Precise design of multilayer circuit using finite differences techniques

The design of multilayer directional couplers with septum is often done using the spectral domain technique. This technique consists in taking the Fourier transform of the boundary conditions and then expressing the charge distribution on the conductor, ρ
i
and the septum, ρ
s
as a function of G
ij
, the Green function . Galerkin optimization technique is then used to compute ρ
i
and ρ
s
as a summation of arbitrary chosen basis functions, e.g., equation A proper choice of basis functions determines the precision and convergence of results.