Fast geometry scaling of miniaturized microwave couplers with power split correction

Abstract

Redesigning a microwave circuit for various operating conditions is a practically important yet challenging problem. The purpose of this article is development and presentation of a technique for fast geometry scaling of miniaturized microwave couplers with respect to operating frequency. Our approach exploits an inverse surrogate model constructed using several reference designs that are optimized for a set of operating frequencies within a range of interest. For the sake of computational efficiency, the reference designs are obtained for an equivalent network model of the coupler. The surrogate directly predicts the optimum values of geometry parameters of the structure at hand corresponding to a requested operating frequency. By introducing appropriate correction, the model allows for coupler scaling at the EM simulation model level. Because the surrogate does not carry information about the power split ratio of the coupler, an additional analytical corrective procedure is developed to ensure an equal power split of scaled structure. The computational cost of the scaling procedure corresponds to only two EM analyses of the circuit at hand (including both correction steps). The operation and performance of our technique is demonstrated using a compact microstrip rat-race coupler scaled for the operating frequency range of 0.5-2.5 GHz. Experimental validation is also provided.