Low‐cost and reliable geometry scaling of compact microstrip couplers with respect to operating frequency, power split ratio, and dielectric substrate parameters

Abstract

A technique for rapid re‐design of miniaturised microstrip couplers with respect to operating conditions as well as material parameters of the dielectric substrate is proposed. The dimension scaling process is based on a set of pre‐optimised reference designs, obtained for an equivalent circuit model of the coupler at hand. The reference designs are utilised to construct an inverse surrogate model which – upon suitable correction – yields the optimum geometry parameter values of the structure re‐designed for required values of operating conditions and substrate parameters. An iterative fine‐tuning process necessary to account for the surrogate model inaccuracies is also developed. The proposed methodology is validated using a compact rat‐race coupler example. The obtained results demonstrate that accurate scaling is possible at a low cost of up to three EM simulations of the structure. For a considered example, the scaling is realised within a wide range of operating conditions (1–2 GHz for the operating frequency, −3 to 0 dB for power split) and substrate parameters (0.7–1.5 mm for the thickness, and 2.5–3.5 for dielectric permittivity). Numerical results are validated experimentally.

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