Wide Angle (WA), Pade(1,1)

Using the recurrence formula Equation 118, we get:

Here a = 2k₀n_ref .

Using Equation 119 into Equation 131, we get:

Thus,

and,

where

Thus, we can get the unknown field φ ^{l + 1}  at z + Δz from the known field φ ^l  solving the triagonal linear system:

If we consider FEM we get,

Thus, we can rewrite Equation 140 as

here