Iss= { 
0.0018,
0.0002,
0.0022,
0.0008,
0.0154,
0.0251,
0.0355,
0.0448,
0.0524,
0.0564,
0.0576,
0.0552,
0.0477,
0.0390,
0.0319,
0.0215,
0.0124,
0.0056,
0.0002,
0.0023,
0.0079,
0.0157,
0.0253,
0.0344,
0.0438,
0.0519,
0.0570,
0.0576,
0.0559,
0.0511,
0.0430,
0.0442,
0.0333,
0.0229,
0.0126,
0.0059,
0.0013
};
I0 = 0.786;
Phis = Table[x, {x,0,2*Pi ,Pi/18}];
NIss = Function[x, x/Max[Iss]]/@ Iss;
Args = Table[ {Phis[[i]], NIss[[i]]}, {i, 1,36}];

Graph1 = ListPolarPlot[Args,Joined->True,PolarAxes->Automatic,PolarGridLines->{Automatic,None},PolarAxesOrigin->{0,1}, PolarTicks->{"Degrees", Automatic}];
Graph2 = PolarPlot[(Cos[x- 10Pi/18])^2,{x,0,2Pi}, PolarAxes->Automatic,PolarGridLines->{Automatic,None}, PolarAxesOrigin->{0,1},PolarTicks->{"Degrees", Automatic}, PlotStyle->Red];
Kp = Max[Iss]/I0
Kpr = Min[Iss]/I0
Show[Graph1,Graph2]