Difference between revisions of "EM.Illumina"

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== An EM.Illumina Primer ==
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[[Image:Splash-po.jpg|right|720px]]
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<strong><font color="#bd5703" size="4">Fast Asymptotic Solver For Large-Scale Scattering Problems</font></strong>
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<table>
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<tr>
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<td>[[image:Cube-icon.png | link=Getting_Started_with_EM.Cube]] [[image:cad-ico.png | link=Building_Geometrical_Constructions_in_CubeCAD]] [[image:fdtd-ico.png | link=EM.Tempo]] [[image:prop-ico.png | link=EM.Terrano]] [[image:static-ico.png | link=EM.Ferma]] [[image:planar-ico.png | link=EM.Picasso]] [[image:metal-ico.png | link=EM.Libera]] </td>
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<tr>
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</table>
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[[Image:Tutorial_icon.png|30px]] '''[[EM.Cube#EM.Illumina_Documentation | EM.Illumina Tutorial Gateway]]'''
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[[Image:Back_icon.png|30px]] '''[[EM.Cube | Back to EM.Cube Main Page]]'''
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==Product Overview==
  
 
=== EM.Illumina in a Nutshell ===
 
=== EM.Illumina in a Nutshell ===
  
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EM.Illumina is a 3D electromagnetic simulator for modeling large free-space structures. It features a high frequency asymptotic solver based on Physical Optics (PO) for simulation of electromagnetic scattering from large metallic structures and impedance surfaces. You can use EM.Illumina to compute the radar cross section (RCS) of large target structures like aircraft or vehicles or simulate the radiation of antennas in the presence of large platforms.
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[[EM.Illumina]] is a 3D electromagnetic simulator for modeling large free-space structures. It features a high frequency asymptotic solver based on Physical Optics (PO) for simulation of electromagnetic scattering from large metallic structures and impedance surfaces. You can use [[EM.Illumina]] to compute the radar cross section (RCS) of large target structures like aircraft or vehicles or simulate the radiation of antennas in the presence of large platforms.
  
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EM.Illumina provides a computationally efficient alternative to full-wave solutions for extremely large structures when full-wave analysis becomes prohibitively expensive. Based on a high frequency asymptotic physical optics formulation, EM.Illumina assumes that a source like a short dipole radiator or an incident plane wave induces currents on a metallic structure, which in turn reradiate into the free space. In the case of an impedance surface, both surface electric and magnetic current are induced on the surface of the scatterer. A challenging step in establishing the PO currents is the determination of the lit and shadowed points on complex scatterer geometries. The conventional physical optics method (GO-PO) uses geometrical optics ray tracing from each source to the points on the scatterers to determine whether they fall into the lit or shadow regions. But this can become a time consuming task depending on the size of the computational problem. Besides GO-PO, EM.Illumina also offers a novel Iterative Physical Optics (IPO) formulation, which automatically accounts for multiple shadowing effects. The IPO technique can effectively capture dominant, near-field, multiple scattering effects from electrically large targets.
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[[EM.Illumina]] provides a computationally efficient alternative for extremely large structures when a full-wave solution becomes prohibitively expensive. Based on a high frequency asymptotic physical optics formulation, it assumes that an incident source generates currents on a metallic structure, which in turn reradiate into the free space. A challenging step in establishing the PO currents is the determination of the lit and shadowed points on complex scatterer geometries. Ray tracing from each source to the points on the scatterers to determine whether they are lit or shadowed is a time consuming task. To avoid this difficulty, [[EM.Illumina]]'s simulator uses a novel Iterative Physical Optics (IPO) formulation, which automatically accounts for multiple shadowing effects.The IPO technique can effectively capture dominant, near-field, multiple scattering effects from electrically large targets.
  
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=== Physical Optics as an Asymptotic Technique ===
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[[Image:Info_icon.png|30px]] Click here to lean more about the '''[[Basic Principles of Physical Optics | Theory of Physical Optics]]'''.
  
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Asymptotic methods are usually valid at high frequencies as <math>k_0 R = 2\pi R/\lambda_0 >> 1</math>, where R is the distance between the source and observation points, k<sub>0 </sub> is the free-space propagation constant and &lambda;<sub>0 </sub>is the free-space wavelength. Under such conditions, electromagnetic fields and waves start to behave more like optical fields and waves. Asymptotic methods are typically inspired by optical analysis. Two important examples of asymptotic methods are the Shoot-and-Bounce-Rays (SBR) method and Physical Optics (PO). The [[SBR Method|SBR method]] is a ray tracing method based on Geometrical Optics (GO) and forms the basis of the simulation engine of [[EM.Terrano]].
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<table>
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<tr>
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In the Physical Optics (PO) method, a scatterer surface is illuminated by an incident source, and it is modeled by equivalent electric and magnetic surface currents. This concept is based on the fundamental equivalence theorem of electromagnetics and the Huygens principle. The electric surface currents are denoted by '''J(r)''' and the magnetic surface currents are denoted by '''M(r)''', where '''r''' is the position vector. According to the Huygens principle, the equivalent electric and magnetic surface currents are derived from the tangential components of magnetic and electric fields on a given surface, respectively. This will be discussed in more detail in the next sections. In a conventional PO analysis, which involves only perfect electric conductors, only electric surface currents related to the tangential magnetic fields are considered. 
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<td>  
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[[Image:Illumina L2 Fig title.png|thumb|left|420px|Analyzing scattering from a trihedral corner reflector using IPO solver.]]
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Click here to lean more about the '''[[Theory of Physical Optics]]'''.
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</td>
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</tr>
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</table>
  
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== Building & Discretizing the Physical Structure ==
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=== EM.Illumina as the Physical Optics Module of EM.Cube ===
  
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[[Image:PO18(1).png|thumb|250px|EM.Illumina's Navigation Tree.]]
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[[EM.Illumina]] is the high-frequency, asymptotic '''Physical Optics Module''' of '''[[EM.Cube]]''', a comprehensive, integrated, modular electromagnetic modeling environment. [[EM.Illumina]] shares the visual interface, 3D parametric CAD modeler, data visualization tools, and many more utilities and features collectively known as [[Building_Geometrical_Constructions_in_CubeCAD | CubeCAD]] with all of [[EM.Cube]]'s other computational modules.
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=== Grouping Objects By Surface Type ===
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EM.Illumina organizes physical objects by their surface type. Any object in EM.Illumina is assumed to be made of one of the three surface types:
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[[EM.Illumina]]'s simulator is seamlessly interfaced with [[EM.Cube|EM.CUBE]]'s other simulattion engines. This module is the ideal place to define Huygens sources. These are based on Huygens surface data that are generated using a full-wave simulator like [[EM.Tempo]], [[EM.Picasso]] or [[EM.Libera]].
  
