed using uniform transmission lines (TLs)], re-design of miniaturized circuits (e.g., implemented with artificial TLs) for different operating frequencies is far from being straightforward due to considerable cross-couplings between the circuit components. Here, we develop a simple and computationally efficient methodology for dimension scaling of the compact circuits. The proposed approach utilizes an equivalent circuit representation to identify a fast inverse model that determines the relationship between the geometry parameters of the structure at hand and its operating frequency. Upon suitable correction, the inverse model is applied to find dimensions of the scaled design at the high-fidelity (electromagnetic (EM) simulation) model level. Owing to reasonable correlations between the low- and high-fidelity models, the circuit geometry scaled to a requested operating frequency can be found using just a single EM simulation of the structure, despite possible absolute discrepancies between the models. The proposed methodology is demonstrated using two exemplary compact couplers scaled in wide ranges from 0.5 to 2 GHz and from 0.5 to 1.8 GHz, respectively. The numerical results are supported by physical measurements of the fabricated coupler prototypes.