You should google for "gnuplot antenna z axis", see what they are doing, and adapt it to your problem. The Perl part is the easiest, and you have 2 choices.... write your gnuplot script in the gnuplot script style and feed it to the c gnuplot program via IPC in the Perl script; OR use Term::Gnuplot

The hard part is figuring out your formulas, and putting into a gnuplot script. A good start is at gnuplot-3d

You would be better off asking this on a gnuplot maillist ( of course your teacher will see your posts. as well as this one, so if you want a good grade, do it yourself). :-)