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# '''Perfect Electric Conductor (PEC)'''
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Getting_Started_with_EM.Cube | EM.Cube Modeling Environment]]'''.
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# '''Perfect Magnetic Conductor (PMC)'''
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# '''Generalized Impedance Surface'''
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EM.Illumina can only handle surface and solid CAD objects. No line or [[Curve Objects|curve objects]] are allowed in the project workspace; or else, they will be ignored during the PO simulation. You can define several PEC, PMC or impedance surface groups with different colors and impedance values. All the objects created and drawn under a group share the same color and other properties.
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=== Advantages & Limitations of EM.Illumina's PO Solver ===
  
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A new surface group can be defined by simply right clicking on one of the three '''PEC''', '''PMC''' or '''Impedance Surface''' items in the '''Physical Structure''' section of the navigation tree and selecting '''Insert New PEC...''', '''Insert New PMC...''', or '''Insert New Impedance Surface...''' from the contextual menu. A dialog for setting up the group properties opens up. In this dialog you can change the name of the group or its color. In the case of a surface impedance group, you can set the values for the real and imaginary parts of the '''Surface Impedance''' in Ohms.  
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[[EM.Illumina]] provides a computationally efficient alternative to full-wave solutions for extremely large structures when full-wave analysis becomes prohibitively expensive. For simple scatterer geometries, [[EM.Illumina]]'s GO-PO solver is fairly adequate. But for complex geometries that involve multiple shadowing effects, the IPO solver must be utilized. The IPO technique can effectively capture dominant, near-field, multiple scattering effects from electrically large targets with concave surfaces. You have to remember that Physical Optics is a surface simulator. This is not a problem for PEC and PMC objects, which have zero internal fields, or even impedance surfaces, where you can satisfy the boundary conditions on one side of a surface only. PO analysis cannot handle the fields inside dielectric objects. Additionally, most coupling effects between adjacent scatterers are ignored.
  
 
<table>
 
<table>
 
<tr>
 
<tr>
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<td> [[Image:PO19.png|thumb|250px|The PEC dialog.]] </td>
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<td>  
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<td> [[Image:PO20.png|thumb|250px|The PMC dialog.]] </td>
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[[Image:PO Ship Pattern.png|thumb|left|550px|Computed radiation pattern of a short dipole radiator over a large metallic battleship.]]
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<td> [[Image:PO21.png|thumb|250px|The Impedance Surface dialog.]] </td>
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</td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
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=== Creating New Objects &amp; Moving Them Around ===
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== EM.Illumina Features at a Glance ==
  
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[[Image:PO22(1).png|thumb|400px|Moving objects among different surface groups in EM.Illumina.]]
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=== Structure Definition ===
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The objects that you draw in [[EM.Cube]]'s project workspace always belong to the &quot;Active&quot; surface group. By default, the last object group that you created remains active until you change it. The current active group is always listed in bold letters in the Navigation Tree. Any surface group can be made active by right clicking on its name in the Navigation Tree and selecting the '''Activate''' item of the contextual menu. If you start a new [[PO Module]] project and draw any object without having previously defined a surface group, a default PEC group is automatically created and added to the Navigation Tree to hold your new object.
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You can move one or more selected objects to any material group. Right click on the highlighted selection and select '''Move To &gt; Physical Optics &gt;''' from the contextual menu. This opens another sub-menu with a list of all the available surface groups already defined in [[PO Module]]. Select the desired surface group, and all the selected objects will move to that group. The objects can be selected either in the project workspace, or their names can be selected from the Navigation Tree. In the latter case, make sure that you hold the keyboard's '''Shift Key''' or '''Ctrl Key''' down while selecting a material group's name from the contextual menu. You can also move one or more objects from a PO surface group to [[EM.Cube]]'s other modules, or vice versa. In that case, the sub-[[menus]] of the '''Move To &gt;''' item of the contextual menu will indicate all the [[EM.Cube]] modules that have valid groups for transfer of the selected objects.
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<ul>
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<li>
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Metal (PEC) solids and surfaces in free space</li>
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<li>
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PMC and impedance surfaces in free space</li>
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<li>
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Import STL CAD files as native polymesh structures</li>
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<li>
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Huygens blocks imported from full-wave modules</li>
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</ul>
  
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{{Note|In [[EM.Cube]], you can import external CAD models (such as STEP, IGES, STL models, etc.) only to [[CubeCAD]]. From [[CubeCAD]], you can then move the imported objects to any other computational module including [[PO Module]].}}
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=== Sources ===
  
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=== Generating &amp; Customizing PO Mesh ===
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<ul>
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<li>
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Short dipoles</li>
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<li>
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Import previously generated wire mesh solution as collection of short dipoles</li>
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<li>
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Plane wave excitation with linear and circular polarizations</li>
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<li>
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Multi-ray excitation capability (ray data imported from [[EM.Terrano]] or external files)</li>
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<li>
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Huygens sources imported from PO or other modules with arbitrary rotation and array configuration</li>
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</ul>
  
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[[File:PO23.png|thumb|250px|[[PO Module]]'s Mesh Settings dialog]]
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=== Mesh Generation ===
  
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The mesh generation process in [[PO Module]] involves three steps:
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<ul>
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<li>
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Surface triangular mesh with control over tessellation parameters</li>
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<li>
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Local mesh editing of polymesh objects</li>
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</ul>
  
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# Setting the mesh properties.
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=== Physical Optics Simulation ===
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# Generating the mesh.
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# Verifying the mesh.
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The objects of your physical structure are meshed based on a specified mesh density expressed in cells/&lambda;<sub>0</sub>. The default mesh density is 20 cells/&lambda;<sub>0</sub>. To view the PO mesh, click on the [[File:mesh_tool_tn.png]] button of the '''Simulate Toolbar''' or select '''Menu &gt; Simulate &gt; Discretization &gt; Show Mesh''' or use the keyboard shortcut '''Ctrl+M'''. When the PO mesh is displayed in the project workspace, [[EM.Cube]]'s mesh view mode is enabled. In this mode, you can perform view operations like rotate view, pan, zoom, etc. However, you cannot select or move or edit objects. While the mesh view is enabled, the '''Show Mesh''' [[File:mesh_tool.png]] button remains depressed. To get back to the normal view or select mode, click this button one more time, or deselect '''Menu &gt; Simulate &gt; Discretization &gt; Show Mesh''' to remove its check mark or simply click the '''Esc Key''' of the keyboard.
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<ul>
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<li>
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Physical Optics solution of metal scatterers and impedance surfaces</li>
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<li>
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Conventional Geometrical Optics - Physical Optics (GOPO) solver</li>
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<li>
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Novel iterative PO solver for fast simulation of multiple shadowing effects and multi-bounce reflections</li>
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<li>
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Calculation of near fields, far fields and scattering cross section (bistatic and monostatic RCS)</li>
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<li>
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Frequency and angular sweeps with data animation</li>
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<li>
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Parametric sweep with variable object properties or source parameters</li>
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<li>
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Multi-variable and multi-goal optimization of structure</li>
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<li>
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Remote simulation capability</li>
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<li>
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Both Windows and Linux versions of PO simulation engine available</li>
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</ul>
  
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&quot;Show Mesh&quot; generates a new mesh and displays it if there is none in the memory, or it simply displays an existing mesh in the memory. This is a useful feature because generating a PO mesh may take a long time depending on the complexity and size of objects. If you change the structure or alter the mesh settings, a new mesh is always generated. You can ignore the mesh in the memory and force [[EM.Cube]] to generate a mesh from the ground up by selecting '''Menu &gt; Simulate &gt; Discretization &gt; Regenerate Mesh''' or by right clicking on the '''3-D Mesh''' item of the Navigation Tree and selecting '''Regenerate''' from the contextual menu.
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=== Data Generation &amp; Visualization ===
  
