Use natural (positive) convention for impedance calculation

Antennas/dipole.pro

@@ -130,8 +130,7 @@ Function {
 
   eta0 = 120*Pi ; // eta0 = Sqrt(mu0/eps0)
 
-  // FIXME: CG "Y[]" should be 0 in 3D !?
-  dR[] = (Flag_3Dmodel) ? Unit[ Vector[Sin[Atan2[Z[],X[]]#1], Y[], -Cos[#1]] ] : Vector[0,0,-1] ;
+  dR[] = (Flag_3Dmodel) ? Unit[ Vector[Sin[Atan2[Z[],X[]]#1], 0, Cos[#1]] ] : Vector[0,0,1] ;
 
 
   V0 = 1. ;