===Radar Cross Section===
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[[Image:FDTD131.png|thumb|300px|[[FDTD Module]]'s RCS dialog]]
When the physical structure is illuminated by a plane wave source, the calculated far field data indeed represent the scattered fields. In that case, the incident and scattered fields can be separated. EM.Cube can calculate the radar cross section (RCS) of a target defined as:
* At the end of an FDTD simulation, besides calculating the RCS data over the entire (spherical) 3D space, a number of 2D RCS graphs are also generated. These are indeed RCS cuts at certain planes, which include the three principal XY, YZ and ZX planes plus one additional constant f-cut. This latter cut is at f = 45° by default. You can assign another f angle in degrees in the box labeled '''Non-Principal Phi Plane'''.
[[ImageAt the end of an FDTD simulation, in the far field section of the Navigation Tree, you will have the θ and φ components of RCS as well as the total radar cross section:FDTD131σ<sub>θ</sub>, σ<sub>φ</sub>, and σ<sub>tot</sub>.png]]Â Figure 1: [[FDTD Module]]You can view a 3D visualization of these quantities by clicking on their entries in the Navigation Tree. The RCS values (σ) are expressed in m<sup>2</sup>. The 3D plots are normalized to the maximum RCS value, which is displayed in the legend box. The 2D RCS graphs can be plotted in 's ''EM.Grid '''exactly in the same way that you plot 2D radiation pattern graphs. A total of eight 2D RCS dialoggraphs are available: 4 polar and 4 Cartesian graphs for the XY, YZ, ZX and user defined plane cuts. at the end of a sweep simulation, EM.Cube calculates some other quantities including the backscatter RCS (BRCS), forward-scatter RCS (FRCS) and the maximum RCS (MRCS) as functions of the sweep variable (frequency, angle, or any user defined variable). In this case, the RCS needs to be computed at a fixed pair of φ and θ angles. These angles are specified in degrees as '''User Defined Azimuth & Elevation''' in the "Output Settings" section of the '''Radar Cross Section Dialog'''. The default values of the user defined azimuth and elevation are both zero corresponding to the zenith.
At the end of an FDTD simulation, in the far field section of the Navigation Tree, you will have the θ and φ components of RCS as well as the total radar cross section: σ<sub>θ</sub>, σ<sub>φ</sub>, and σ<sub>tot</sub>. You can view a 3D visualization of these quantities by clicking on their entries in the Navigation Tree. The RCS values (σ) are expressed in m<sup>2</sup>. The 3D plots are normalized to the maximum RCS value, which is displayed in the legend box. The 2D RCS graphs can be plotted in '''EM.Grid '''exactly in the same way that you plot 2D radiation pattern graphs. A total of eight 2D RCS graphs are available: 4 polar and 4 Cartesian graphs for the XY, YZ, ZX and user defined plane cuts. at the end of a sweep simulation, EM.Cube calculates some other quantities including the backscatter RCS (BRCS), forward-scatter RCS (FRCS) and the maximum RCS (MRCS) as functions of the sweep variable (frequency, angle, or any user defined variable). In this case, the RCS needs to be computed at a fixed pair of φ and θ angles. These angles are specified in degrees as '''User Defined Azimuth & Elevation''' in the "Output Settings" section of the '''Radar Cross Section Dialog'''. The default values of the user defined azimuth and elevation are both zero corresponding to the zenith. <font color="red"><u>'''{{Note that unlike |Unlike EM.Cube's Planar, MoM3D and Physical Optics Modules, the [[FDTD Module]] currently does not support 3D mono-static RCS calculation due to the enormous amount of computational work needed. Only the bi-static RCS is calculated for a given plane wave source. '''</u></font>}}
[[Image:FDTD132.png|800px]]