Radiation pattern of a 4-element dipole array: (Left) computed using array factor and (Right) computed by simulating an array object.
=== Computing Radar Cross Section ===
[[File:wire_pic49.png|thumb|300px|[[MoM3D Module]]'s RCS dialog]]
When the wire-frame your structure is excited by a plane wave source, the calculated far field data indeed represent the scattered fields. [[EM.Cube|EM.CUBE]] calculates Libera can calculate the radar cross section (RCS) of a target, which is defined in the following manner: :<math> \sigma = 4\pi R^2 \cdot \frac{|E_{scat}|^2}{|E_{inc}|^2} </math><!--[[File:rcs_equation.png]]--> [[EM.Cube|EM.CUBE]] calculates three Three RCS quantitiesare computed: the φ and θ components of the radar cross section as well as the total radar cross section: σ<sub>θ</sub>, σ<sub>φ</sub>, and σ<sub>tot</sub>. In addition, [[EM.Cube|EM.CUBE]] [[MoM3D Module]] Libera calculates two types of RCS for each structure: '''Bi-Static RCS''' and '''Mono-Static RCS'''. In bi-static RCS, the structure is illuminated by a plane wave at incidence angles θ<sub>0</sub> and φ<sub>0</sub> and the RCS is measured and plotted at all θ and φ angles. In mono-static RCS, the structure is illuminated by a plane wave at incidence angles θ<sub>0</sub> and φ<sub>0</sub> and the RCS is measured and plotted at the echo angles 180°-θ<sub>0</sub> and φ<sub>0</sub>.It is clear that in the case of mono-static RCS, the Wire MoM simulation engine runs an internal angular sweep, whereby the values of the plane wave incidence angles θ<sub>0</sub> and φ<sub>0</sub> are varied over the intervals [0°, 180°] and [0°, 360°], respectively, and the backscatter RCS is recorded.
To calculate RCS, first you have to define an RCS observable instead of a radiation pattern. Right click on the '''Far Fields''' item in the '''Observables''' section of the Navigation Tree and select '''Insert New RCS...''' to open the Radar Cross Section Dialog. Use the '''Label''' box to change the name of the far field or change the color of the far field box using the '''Color''' button. Select the type of RCS from the two radio buttons labeled '''Bi-Static RCS''' and '''Mono-Static RCS'''. The former is the default choice. The resolution of RCS calculation is specified by '''Angle Increment''' expressed in degrees. By default, the θ and φ angles are incremented by 5 degrees. At the end of a Wire MoM simulation, besides calculating the RCS data over the entire (spherical) 3-D space, a number of 2-D RCS graphs are also generated. These are RCS cuts at certain planes, which include the three principal XY, YZ and ZX planes plus one additional constant φ-cut. This latter cut is at φ=45° by default. You can assign another phi angle in degrees in the box labeled '''Non-Principal Phi Plane'''.
At the end of a Wire MoM simulation, the thee RCS plots σ<sub>θ</sub>, σ<sub>φ</sub>, and σ<sub>tot</sub>are added under the far field section of the Navigation Tree. These plots are very similar to the three 3-D radiation pattern plots. You can view them by clicking on their names in the navigation tree. The RCS values are expressed in m<sup>2</sup>. For visualization purposes, the 3-D plots are normalized to the maximum RCS value, which is also displayed in the legend box. The 2-D 2D RCS graphs can be plotted from [[EM.Cube|EM.CUBE]]'s the data manager exactly in the same way that you plot 2-D 2D radiation pattern graphs. A total of eight 2-D 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|EM.CUBE]] Libera 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 phi and theta 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. {{Note|Computing the 3-D mono-static RCS may take an enormous amount of computation time.}}
[[File:wire_pic50_tn{{Note|Computing the 3D mono-static RCS may take an enormous amount of computation time.png]]}}
Figure[[Image: A half-wave wire connected MORE.png|40px]] Click here to a metal plate illuminated by an obliquely incident plane wavelearn more about '''[[Data_Visualization_and_Processing#Visualizing_3D_RCS | Visualizing 3D RCS]]'''.
[[FileImage:wire_pic51_tnMORE.png|260px40px]] Click here to learn more about '''[[File:wire_pic52_tn.pngData_Visualization_and_Processing#2D_Radiation_and_RCS_Graphs |260pxPlotting 2D RCS Graphs]] [[File:wire_pic53_tn'''.png|260px]]
<table><tr><td> [[Image:wire_pic51_tn.png|thumb|300px|The RCS of the wire-a metal plate structure: (Left) σ<sub>θ</sub>, (Center) .]] </td><td> [[Image:wire_pic52_tn.png|thumb|300px|The RCS of a metal plate structure: σ<sub>φ</sub> and (Right) .]] </td><td> [[Image:wire_pic53_tn.png|thumb|300px|The total RCSof a metal plate structure: σ<sub>tot</sub>..]] </td></tr></table>
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