Changes

where <math> R=|r-r'| \text{, } k_0 = \frac{2\pi}{\lambda_0} \text{ and } Z_0 = 1/Y_0 = \eta_0 </math>., '''R''' ='''r''' - '''r'''', R = |'''R'''|, and :<math>\mathbf{ \hat{R} = \frac{R}{|R|} = \frac{r-r'}{|r-r'|} }</math>