Thanks. Managed to get the structured paraboloid using gmsh.

c = 299792458;
f = 3.0e9;
lambda = c/f;
D = 1.25*lambda;
f2d = 0.72;
focallength = D*f2d;
parabolLowerEdgeHeight = -D/2;
parabolPoints = 11;
delta = D/(parabolPoints-1);
h = lambda/12;
For i In {0:parabolPoints-1}
x = (i*delta)+parabolLowerEdgeHeight;
z = (x*x)/(4.0*focallength);
points1[i] = newp;
Point(points1[i]) = {x, 0, z, h};
EndFor
x = ((parabolPoints-1)*delta)+parabolLowerEdgeHeight;
z = (x*x)/(4.0*focallength);
Point(12) = {0, 0, z};
Spline(1) = points1[];
Split Line(1) {6};
Rotate {{0, 0, 1}, {0, 0, 0}, Pi/2} { Duplicata { Line{2}; } }
Rotate {{0, 0, 1}, {0, 0, 0}, Pi/2} { Duplicata { Line{3}; } }
Circle(6) = {11, 12, 23};
Circle(7) = {23, 12, 1};
Circle(8) = {1, 12, 13};
Circle(9) = {13, 12, 11};
Line Loop(10) = {3, 6, -5};
Line Loop(12) = {5, 7, 2};
Line Loop(14) = {2, -4, -8};
Line Loop(16) = {4, 3, -9};
Surface(11) = { -10};
Surface(13) = { -12};
Surface(15) = { 14};
Surface(17) = { 16};
Physical Surface("reflector") = {15, 17, 11, 13};
//+
Transfinite Surface {11};
//+
Transfinite Surface {13};
//+
Transfinite Surface {17} Right;
//+
Transfinite Surface {15} Right;
//+
Recombine Surface {13, 11, 17, 15};