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State of the Art in EM Software for Microwave Engineers White Paper Authors: Jan Van Hese, Agilent Technologies, Inc. Jeannick Sercu, Agilent Technologies, Inc. Davy Pissoort, Agilent Technologies, Inc. Hee-Soo Lee, Agilent Technologies, Inc. Introduction The growing number and complexity of high frequency systems is leading to an increased need for electromag- netic (EM) simulation to accurately model larger portions of the system. There are several different technical approaches to EM simulation, and while no method is generally superior to the others, each one of them is aligned with one or more application areas. This article will discuss the three most established EM simulation technologies: Method-of-moments (MoM), finite element method (FEM) and finite difference time domain (FDTD), linking the simulation technol- ogy to solving specific applications. The method of Overview of the method-of-moments moments Among all techniques to solve EM problems, the method of moments (MoM) is one of the hardest to implement because it involves careful evaluation of Green's functions and EM coupling integrals. Maxwell's equations are transformed into integral equations which upon discretization yield the coupling matrix equation of the structure. The advantage of this transform is that the current distributions on the metal surfaces emerge as the core unknowns. This is in contrast to other techniques which typically have the electric and/or magnetic fields (present everywhere in the solution space) as the core unknowns. Only the surfaces of the metals, where the currents flow, need to be taken into account in the meshing (Figure 1). Hence the number of unknowns (or the size of the matrix) is much smaller. This results in a very efficient simulation technique, able to handle very complex structures. This benefit comes with a price as the integral equations are not applicable for general 3D structures. The key is the availability of the Green's functions. Computation of the Green's functions is only available for free space or for structures that fit in a layered stack up. These so-called 3D planar structures can have any shape in the plane of the layered stack, but can only have vertical geometry features (via's) in the normal direction. Many practical RF or microwave structures fall into this category. Hence the method of moments is a very wide-spread