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To set the PO mesh properties, click on the [[File:mesh_settings.png]] button of the '''Simulate Toolbar''' or select '''Menu &gt; Simulate &gt; Discretization &gt; Mesh Settings... '''or right click on the '''3-D Mesh''' item in the '''Discretization''' section of the Navigation Tree and select '''Mesh Settings...''' from the contextual menu, or use the keyboard shortcut '''Ctrl+G'''. You can change the value of '''Mesh Density''' to generate a triangular mesh with a higher or lower resolutions. [[PO Module]] offers two algorithms for triangular mesh generation. The default algorithm is '''Regular Surface Mesh''', which creates triangular elements that have almost equal edge lengths. The other algorithm is '''Structured Surface Mesh''', which usually creates a very structured mesh with a large number of aligned triangular elements. You can change the mesh generation algorithm from the dropdown list labeled '''Mesh Type'''. Another parameter that can affect the shape of the mesh especially in the case of [[Solid Objects|solid objects]] is the '''Curvature Angle Tolerance''' expressed in degrees. This parameter determines the apex angle of the triangular cells of the structured mesh. Lower values of the angle tolerance will results in more pointed triangular cells.
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<ul>
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<li>
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Electric and magnetic surface current distributions on metallic or impedance surfaces</li>
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<li>
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Near field intensity plots (vectorial - amplitude &amp; phase)</li>
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<li>
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Huygens surface data generation for use in PO or other [[EM.Cube]] modules</li>
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<li>
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Far field radiation patterns: 3D pattern visualization and 2-D Cartesian and polar graphs</li>
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<li>
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Bi-static and monostatic radar cross section: 3D visualization and 2D graphs</li>
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<li>
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Custom output parameters defined as mathematical expressions of standard outputs</li>
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</ul>
  
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=== More On Triangular Surface Mesh ===
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== Building the Physical Structure in EM.Illumina ==
  
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The physical optics method assumes an unbounded, open-boundary computational domain, wherein the physical structure is placed against a free space background medium. As such, only finite-extent surfaces are discretized. [[EM.Cube]]'s [[PO Module]] uses a triangular surface mesh to discretize all the surface and [[Solid Objects|solid objects]] in the project workspace. As mentioned earlier, [[Curve Objects|curve objects]] (or wires) are not allowed in [[PO Module]]. In the case of solids, only the surface of the object or its faces are discretized, as the interior volume is not taken into account in a PO analysis. In general, triangular cells are placed on the exterior surface of [[Solid Objects|solid objects]]. In contrast, [[Surface Objects|surface objects]] are assumed to be double-sided by default. The means that the PO mesh of a surface object indeed consists of coinciding double cells, one representing the upper or positive side and the other representing the lower or negative side. This may lead to a very large number of cells. [[EM.Cube]]'s PO mesh has some more settings that allow you to treat all mesh cells as double-sided or all single-sided. This can be done in the Mesh Settings dialog by checking the boxes labeled '''All Double-Sided Cells''' and '''All Single-Sided Cells'''. This is useful when your project workspace contains well-organized and well-oriented [[Surface Objects|surface objects]] only. In the single-sided case, it is very important that all the normals to the cells point towards the source. Otherwise, the [[Surface Objects|surface objects]] will be assumed to lie in the shadow region and no currents will be computed on them. By checking the box labeled '''Reverse Normal''', you instruct [[EM.Cube]] to reverse the direction of the normal vectors at the surface of all the cells.
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=== The Variety of Surface Types in EM.Illumina ===
  
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[[File:PO24.png]]
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[[EM.Illumina]] organizes physical objects by their surface type. Any object in [[EM.Illumina]] is assumed to be made of one of the three surface types:
  
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Figure: Forcing mesh cells to be single-sided in a PO simulation.
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{| class="wikitable"
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|-
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! scope="col"| Icon
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! scope="col"| Material Type
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! scope="col"| Applications
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! scope="col"| Geometric Object Types Allowed
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|-
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| style="width:30px;" | [[File:pec_group_icon.png]]
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| style="width:250px;" | [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Perfect Electric Conductor (PEC) |Perfect Electric Conductor (PEC) Surface]]
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| style="width:300px;" | Modeling perfect metal surfaces
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| style="width:250px;" | Solid and surface objects
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|-
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| style="width:30px;" | [[File:pmc_group_icon.png]]
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| style="width:250px;" | [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Perfect Magnetic Conductor (PMC) |Perfect Magnetic Conductor (PMC) Surface]]
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| style="width:300px;" | Modeling perfect magnetic surfaces
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| style="width:250px;" | Solid and surface objects
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|-
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| style="width:30px;" | [[File:voxel_group_icon.png]]
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| style="width:250px;" | [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Impedance Surface |Impedance/Dielectric Surface]]
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| style="width:300px;" | Modeling impedance surfaces as an equivalent to the surface of dielectric objects
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| style="width:250px;" | Solid and surface objects
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|-
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| style="width:30px;" | [[File:Virt_group_icon.png]]
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| style="width:250px;" | [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Virtual_Object_Group | Virtual Object]]
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| style="width:300px;" | Used for representing non-physical items 
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| style="width:250px;" | All types of objects
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|}
  
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'''As a general rule, [[EM.Cube]]'s PO mesh generator merges all the objects that belong to the same surface group using the Boolean Union operation.''' As a result, overlapping objects are transformed into a single consolidated object. This is particularly important for generating a contiguous and consistent mesh in the transition and junction areas between connected objects. In general, objects of the same CAD category can be &quot;unioned&quot;. For example, [[Surface Objects|surface objects]] can be merged together, and so can [[Solid Objects|solid objects]]. However, a surface object and a solid in general do not merge. Objects that belong to different groups on the Navigation Tree are not merged during mesh generation even if they are all of PEC type and physically overlap.
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Click on each category to learn more details about it in the [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types]].
  
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[[File:PO25.png|400px]] [[File:PO26.png|400px]]
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[[EM.Illumina]] can only handle surface and solid CAD objects. Only the outer surface of solid objects is considered in the PO simulation. No line or curve objects are allowed in the project workspace; or else, they will be ignored during the PO simulation.
  
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Figure: Geometry and PO mesh of an overlapping sphere and ellipsoid.
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=== Organizing Geometric Objects by Surface Type ===
  
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=== Mesh Density &amp; Local Mesh Control ===
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You can define several PEC, PMC or impedance surface groups with different colors and impedance values. All the objects created and drawn under a group share the same color and other properties. Once a new surface node has been created on the navigation tree, it becomes the "Active" surface group of the project workspace, which is always listed in bold letters. When you draw a new CAD object such as a Box or a Sphere, it is inserted under the currently active surface type. There is only one surface group that is active at any time. Any surface type can be made active by right clicking on its name in the navigation tree and selecting the '''Activate''' item of the contextual menu. It is recommended that you first create surface groups, and then draw new objects under the active surface group. However, if you start a new EM.Illumina project from scratch, and start drawing a new object without having previously defined any surface groups, a new default PEC surface group is created and added to the navigation tree to hold your new CAD object.
  
