synthesis tools for rat-race design

Is there any tool that synthesizes the design of directional couplers such as (rat-race, quadrature hybrid, ... etc) ? You know, find the width, length, ... of each tx segment.
I already know a bunch of tools which do the work for microstrip and coupled lines but not couplers such as wcalc, appcad, txline awr, ..
My problem is that I need to understand how to design a rat-race coupler (I am working on CST design studio).
Any help will be appreciated