hi,if u confuse with that method that i already test it with (CST and HFSS) give good comparison
that method has limited to only normal incident,so if u like check any oblique angle,sorry u that method not work well
so i suggest u use floquet mode that allow ur changing the angle of incident ,in CST in frequency solver
in HFSS ,it already supported,i upload artical in HFSS,just look for it here in that site
i check the two method(CST and HFSS) with floquet method,very good result happened
regards