\[Lambda] = 1.; c = 1.;
k0 = (2 \[Pi])/\[Lambda]; \[Omega] = c k0;
\[Alpha] = 4/(k0^2 I); \[Sigma] = (k0^3 Norm[\[Alpha]]^2)/4;
G[r_] := N[I/4 HankelH1[0, k0 Norm[r] ]];
source[{x_, y_}] := E^(I k0 x)*E^(-(y^2/(2*(15)^2)));
Lx = 10; Ly = 20; ndipolesmax = 100;
R = 3*Ly(*6000*);
dipoles = RandomVariate[UniformDistribution[{{-Lx/2, Lx/2}, {-Ly/2, Ly/2}}], {ndipolesmax}];

frames = Table[
   E0 = Table[source[dipoles[[j]]], {j, 1, ndipoles}];
   M = Table[ If[k == j, 1, \[Alpha] k0^2 G[dipoles[[j]] - dipoles[[k]] ] ] , {j, 1, ndipoles}, {k, 1, ndipoles}];
   iM = Inverse[M];
   Escattered = iM . E0;
   Etot[x_, y_] :=(*source[{x, y}]+*) \[Alpha] k0^2 Sum[ G[{x, y} - dipoles[[j]] ] Escattered[[j]], {j, 1, ndipoles}];
   scatteredfield = Table[{\[Theta], Abs[\[Alpha] k0^2 Sum[ G[{R*Cos[\[Theta]], R*Sin[\[Theta]]} - dipoles[[j]] ] Escattered[[j]], {j, 1, ndipoles}]]^2}, {\[Theta], 0, 2 \[Pi], (2 \[Pi])/(5*360)}];
   Show[
    ListPolarPlot[(#[[2]]/Max[scatteredfield[[All, 2]]] + 1.05) & /@ scatteredfield, Joined -> True, Axes -> False, PlotStyle -> Purple],
    DensityPlot[ Abs[Etot[3 Ly x, 3 Ly y]]^2, {x, y} \[Element] Disk[], PlotPoints -> 50, ColorFunction -> "AvocadoColors", PlotRange -> {0, 1}, Frame -> False],
    Graphics[{Orange, PointSize -> 0.005, Point[dipoles[[1 ;; ndipoles]]/(3 Ly)], LightGray, Thick, Circle[], Green, Thick, Arrow[{{-1.4, 0}, {-1, 0}}]}], PlotRange -> {{-2.1, 2.1}, {-2.1, 2.1}}]
   , {ndipoles, 1, ndipolesmax}];
ListAnimate[ Join[Join[Flatten@Table[ Table[frames[[j]], Ceiling[10/(1 + E^(j - 5))]], {j, 1, ndipolesmax}]], Table[frames[[-1]], 10]] ]