Here are a number of microwave calculators that have been used, both at microwave and RF. The stripline calculators some of those.
Simple calculator for the characteristic parameters of a perfect microstrip ie; stripline, in various formats... Add a real substrate from the catalog.
A calculator for a perfect microstrip coupler (stripline).There next to no dispersion here, if the right substrate is used. Add a real substrate from the catalog.
Try to put any power into a close coupled edge coupler an I guarantee it will chisp over. A much better choice is a broadside coupler with or without an interplate dielectric. Higher odd mode coupling makes the life of a 3db hybrid power combiner much easier
A calculator orientated towards high power use of stripline/slabline for example 3db couplers for combining Band 11 transmitters up to 50Kw.