Fast and precise geometry scaling of miniaturized microstrip couplers with unequal power split

In this paper, a problem of dimension scaling of compact microstrip couplers with unequal power split has been addressed. Using a few reference designs optimized at the level of equivalent circuit model as well as a coupler design optimized for equal power split at the level of its electromagnetic (EM) simulation model, an inverse surrogate is constructed that allows us to precisely re-design the coupler for any required power split ratio at a cost of just one full-wave EM analysis of the structure at hand. Our approach is demonstrated using a miniaturized rat-race coupler operating at 1 GHz.