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.