microstrip transition
You can handle the edge mount SMA like any other transition, that involves a change of the conductor width, e.g. between a coaxial connector and a cable. By moving the position of the width step you can almost zero the discontinuity. The effect can be visualized best with a TDR measurement. But for a few GHz range, thé transition isn't that critical, as already mentioned by Azulykit. A single step betweeen the SMA center conductor and the microstrip should be sufficient. If targetting to the high GHz range, you should consider that microstrip is an open transmission line, that produces some dispersion (in the form of radiation losses) anyway.