ray tracing for lens antenna pattern

hi,
i want hlp in designig antenna with lens,i have designed and simulate antenna now i want to design it with silicon lens but as it will require huge memory so cant be simulated in this way,i saw a paper of d flipovic on double slot antenna wher author used ray tracing method and physical optics for drawing radiation pattern,i am quite new to this sort of designing,can someone plz guide me how to do this and how did they used software for radiation pattern illuminating lens surface plz any one who knows lens simulation plz help me out i am attaching a recent paper i want to adopt the same way but dont know how to do it with software which type of programme is required,plz help me to do this

hi,
if someone answer my following questions it will e easy for me to design lens and antenna.
1.if i have to find current distribution on lens surface then how can i find normal to surface and incident wave?
2.outside lens how can normal factor be found
?
3.any book related to em wave taht deals such topics of ray tracing?