As the frequency increases, more complex wave radiation and propagation effects start to appear and affect the performance of your circuit. At much higher frequencies and in the millimeter wave region of the spectrum, the coupling between adjacent [[Transmission Lines|transmission lines]] may no longer be neglected. In such cases, a full-wave electromagnetic analysis of portions of the circuit might become inevitable. This might be especially true for junction areas and vertical interconnects that join transmission line traces on two sides of a board and across different substrate layers. For accurate analysis of structures of this type you need a full-wave electromagnetic (EM) modeling tool. [[EM.Cube]] is a modular suite of EM simulation tools for this very purpose. Among its computational modules are time domain full-wave simulators like [[EM.Tempo]] based on the Finite Different Time Domain (FDTD) method as well as frequency domain full-wave simulators like [[EM.Picasso]] and [[EM.Libera]] based on different variations of the Method of Moments (MoM).
{{Note | You can analyze a complex passive multiport device in [[EM.Cube]] and import its simulated S-parameter data into [[RF.Spice A/D]] as a new custom devicein your parts database.}}
== Multiport Networks ==