Miniaturization of microwave hybrid couplers is important for contemporary wireless communication engineering. Using standard computer-aided design methods for development of compact structures is extremely challenging due to a general lack of computationally efficient and accurate simulation models. Poor accuracy of available equivalent circuits results from neglecting parasitic cross-couplings that greatly affect the performance of miniaturized devices. On the other hand, electromagnetic (EM) simulations may be very accurate, but at the same time they are extremely CPU-heavy and time consuming. The methodologies included in this dissertation address the problem of reliable and computationally efficient design of miniaturized hybrid couplers. The proposed methods are based on a generic SBO scheme and employ a number of customized techniques for development of fast and accurate surrogates. These techniques include decomposition, equivalent circuits, EM modeling, response surface approximations, and space mapping. The presented numerical results, confirmed also experimentally, indicate a dramatic reduction in the computational cost of the discussed methods (on average, 25 times speedup in comparison to direct EM optimization). A suite of novel hybrid couplers obtained in this work demonstrate outstanding miniaturization ratios ranging between 82% and 94% with good transmission characteristics. To the best of author’s knowledge, the developed methods are the only procedures so far in the literature that allow for obtaining high-performance EM-validated design solutions of miniaturized hybrid couplers at a low computational cost.