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[[Image:PO31.png|thumb|400px|Locking the mesh density of a PEC group.]]
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[[Image:Info_icon.png|30px]] Click here to learn more about '''[[Building Geometrical Constructions in CubeCAD#Transferring Objects Among Different Groups or Modules | Moving Objects among Different Groups]]'''.
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[[Image:PO32.png|thumb|400px|Triangular surface mesh of two PEC box objects with the orange PEC group having a locked mesh of higher density.]]
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EM.Illumina applies the mesh density specified in the Mesh Settings dialog on a global scale to discretize all the objects in the project workspace. Although the mesh density is expressed in cells per free space wavelength similar to full-wave method of moments (MoM) solvers, you have to keep in mind that the triangular surface mesh cells in PO Modules act slightly differently. The complex-valued, vectorial, electric and magnetic surface currents, '''J''' and '''M''' are assumed to be constant on the surface of each triangular cell. On plates and flat faces or surfaces, the normal vectors to all the cells are identical. Incident plane waves or other types of relatively uniform source fields induce uniform PO currents on all these cells. Therefore, a high resolution mesh may not be necessary on flat surface or faces. However, a high mesh density is very important for accurate discretization of curved objects like spheres or ellipsoids.      
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You can lock the mesh density of any surface group to any desired value different than the global mesh density. To do so, open the property dialog of a surface group by right clicking on its name in the Navigation Tree and select '''Properties...''' from the contextual menu. At the bottom of the dialog, check the box labeled '''Lock Mesh'''. This will enable the '''Density '''box, where you can set a desired value. The default value is equal to the global mesh density.
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{{Note|In [[EM.Cube]], you can import external CAD models (such as STEP, IGES, STL models, etc.) only to CubeCAD. From CubeCAD, you can then move the imported objects to EM.Illumina.}}
  
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== Excitation Sources ==
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<table>
 +
<tr>
 +
<td> [[File:PO MAN1.png|thumb|left|480px|EM.Illumina's navigation tree.]] </td>
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</tr>
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</table>
  
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=== Hertzian Dipole Sources ===
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== EM.Illumina's Excitation Sources ==
  
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[[File:PO30.png|thumb|300px|PO Module's Short Dipole Source dialog]]
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[[EM.Illumina]] provides three types of sources for the excitation of your physical optics simulation:
  
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A short dipole is the simplest way of exciting a structure in [[EM.Cube]]'s [[PO Module]]. A short dipole source acts like an infinitesimally small ideal current source. To define a short dipole source, follow these steps:
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{| class="wikitable"
 +
|-
 +
! scope="col"| Icon
 +
! scope="col"| Source Type
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! scope="col"| Applications
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! scope="col"| Restrictions
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|-
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| style="width:30px;" | [[File:hertz_src_icon.png]]
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| [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Hertzian Short Dipole Source |Hertzian Short Dipole Source]]
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| style="width:300px;" | Almost omni-directional physical radiator
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| style="width:300px;" | None, stand-alone source
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|-
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| style="width:30px;" | [[File:plane_wave_icon.png]]
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| [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Plane Wave |Plane Wave Source]]
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| style="width:300px;" | Used for modeling scattering
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| style="width:300px;" | None, stand-alone source
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|-
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| style="width:30px;" | [[File:huyg_src_icon.png]]
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| [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types#Huygens Source |Huygens Source]]
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| style="width:300px;" | Used for modeling equivalent sources imported from other [[EM.Cube]] modules
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| style="width:300px;" | Imported from a Huygens surface data file
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|}
  
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* Right click on the '''Short Dipoles''' item in the '''Sources''' section of the Navigation Tree and select '''Insert New Source...''' from the contextual menu. The Short Dipole dialog opens up.
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Click on each category to learn more details about it in the [[Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types]].
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* In the '''Source Location''' section of the dialog, you can set the coordinate of the center of the short dipole. By default, the source is placed at the origin of the world coordinate system at (0,0,0). You can type in new coordinates or use the spin buttons to move the dipole around.
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* In the '''Source Properties''' section, you can specify the '''Amplitude''' in Volts, the '''Phase''' in degrees as well as the '''Length''' of the dipole in project units.
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* In the '''Direction Unit Vector''' section, you can specify the orientation of the short dipole by setting values for the components '''uX''', '''uY''', and '''uZ''' of the dipole's unit vector. The default values correspond to a vertical (Z-directed) short dipole. The dialog normalizes the vector components upon closure even if your component values do not satisfy a unit magnitude.
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=== Importing Short Dipoles From MoM3D Module ===
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A short Hertzian dipole is the simplest way of exciting a structure in [[EM.Illumina]]. A short dipole source acts like an infinitesimally small ideal current source. The total radiated power by your dipole source is calculated and displayed in Watts in its property dialog. Your physical structure in [[EM.Illumina]] can also be excited by an incident plane wave. In particular, you need a plane wave source to compute the radar cross section of a target. The direction of incidence is defined by the &theta; and &phi; angles of the unit propagation vector in the spherical coordinate system. The default values of the incidence angles are &theta; = 180° and &phi; = 0° corresponding to a normally incident plane wave propagating along the -Z direction with a +X-polarized E-vector. Huygens sources are virtual equivalent sources that capture the radiated electric and magnetic fields from another structure that was previously analyzed in another [[EM.Cube]] computational module.
  
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The solution of a problem in one of [[EM.Cube]]'s computational modules can serve as the excitation source for another problem in another computational module. An example of this is analyzing a wire antenna in the [[MoM3D Module]] and importing the wire current solution to [[PO Module]] to excite a large scatterer. Remember that you cannot define wires or [[Curve Objects|curve objects]] in [[PO Module]]. However, you can have short dipole sources that act like differential wire elements carrying fixed currents. Using this concept, you can realize a complex wire antenna or radiator array as the source of your PO project. 
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== EM.Illumina's Simulation Data & Observables ==
  
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When you simulate a wire structure in the [[MoM3D Module]], you can define a '''Current Distribution Observable''' in your project. This is used not only to visualize the current distribution in the project workspace, but also to save the current solution into an ASCII data file. This data file is called &quot;MoM.IDI&quot; by default and has a '''.IDI''' file extension. The current data are saved as line segments representing each of the wire cells together with the complex-valued, vectorial current at the center of each cell. You can import the current data from an existing '''.IDI''' file to [[PO Module]], To import a wire current solution, right click on '''Short Dipoles''' item in the '''Sources''' section of the Navigation Tree and select '''Import Dipole Source...''' from the contextual menu. This opens up the standard [[Windows]] Open dialog with the file type set to '''.IDI'''. Browse your folders to find the right current data file. Once you find it, select it and click the '''Open''' button of the dialog. This will create as many short dipole sources on the [[PO Module]]'s Navigation Tree as the total number of mesh cells in the Wire MoM solution. From this point on, each of the imported dipoles behave like a regular short dipole source. You can open the property dialog of each individual source and modify its [[parameters]], if necessary.
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[[EM.Illumina]] does not produce any output data on its own unless you define one or more observables for your simulation project. The primary output data in the Physical Optics method are the electric and magnetic surface current distributions on the surface of your structure. At the end of a PO simulation, [[EM.Illumina]] generates a number of output data files that contain all the computed simulation data. Once the current distributions are known, [[EM.Illumina]] can compute near-field distributions as well as far-field quantities such as radiation patterns and radar cross section (RCS).  
  
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[[File:PO36.png|800px]]
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[[EM.Illumina]] currently provides the following observables:
  
