Changes

In order to analyze electromagnetic scattering from targets, you illuminate them with a plane wave source and compute the scattered (or reflected) fields. To define a plane wave source, right click on the <b>Plane Waves</b> item of the <b>Sources</b> section in the navigation tree and select <b>Insert New Source…</b> from the contextual menu. The Plane Wave Dialog opens up with a number of default settings. Your plane wave source will have an "Amplitude" of 1V/m and a zero "Phase". You will keep the default TM_z polarization. In the “Incident Angle” section of the dialog you need to enter the elevation &theta; and azimuth &phi; angles in the standard spherical coordinate system. Accept the default values: &theta; = 180&deg; andand &phi; = 0&deg;, which represent an X-polarized normally incident plane wave. Note that In [[EM.Cube]], plane waves are characterized by their unit propagation vector. Therefore, for a downward-looking normally incident plane wave, &theta; = 180&deg;, and for an upward looking wave (along the positive Z-axis), &theta; = 0&deg;. <table><tr><td>[[Image:Illumina_L1_Fig5insert.png|thumb|left|480px|Defining a plane wave source in EM.Illumina.]]</td></tr></table>

Next, you will define a Radar Cross Section (RCS) observable. Right-click on the <b>Radar Cross Sections</b> item in the navigation tree and select <b>Insert New RCS...</b> from the contextual menu. The Radar Cross Section dialog opens up. In the "RCS Type" section of the dialog, select the default '''Bistatic RCS''' option. Change the values of '''Observation Angle IncrementDefinition (deg)''' for both Theta and Phi from the default value of 5&deg; to 1&deg;, and close the dialog. This will set a very high angular resolution for both elevation and azimuth spherical observation angles.

[[Image:Illumina L1 Fig6.png|thumb|left|480px600px|The Radar Cross Section dialog.]]

Once the simulation is completed, the navigation tree is populated with simulation results under the current distributions and RCS nodes. [[EM.Cube]]’s computational modules usually generate two types of data: 2D and 3D. Examples of 2D data are Cartesian and polar radiation patterns. 2D data are graphed in <b>EM.Grid</b>. Examples of 3D data are near-field and current distributions and 3D radiation patterns. 3D data are visualized in [[EM.Cube]]’s project workspace, and the plots are usually overlaid on the physical structure. For this reason, it might be necessary to hide the geometric objects which might obstruct the plots. You can also freeze the geometric objects. In that case, you will see a wireframe outline of the frozen object and you cannot select it. To freeze an object, right-click on its surface in the project workspace or right-click on its name in the navigation tree and select '''Freeze''' from the contextual menu.

First, you will visualize the current distribution on the metal sphere. The "Current Distribution" section of the navigation tree plots both electric currents (J) and magnetic currents (M). Each current distribution observable contains a list of twelve amplitude and phase plots for all the six current components: J_x, J_y, J_z, and M_x, M_y, M_z. There are also two additional plots for the magnitude of total electric current and total magnetic current. In the case of your project, since you have only a PEC surface, <b>M</b> = 0. Click on any of these plots to display them in the project workspace. You can use the standard view operations such as dynamic zoom, rotate view, pan view, <i>etc</i>. to better examine these plots.

[[Image:Illumina L1 Fig10.png|thumb|left|640px720px|The intensity plot of the X-component of the electric surface current distribution.]]

[[Image:Illumina L1 Fig11.png|thumb|left|640px720px|The intensity plot of the Z-component of the electric surface current distribution.]]

[[Image:Illumina_L1_Fig13A_new.png|thumb|left|720px540px|The output plot settings dialog.]]

== Plotting 2D RCS Graphs in EM.Grid ==

Select the data files "RCS_1_RCS_Polar_YZ.CPX" and "RCS_1_RCS_Polar_ZX.CPX" from the list by clicking on their names and highlighting their rows in the table. You can make multiple selections using the {{key|Ctrl}} or {{key|Shift}} keys of your keyboard. Click the {{key|Plot}} button of the dialog to open EM.Grid, [[EM.Cube]]'s plotting utility. Two A PyPlot graph window pops up that shows the polar graphs appear in EM.Grid that show graph representing the RCS of your metallic target in the principal YZ and ZX planes.

[[Image:Illumina_L1_Fig17_new.png|thumb|left|720px||Settings data format to "dB_power_scale" in the graph properties Graph Settings dialog.]]

Close the graph properties dialog and return to the data manager. Do this for both graphs and then plot them in EM.Grid.

The 2D RCS graphs show both the theta and phi components as well as the total radar cross section. In the case of your spherical target, the "cross-pol" RCS is much smaller than the "co-pol" RCS. You can customize the EM.Grid graphsand change the scale of the graph axes. Click the "Edit Axes" tab on {{key|Graph Settings}} button and uncheck the left side bar of EM<b>Auto</b> box.Grid to open its settings panel. From the top dropFor X-down listAxis, select enter values -200 and 200 for <b>Min</b> and <b>Max</b>, respectively, and set the '''No. Major Intervals''' to 4 in "Left AxisSettings"panel. Set the minimum and maximum axis Similarly, for Y-Axis enter values to -10 and 5, 25, and 6 for <b>Min</b> and <b>Max</b>, and '''No. Major Intervals''' respectively. Make sure to click the button labeled {{key|Apply Above Changes}}. The dynamic range of your graph is now 35dB. In the "Interval/Increment" section of the settings, select the radio button labeled '''Number of Intervals''' and set it value equal to 730dB.

[[Image:Illumina L1 Fig18B.png|thumb|left|480px720px||EM.Grid's "Edit Axes" panelChanging X- and Y-axis scale in the Graph Settings dialog.]]

The Cartesian RCS graphs should now look like the figures below. The EM.Grid graphs are interactive. If you move the mouse around the graph, you can read the horizontal and vertical axis values of the graph each data point are displayed on EM.GridPlot's Status Bar. You can also track pan axes with left mouse or zoom with the data on the plots. Click the '''Track Selected Plot''' right mouse by clicking [[file:Grid track iconplot_pan_icon.png]] button of EM.GridPlot's top bottom toolbar. In this mode, a pair of crosshair lines appear on the graph that trace the data points on the selected plot. The horizontal and vertical axis values of each data point are displayed in the status bar.

[[Image:Illumina L1 Fig18A.png|thumb|left|480px||The 2D Cartesian graph of YZ-plane RCS plot of the PEC sphere with a normally incident TMz-polarized plane wave source (customized).]]

[[Image:Illumina L1 Fig19A.png|thumb|left|480px||The 2D Cartesian graph of ZX-plane RCS plot of the PEC sphere with a normally incident TMz-polarized plane wave source (customized).]]