how to assign TEM mode in floquet port in hfss?

in the design, if air box be from -5 to 5, how much de-embed we need? and what happens for S11? its good or not? how it should be?
and in the design you define variable of "a". for what?

Angle of phi what will change? does it change the polarization angles?
Angle of theta what will change?does it change the incident angles?
If number of modes in floquet port be 1 what happens?
For define in the design, TEM mode what i should do?