In the Finite Difference Time Domain (FDTD) method, a discretized form of Maxwellâs equations is solved numerically and simultaneously in both the 3D space and time. During this process, the electric and magnetic fields are computed everywhere in the computational domain and as a function of time starting at t = 0. From knowledge of the primary fields in space and time, one can compute other secondary quantities including frequency domain characteristics like scattering [[parameters]], input impedance, far field radiation patterns, radar cross section, etc.
[[Image:Info_icon.png|40px]] Click here to learn more about the for an overview of '''[[Basic_FDTD_Theory#Differential_Form_of_Maxwell.27s_Equations_.26_the_Yee_Cell | Differential Form of Maxwell's Equations & the Yee CellBasic FDTD Theory]]'''.
Since FDTD is a finite domain numerical technique, the computational domain of the problem must be truncated. At the boundaries of the computational domain, proper boundary conditions must be enforced. In a shielded structure, all objects are enclosed within a perfect electric (or magnetic) conductor box. In an open boundary problem like an antenna, some kind of absorbing boundary conditions such as a perfectly matched layer (PML) must be used to emulate the free space. The absorbing boundaries should act such that the field propagates through them without any back reflection. The FDTD simulation time depends directly on the size of the computational domain and on how close you can place the PML walls to the enclosed objects.