Episode #9:Dielectric Bricks,

Typical situation
Laminate/LTCC/module design houses typically use both 3D planar (MoM) and 3D Full Wave
(FEM) EM solvers. 3D Planar provides very fast and accurate EM simulation results along with
arbitrary passive EM modeling capability (AMC: Advanced Model Composer). Often 3D planar
EM simulation technology is adequate for most laminate/LTCC/module applications, however
there are two cases that require the full wave 3D EM simulations:
1.Applications where the component has to be treated as a dielectric brick. As shown in the above picture,
the top side of the microstrip on the test PCB must be air dielectric to get an accurate port impedance. 
2.Applications where parasitics due to dielectric substrate changes is significant, such as transmission line
structures near the edge of laminates shown as the picture below