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Figure: Importing a Wire MoM current solution into the [[PO Module]]. In this structure, 90 wire cell currents representing a helical antenna were imported and placed above a large sinusoidal PEC surface.
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{| class="wikitable"
 +
|-
 +
! scope="col"| Icon
 +
! scope="col"| Simulation Data Type
 +
! scope="col"| Observable Type
 +
! scope="col"| Applications
 +
! scope="col"| Restrictions
 +
|-
 +
| style="width:30px;" | [[File:currdistr_icon.png]]
 +
| style="width:150px;" | Current Distribution Maps
 +
| style="width:150px;" | [[Glossary of EM.Cube's Simulation Observables & Graph Types#Current Distribution |Current Distribution]]
 +
| style="width:300px;" | Computing electric surface current distribution on PEC and impedance surfaces and magnetic surface current distribution on PMC and impedance surfaces
 +
| style="width:250px;" | None
 +
|-
 +
| style="width:30px;" | [[File:fieldsensor_icon.png]]
 +
| style="width:150px;" | Near-Field Distribution Maps
 +
| style="width:150px;" | [[Glossary of EM.Cube's Simulation Observables & Graph Types#Near-Field Sensor |Near-Field Sensor]]
 +
| style="width:300px;" | Computing electric and magnetic field components on a specified plane in the frequency domain
 +
| style="width:250px;" | None
 +
|-
 +
| style="width:30px;" | [[File:farfield_icon.png]]
 +
| style="width:150px;" | Far-Field Radiation Characteristics
 +
| style="width:150px;" | [[Glossary of EM.Cube's Simulation Observables & Graph Types#Far-Field Radiation Pattern |Far-Field Radiation Pattern]]
 +
| style="width:300px;" | Computing the radiation pattern and additional radiation characteristics such as directivity, axial ratio, side lobe levels, etc.
 +
| style="width:250px;" | None
 +
|-
 +
| style="width:30px;" | [[File:rcs_icon.png]]
 +
| style="width:150px;" | Far-Field Scattering Characteristics
 +
| style="width:150px;" | [[Glossary of EM.Cube's Simulation Observables & Graph Types#Radar Cross Section (RCS) |Radar Cross Section (RCS)]]
 +
| style="width:300px;" | Computing the bistatic and monostatic RCS of a target
 +
| style="width:250px;" | Requires a plane wave source
 +
|-
 +
| style="width:30px;" | [[File:huyg_surf_icon.png]]
 +
| style="width:150px;" | Equivalent electric and magnetic surface current data
 +
| style="width:150px;" | [[Glossary of EM.Cube's Simulation Observables & Graph Types#Huygens Surface |Huygens Surface]]
 +
| style="width:300px;" | Collecting tangential field data on a box to be used later as a Huygens source in other [[EM.Cube]] modules
 +
| style="width:250px;" | None
 +
|}
  
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=== Plane Wave Sources ===
+
Click on each category to learn more details about it in the [[Glossary of EM.Cube's Simulation Observables & Graph Types]].
  
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[[File:PO29.png|thumb|300px|PO Module's Plane Wave dialog]]
+
Current distributions are visualized on the surface of PO mesh cells, and the magnitude and phase of the electric and magnetic surface currents are plotted for all the objects. A single current distribution node in the navigation tree holds the current distribution data for all the objects in the project workspace. Since the currents are plotted on the surface of the individual mesh cells, some parts of the plots may be blocked by and hidden inside smooth and curved objects. To be able to view those parts, you may have to freeze the obstructing objects or switch to the mesh view mode.
  
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Your physical structure in [[PO Module]] can be excited by an incident plane wave. In particular, a plane wave source can be used to compute the radar cross section of a target. A plane wave is defined by its propagation vector indicating the direction of incidence and its polarization. [[EM.Cube]]'s [[PO Module]] provides the following polarization options: TMz, TEz, Custom Linear, LCPz and RCPz.
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<table>
 +
<tr>
 +
<td> [[Image:PO38.png|thumb|390px|The current distribution plot of a PEC sphere illuminated by an obliquely incident plane wave.]] </td>
 +
</tr>
 +
</table>
  
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The direction of incidence is defined through the &theta; and &phi; angles of the unit propagation vector in the spherical coordinate system. The values of these angles are set in degrees in the boxes labeled '''Theta''' and '''Phi'''. The default values are &theta; = 180° and &phi; = 0° representing a normally incident plane wave propagating along the -Z direction with a +X-polarized E-vector. In the TM<sub>z</sub> and TE<sub>z</sub> polarization cases, the magnetic and electric fields are parallel to the XY plane, respectively. The components of the unit propagation vector and normalized E- and H-field vectors are displayed in the dialog. In the more general case of custom linear polarization, besides the incidence angles, you have to enter the components of the unit electric '''Field Vector'''. However, two requirements must be satisfied: '''ê . ê''' = 1 and '''ê × k''' = 0 . This can be enforced using the '''Validate''' button at the bottom of the dialog. If these conditions are not met, an error message is generated. The left-hand (LCP) and right-hand (RCP) circular polarization cases are restricted to normal incidences only (&theta; = 180°).
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[[EM.Illumina]] allows you to visualize the near fields at a predefined field sensor plane of arbitrary dimensions. Calculation of near fields is a post-processing process and may take a considerable amount of time depending on the resolution that you specify.  
  
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To define a plane wave source follow these steps:
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{{Note|Keep in mind that since Physical Optics is an asymptotic method, the field sensors must be placed at adequate distances (at least one or few wavelengths) away from the scatterers to produce acceptable results.}}
  
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* Right click on the '''Plane Waves''' item in the '''Sources''' section of the Navigation Tree and select '''Insert New Source...''' The Plane wave Dialog opens up.
+
<table>
−
* In the Field Definition section of the dialog, you can enter the '''Amplitude''' of the incident electric field in V/m and its '''Phase''' in degrees. The default field Amplitude is 1 V/m with a zero Phase.
+
<tr>
−
* The direction of the Plane Wave is determined by the incident '''Theta''' and '''Phi''' angles in degrees. You can also set the '''Polarization''' of the plane wave and choose from the five options described earlier. When the '''Custom Linear''' option is selected, you also need to enter the X, Y, Z components of the '''E-Field Vector'''.
+
<td> </td>
 +
<td> [[Image:PO43.png|thumb|360px|Electric field distribution on a sensor plane above a metallic sphere.]] </td>
 +
<td> [[Image:PO44.png|thumb|360px|Magnetic field distribution on a sensor plane above a metallic sphere.]] </td>
 +
</tr>
 +
</table>
  
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=== Huygens Sources ===
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You need to define a far field observable if you want to plot the radiation patterns of your physical structure. After a PO simulation is finished, three 3D radiation patterns plots are displayed in the project workspace and are overlaid on your physical structure. These are the Theta and Phi components of the far-zone electric fields as well as the total far field.
  
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[[File:po_phys17.png|thumb|300px|PO Module's Huygens Source dialog]]
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{{Note| The 3D radiation pattern is always displayed at the origin of the spherical coordinate system, (0,0,0), with respect to which the far radiation zone is defined. Oftentimes, this might not be the radiation center of your physical structure.}}
  
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At the end of a full-wave simulation in the [[EM.Cube]]'s FDTD, MoM3D, Planar or Physical Optics Modules, you can generate Huygens surface data. According to Huygens' principle, if one knows the tangential electric and magnetic field components on a closed surface, one can determine the total electric and magnetic fields everywhere inside and outside that closed surface. Huygens surfaces are defined around a structure for recording the tangential components of electric and magnetic fields at the end of full-wave simulation of the structure. The tangential electric and magnetic fields are saved into ASCII data files as magnetic and electric currents, respectively. These current can be used as excitation for other structures. In other words, the electric and magnetic currents associated with a Huygens source radiate energy and provide the excitation for the [[PO Module]]'s physical structure.
+
<table>
 +
<tr>
 +
<td> [[Image:PO46.png|thumb|360px|3D radiation pattern of a parabolic dish reflector excited by a short dipole at its focal point.]] </td>
 +
</tr>
 +
</table>
  
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In order to define a Huygens source, you need to have a Huygens data file of '''.HUY''' type. This file is generated as an output data file at the end of an FDTD, MoM3D, Planar or PO simulation, if you have defined a Huygens  Surface observable in one of those projects. When you define a Huygens source, you indeed import an existing Huygens surface into the project and set it as an excitation source.
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When your physical structure is excited by a plane wave source, the calculated far field data indeed represent the scattered fields. [[EM.Illumina]] can calculate 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 &theta;<sub>0</sub> and &phi;<sub>0</sub>, and the RCS is measured and plotted at all &theta; and &phi; angles. In mono-static RCS, the structure is illuminated by a plane wave at incidence angles &theta;<sub>0</sub> and &phi;<sub>0</sub>, and the RCS is measured and plotted at the echo angles 180°-&theta;<sub>0</sub>; and &phi;<sub>0</sub>. It is clear that in the case of mono-static RCS, the PO simulation engine runs an internal angular sweep, whereby the values of the plane wave incidence angles &theta; and &phi; are varied over the entire intervals [0°, 180°] and [0°, 360°], respectively, and the backscatter RCS is recorded.
  
