H-Formulation
The full vectorial wave equation for H is given by:
By substituting 
into Equation 1 we get:
The term 
is null.
We can separate Equation 2 into one for longitudinal terms and another one for transversal terms:
for longitudinal terms, and
By substituting
into the first right hand term of Equation 4, we get:
By substituting Equation 5 into the second right hand term of Equation 4, we get:
The third term of Equation 4 can be rewritten as:
By substituting Equation 5 into the second right hand term of Equation 4, we get:
where
