Manipulate[Plot [{Sin[Pi*d/ll*Sin[x]]^2/((Pi*d/ll*Sin[x])^2)},{x,-Pi/10,Pi/10},PlotRange->{0.,1.},AxesLabel->{x,y}],{{d,20,"d"},2,100,Appearance->"Labeled"},
{{ll,2,"lambda"},2,100,Appearance->"Labeled"}]