−
To create a new Huygens source, follow these steps:
+
To calculate RCS, first you have to define an RCS observable instead of a radiation pattern. At the end of a PO simulation, the thee RCS plots &sigma;<sub>&theta;</sub>, &sigma;<sub>&phi;</sub>, and &sigma;<sub>tot</sub> are added under the far field section of the navigation tree. Keep in mind that computing the 3D mono-static RCS may take an enormous amount of computation time.
  
−
* Right click on the '''Huygens Sources''' item in the '''Sources''' section of the Navigation Tree and select '''Import Huygens Source...''' from the contextual menu.
+
{{Note| The 3D RCS plot is always displayed at the origin of the spherical coordinate system, (0,0,0), with respect to which the far radiation zone is defined. Oftentimes, this might not be the scattering center of your physical structure.}}
−
* The standard [[Windows]] Open Dialog opens up. The file type is set to '''.HUY''' by default. Browse your folders to find a Huygens surface data file with a '''.HUY''' file extension. Select the file and click the '''Open''' button of the dialog to import the data.
+
−
* Once imported, the Huygens source appears in the Project Workspace as a wire-frame box.
+
−
* You can open the property dialog of a Huygens source by right clicking on its name in the Navigation Tree and selecting '''Properties...''' From this dialog you can change the color of the Huygens source box as well as its location and orientation. You can enter new values for the X, Y, Z '''Center Coordinates''' and '''Rotation Angles''' of the Huygens box. You can also view the dimensions of the box.
+
−
* By default, the Huygens data are imported as a single Huygens source. You can create an arbitrary array of Huygens sources for your PO project. To do so, in the &quot;Create Array&quot; section of the Huygens source dialog, enter desired values for the '''Number of Elements''' and '''Element Spacing''' along the X, Y and Z directions. You will see an array of wire-frame box appear in the project workspace.
+
  
−
[[File:PO34.png|400px]] [[File:PO35.png|400px]]
+
<table>
 +
<tr>
 +
<td> [[Image:PO48.png|thumb|420px|RCS of a PEC sphere illuminated by an laterally incident plane wave.]] </td>
 +
</tr>
 +
</table>
  
−
Figure: (Left) A rotated imported Huygens source, and (Right) An array of imported Huygens sources defined to excite a PEC box.
+
== Discretizing the Physical Structure in EM.Illumina ==
  
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== Running PO Simulations ==
+
EM.Illumina uses a triangular surface mesh to discretize the structure of your project workspace. The mesh generating algorithm tries to generate regularized triangular cells with almost equal surface areas across the entire structure. You can control the cell size using the "Mesh Density" parameter. By default, the mesh density is expressed in terms of the free-space wavelength. The default mesh density is 10 cells per wavelength. In the Physical Optics method, the electric and magnetic surface currents, '''J''' and '''M''', are assumed to be constant on the surface of each triangular cell. On flat surfaces, the unit normal vectors to all the cells are identical. Incident plane waves or other relatively uniform source fields induce uniform PO currents on all these cells. Therefore, a high resolution mesh may not be necessary on flat surface or faces. Accurate discretization of curved objects like spheres or ellipsoids, however, requires a high mesh density.     
 +
 +
<table>
 +
<tr>
 +
<td>
 +
[[File:PO4.png|thumb|left|480px|EM.Illumina's Mesh Settings dialog.]]
 +
</td>
 +
</tr>
 +
</table>
  
−
=== Running A Basic PO Analysis ===
+
Since EM.Illumina is a surface simulator, only the exterior surface of solid CAD objects is discretized, as the interior volume is not taken into account in a PO analysis. By contrast, surface CAD objects are assumed to be double-sided. In other words, the default PO mesh of a surface object consists of coinciding double cells, one representing the upper or positive side and the other representing the lower or negative side. This may lead to a very large number of cells. EM.Illumina's mesh generator has settings that allow you to treat all mesh cells as double-sided or all single-sided. You can do that in the Mesh Settings dialog by checking the boxes labeled '''All Double-Sided Cells''' and '''All Single-Sided Cells'''. This is useful when your project workspace contains well-organized and well-oriented surface CAD objects only. In the single-sided case, it is very important that all the normals to the cells point towards the source. Otherwise, your surfaces  fall in the shadow region, and no currents will be computed on them. By checking the box labeled '''Reverse Normal''', you instruct EM.Illumina to reverse the direction of the normal vectors globally at the surface of all the cells.
  
−
To open [[PO Module]]'s Simulation Run dialog, click the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu &gt; Simulate &gt; Run...'''or use the keyboard shortcut '''Ctrl+R'''. To start the simulation click the '''Run''' button of this dialog. Once the PO simulation starts, a new dialog called '''Output Window''' opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, [[EM.Cube]] generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.
+
[[Image:Info_icon.png|30px]] Click here to learn more about '''[[Preparing_Physical_Structures_for_Electromagnetic_Simulation#Working_with_EM.Cube.27s_Mesh_Generators | Working with Mesh Generator]]'''.
  
−
[[File:PO27.png]]
+
[[Image:Info_icon.png|30px]] Click here to learn more about '''[[Preparing_Physical_Structures_for_Electromagnetic_Simulation#The_Triangular_Surface_Mesh_Generator | EM.Illumina's Triangular Surface Mesh Generator ]]'''.
  
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Figure 1: [[PO Module]]'s Simulation Run dialog.
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<table>
 +
<tr>
 +
<td> [[Image:POShip1.png|thumb|600px|Geometry of a metallic battleship model with a short horizontal dipole radiator above it.]] </td>
 +
</tr>
 +
<tr>
 +
<td> [[Image:POShip2.png|thumb|600px|Trinagular surface mesh of the metallic battleship model.]] </td>
 +
</tr>
 +
</table>
  
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=== Setting The Numerical Parameters ===
+
== Running PO Simulations in EM.Illumina ==
  
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Before you run a PO simulation, you can change some of the PO simulation engine settings. While in the [[PO Module]]'s '''Simulation Run Dialog''', click the '''Settings''' button next to the '''Select Engine''' dropdown list. In the Physical Optics Engine Settings Dialog, there are two options for '''Solver Type''': '''Iterative''' and '''GOPO'''. The default option is Iterative. The GOPO solver is a zero-order PO simulator that uses Geometrical Optics (GO) to determine the lit and shadow cells in the structure's mesh. For the termination of the IPO solver, there are two options: '''Convergence Error''' and '''Maximum Number of Iterations'''. The default Termination Criterion is based on convergence error, which has a default value of 0.1 and can be changed to any desired accuracy. The convergence error is defined as the L2 norm of the normalized residual error in the combined '''J/M''' current solution of the entire discretized structure from one iteration to the next. Note that for this purpose, the magnetic currents are scaled by &eta;<sub>0</sub> in the residual error vector.
+
=== EM.Illumina's Simulation Modes ===
  
