TCanvas c("myCanvas","myCanvas",600,600);
Double_t rmin=0.;
Double_t rmax=TMath::Pi()*6.;
const Int_t npoints=1000;
Double_t r[npoints];
Double_t theta[npoints];
for (Int_t ipt = 0; ipt < npoints; ipt++) {
    r[ipt] = ipt*(rmax-rmin)/npoints+rmin;
    theta[ipt] = TMath::Sin(r[ipt]);
}

TGraphPolar grP1 (npoints,r,theta);
grP1.SetTitle("A Fan");
grP1.SetLineWidth(3);
grP1.SetLineColor(2);

grP1.Draw("L");
c.Draw();