[[Image:FDTD133.png|thumb|200px|Far Field Background Medium dialog.]]
===Radiation Pattern Above A a Half-Space Medium===
As mentioned earlier when discussing boundary conditions and computational domain, you can use CPML boundary conditions with zero offsets to model a structure with infinite lateral extents. At the end of the FDTD simulation, the far fields are calculated using the near-field-to-far-field transformation. This calculation requires the dyadic Green's function of the background structure. By default, the FDTD engine uses the free space dyadic Green's function for the far field calculation. In general, the [[FDTD Module]] features dyadic Green's functions for four scenarios:
Note that the current version of [[EM.Cube]]'s [[FDTD Module]] does not calculate the far-field Green's function of a laterally infinite, conductor-backed, dielectric substrate with a finite layer thickness. For problems of this type, you should use [[EM.Cube]]'s [[Planar Module]]. In FDTD, either your PEC/PMC ground can be infinite or you can assume a dielectric half-space ground. Also, note that when infinite lateral dimensions are not required, like in the case of patch antennas with a finite substrate and finite ground, FDTD is the method of choice, as the planar MoM method cannot handle such cases.
{{twoimg|<table><tr><td> [[Image:fdtd_out36_tn.png|thumb|360px|Radiation pattern of a vertical short dipole above PEC ground|.]] </td><td> [[Image:fdtd_out37_tn.png|thumb|400px|Radiation pattern of a vertical short dipole above PMC ground}}.]] </td></tr>{{twoimg|</table><table><tr><td> [[Image:fdtd_out38_tn.png|A thumb|200px|Radiation pattern of a horizontal short dipole above a PEC ground|.]] </td><td> [[Image:fdtd_out39_tn.png|thumb|200px|Radiation pattern of a horizontal short dipole above a PMC PEC ground. The bottom (-Z) boundary is set to PEC or PMC, even though it is not visible.}}]] </td></tr></table>
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