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You can also use higher- or lower-order integration schemes for the calculation of field integrals. [[EM.Cube]]'s PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: '''7-Point Quadrature''', '''3-Point Quadrature''' and '''Constant'''. For integration of rectangular cells, too, you have three options: '''9-Point Quadrature''', '''4-Point Quadrature''' and '''Constant'''.
+
Once you have set up your structure in [[EM.Illumina]], have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. [[EM.Illumina]] offers five simulation modes:
  
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[[File:PO28.png]]
+
{| class="wikitable"
 +
|-
 +
! scope="col"| Simulation Mode
 +
! scope="col"| Usage
 +
! scope="col"| Number of Engine Runs
 +
! scope="col"| Frequency
 +
! scope="col"| Restrictions
 +
|-
 +
| style="width:120px;" | [[#Running A Single-Frequency PO Analysis | Single-Frequency Analysis]]
 +
| style="width:270px;" | Simulates the physical structure "As Is"
 +
| style="width:80px;" | Single run
 +
| style="width:250px;" | Runs at the center frequency fc
 +
| style="width:80px;" | None
 +
|-
 +
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Frequency_Sweep_Simulations_in_EM.Cube | Frequency Sweep]]
 +
| style="width:270px;" | Varies the operating frequency of the PO solver 
 +
| style="width:80px;" | Multiple runs
 +
| style="width:250px;" | Runs at a specified set of frequency samples
 +
| style="width:80px;" | None
 +
|-
 +
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Running_Parametric_Sweep_Simulations_in_EM.Cube | Parametric Sweep]]
 +
| style="width:270px;" | Varies the value(s) of one or more project variables
 +
| style="width:80px;" | Multiple runs
 +
| style="width:250px;" | Runs at the center frequency fc
 +
| style="width:80px;" | None
 +
|-
 +
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Performing_Optimization_in_EM.Cube | Optimization]]
 +
| style="width:270px;" | Optimizes the value(s) of one or more project variables to achieve a design goal
 +
| style="width:80px;" | Multiple runs
 +
| style="width:250px;" | Runs at the center frequency fc
 +
| style="width:80px;" | None
 +
|-
 +
| style="width:120px;" | [[Parametric_Modeling_%26_Simulation_Modes_in_EM.Cube#Generating_Surrogate_Models | HDMR Sweep]]
 +
| style="width:270px;" | Varies the value(s) of one or more project variables to generate a compact model
 +
| style="width:80px;" | Multiple runs
 +
| style="width:250px;" | Runs at the center frequency fc
 +
| style="width:80px;" | None
 +
|}
  
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Figure 1: [[PO Module]]'s Simulation Engine Settings dialog.
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You can set the simulation mode from [[EM.Illumina]]'s "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain parameters are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.
  
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=== PO Sweep Simulations ===
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=== Running A Single-Frequency PO Analysis ===
  
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You can run [[EM.Cube]]'s PO simulation engine in the sweep mode, whereby a parameter like frequency, plane wave incident angles or a user defined variable is varied over a specified range at predetermined samples. The output data are saved into data files for visualization and plotting. [[EM.Cube]]'s [[PO Module]] currently offers three types of sweep:
+
To open [[EM.Illumina]]'s Simulation Run dialog, click the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu &gt; Simulate &gt; Run...'''or use the keyboard shortcut {{key|Ctrl+R}}. To start the simulation click the {{key|Run}} button of this dialog. Once the PO simulation starts, a new dialog called '''Output Window''' opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, [[EM.Cube]] generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.
  
−
# Frequency Sweep
+
<table>
−
# Angular Sweep
+
<tr>
−
# Parametric Sweep
+
<td> [[Image:Illumina L1 Fig10A.png|thumb|left|480px|EM.Illumina's Simulation Run dialog.]] </td>
 +
</tr>
 +
</table>
  
−
To run a PO sweep, open the '''Simulation ''''''Run Dialog''' and select one of the above sweep types from the '''Simulation Mode''' dropdown list of this dialog. If you select either frequency or angular sweep, the '''Settings''' button located next to the simulation mode dropdown list becomes enabled. If you click this button, the Frequency Settings Dialog or Angle Settings Dialog opens up, respectively. In the frequency settings dialog, you can set the start and end frequencies as well as the number of frequency samples. The start and end frequency values are initially set based on the project's center frequency and bandwidth. During a frequency sweep, as the project's frequency changes, so does the wavelength. As a result, the mesh of the structure also changes at each frequency sample. The frequency settings dialog gives you three choices regarding the mesh of the project structure during a frequency sweep:
+
=== Setting The Numerical Parameters ===
  
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# Fix mesh at the highest frequency.
+
Before you run a PO simulation, you can change some of the PO simulation engine settings. While in the [[EM.Illumina]]'s '''Simulation Run Dialog''', click the '''Settings''' button next to the '''Select Engine''' dropdown list. In the Physical Optics Engine Settings Dialog, there are two options for '''Solver Type''': '''Iterative''' and '''GOPO'''. The default option is Iterative. The GOPO solver is a zero-order PO simulator that uses Geometrical Optics (GO) to determine the lit and shadow cells in the structure's mesh. For the termination of the IPO solver, there are two options: '''Convergence Error''' and '''Maximum Number of Iterations'''. The default Termination Criterion is based on convergence error, which has a default value of 0.1 and can be changed to any desired accuracy. The convergence error is defined as the L2 norm of the normalized residual error in the combined '''J/M''' current solution of the entire discretized structure from one iteration to the next. Note that for this purpose, the magnetic currents are scaled by &eta;<sub>0</sub> in the residual error vector.
−
# Fix mesh at the center frequency.
+
−
# Re-mesh at each frequency.
+
  
−
You can run an angular sweep only if your project has a plane wave excitation. In this case, you have to define a plane wave source with the default settings. During an angular sweep, either the incident theta angle or incident phi angle is varied within the specified range. The other angle remains fixed at the value that is specified in the '''Plane Wave Dialog'''. You have to select either '''Theta''' or '''Phi''' as the '''Sweep Angle''' in the Angle Settings Dialog. You also need to set the start and end angles as well as the number of angle samples.
+
You can also use higher- or lower-order integration schemes for the calculation of field integrals. [[EM.Cube]]'s PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: '''7-Point Quadrature''', '''3-Point Quadrature''' and '''Constant'''. For integration of rectangular cells, too, you have three options: '''9-Point Quadrature''', '''4-Point Quadrature''' and '''Constant'''.
−
 
+
−
In a parametric sweep, one or more user defined [[variables]] are varied at the same time over their specified ranges. This creates a parametric space with the total number of samples equal to the product of the number of samples for each variable. The user defined [[variables]] are defined using [[EM.Cube]]'s '''[[Variables]] Dialog'''. For a description of [[EM.Cube]] [[variables]], please refer to the &quot;Parametric Modeling, Sweep &amp; [[Optimization]]&quot; section of [[EM.Cube]] Manual or see the &quot;Parametric Sweep&quot; sections of the FDTD or [[Planar Module]] manuals.
+
−
 
