Whenever solving for more than a single vector component, it is not possible to use Lagrange elements for electromagnetic wave modeling. The reason is that they force the fields to be continuous everywhere. This implies that the physics interface conditions, which specify that the normal components of the electric and magnetic fields are discontinuous across interior boundaries between media with different permittivity and permeability, cannot be fulfilled. To overcome this problem, the Electromagnetic Waves, Frequency Domain interface uses vector elements, which do not have this limitation.

The solution obtained when using vector elements also better fulfills the divergence conditions ∇ · D = 0 and ∇ · B = 0 than when using Lagrange elements.