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[[File:po_phys52.png]] [[File:po_phys54.png]]
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Figure 1: [[PO Module]]'s Frequency Settings and Angle Settings dialogs.
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== Working with PO Simualtion Data ==
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[[File:PO28.png|thumb|left|480px|EM.Illumina's Simulation Engine Settings dialog.]]
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=== Visualizing Current Distributions ===
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[[File:PO37.png|thumb|300px|PO Module's Current Distribution dialog]]
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At the end of a PO simulation, [[EM.Cube]]'s PO engine generates a number of output data files that contain all the computed simulation data. The main output data are the electric and magnetic current distributions. You can easily examine the 3D color-coded intensity plots of current distributions in the project workspace. Current distributions are visualized on the surface of the PO mesh cells, and the magnitude and phase of the electric and magnetic surface currents are plotted for all the objects. In order to view these currents, you must first define a current distribution observable before running the PO simulation. To do this, right click on the '''Current Distributions''' item in the '''Observables''' section of the Navigation Tree and select '''Insert New Observable...'''. The Current Distribution Dialog opens up. Accept the default settings and close the dialog. A new current distribution node is added to the Navigation Tree. Unlike the [[Planar Module]], in the [[PO Module]] you can define only one current distribution node in the Navigation Tree, which covers all the objects in the project workspace. After a PO simulation is completed, new plots are added under the current distribution node of the Navigation Tree. Separate plots are produced for the magnitude and phase of each of the electric and magnetic surface current components (X, Y and Z) as well as the total current magnitude. The magnitude maps are plotted on a normalized scale with the minimum and maximum values displayed in the legend box. The phase maps are plotted in radians between -p and p. Note that sometimes the current distribution plots may hide inside smooth and curved objects, and you cannot see them. You may have to freeze such objects or switch to the mesh view mode.
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[[File:PO38.png|800px]]
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Figure: The current distribution plot of a PEC sphere illuminated by an obliquely incident plane wave.
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[[File:PO42(4).png|thumb|300px|PO Module's Field Sensor dialog]]
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[[EM.Cube]] allows you to visualize the near fields at a specific field sensor plane. Calculation of near fields is a post-processing process and may take a considerable amount of time depending on the resolution that you specify. To define a new Field Sensor, follow these steps:
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* Right click on the '''Field Sensors''' item in the '''Observables''' section of the Navigation Tree and select '''Insert New Observable...'''
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* The '''Label''' box allows you to change the sensor’s name. you can also change the color of the field sensor plane using the '''Color''' button.
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* By default [[EM.Cube]] creates a field sensor plane passing through the origin of coordinates (0,0,0) on the XY plane. You can change the location of the sensor plane to any point by typing in new values for the X, Y and Z '''Center Coordinates'''. You can also change these coordinates using the spin buttons.
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* The initial size of the sensor plane is 100 × 100 project units. You can change the dimensions of the sensor plane to any desired size. You can also set the '''Number of Samples''' along the different directions. These numbers determine the resolution of near field maps. Keep in mind that large numbers of samples may result in long computation times.
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After closing the Field Sensor Dialog, a new field sensor item immediately appears under the '''Observables''' section in the Navigation Tree. Once a PO simulation is finished, a total of 14 plots are added to every field sensor node in the Navigation Tree. These include the magnitude and phase of all three components of '''E''' and '''H''' fields and the total electric and magnetic field values. Click on any of these items and a color-coded intensity plot of it will be visualized on the project workspace. A legend box appears in the upper right corner of the field plot, which can be dragged around using the left mouse button. The values of the magnitude plots are normalized between 0 and 1. The legend box contains the minimum field value corresponding to 0 of the color map, maximum field value corresponding to 1 of the color map, and the unit of the field quantity, which is V/m for E-field and A/m for H-field. The values of phase plots are always shown in Radians between -p and p.To display the fields properly, the structure is cut through the field sensor plane, and only part of it is shown. If the structure still blocks your view, you can simply hide or freeze it. You can change the view of the field plot with the available view operations such as rotate view, pan, zoom, etc.
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{{Note|Keep in mind that since Physical Optics is an asymptotic method, the field sensors must be placed at adequate distances (at least one or few wavelengths) away from the scatterers to produce acceptable results.}}
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[[File:PO43.png|400px]] [[File:PO44.png|400px]]
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Figure 2: Near field plots of electric and magnetic fields on a sensor plane.
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[[File:PO45.png|thumb|300px|PO Module's Radiation Pattern dialog]]
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Unlike the FDTD method, Physical Optics is an open-boundary technique. You do not need a far field box to perform near-to-far-field transformations. Nonetheless, you still need to define a far field observable if you want to plot radiation patterns. A far field can be defined by right clicking on the '''Far Fields''' item in the '''Observables''' section of the Navigation Tree and selecting '''Insert New Radiation Pattern...''' from the contextual menu. The Radiation Pattern dialog opens up. You can accept most of the default settings in this dialog. The Output Settings section allows you to change the '''Angle Increment''' in the degrees, which sets the resolution of far field calculations. The default value is 5 degrees. After closing the radiation pattern dialog, a far field entry immediately appears with its given name under the '''Far Fields''' item of the Navigation Tree.
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After a PO simulation is finished, three radiation patterns plots are added to the far field node in the Navigation Tree. These are the far field component in &theta; direction, the far field component in &phi; direction and the total far field defines as:
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:<math>|\mathbf{E_{ff,tot}}| = \sqrt{ |E_{\theta}|^2 + |E_{\phi}|^2 }</math>
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<!--[[File:FDTD129.png]]-->
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The 3D plots can be viewed by clicking on their name in the navigation tree. They are displayed in [[EM.Cube]]'s project workspace and are overlaid on the project's structure. The view of a 3D radiation pattern plots can be changed with the available view operations such as rotate view, pan, zoom, etc. If the structure blocks the view of the pattern, you can simply hide the whole structure or parts of it. The fields are always normalized to the maximum of the total far field. A legend box appears in the upper right corner of the 3D radiation plot, which can be moved around by clicking and dragging with the left mouse button. The calculated Directivity of the radiating structure is displayed at the bottom of the legend box. It is important to note that if the PO structure is excited by an incident plane wave, the radiation patterns indeed represent the far-zone scattered field data.
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[[File:PO46.png|800px]]
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Figure: 3D radiation pattern of a parabolic dish reflector excited by a short dipole at its focal point.
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[[File:PO47.png|thumb|300px|PO Module's RCS dialog]]
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When the physical structure is excited by a plane wave source, the calculated far field data indeed represent the scattered fields. [[EM.Cube]] calculates the radar cross section (RCS) of a target, which is defined in the following manner:
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:<math> \sigma_{\theta} = 4\pi r^2 \dfrac{ \big| \mathbf{E}_{\theta}^{scat} \big| ^2} {\big| \mathbf{E}^{inc} \big|^2}, \quad \sigma_{\phi} = 4\pi r^2 \dfrac{ \big| \mathbf{E}_{\phi}^{scat} \big| ^2} {\big| \mathbf{E}^{inc} \big|^2}, \quad \sigma = \sigma_{\theta} + \sigma_{\phi} = 4\pi r^2 \dfrac{ \big| \mathbf{E}_{tot}^{scat} \big| ^2} {\big| \mathbf{E}^{inc} \big|^2} </math>
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<!--[[File:FDTD130.png]]-->
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Three RCS quantities are computed: the &theta; and &phi; components of the radar cross section as well as the total radar cross section, which are dented by &sigma;<sub>&theta;</sub>, &sigma;<sub>&phi;</sub>, and &sigma;<sub>tot</sub>. In addition, [[EM.Cube]]'s [[PO Module]] 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 &theta;<sub>0</sub> and &phi;<sub>0</sub>, and the RCS is measured and plotted at all &theta; and &phi; angles. In mono-static RCS, the structure is illuminated by a plane wave at incidence angles &theta;<sub>0</sub> and &phi;<sub>0</sub>, and the RCS is measured and plotted at the echo angles 180°-&theta;<sub>0</sub>; and &phi;<sub>0</sub>. It is clear that in the case of mono-static RCS, the PO simulation engine runs an internal angular sweep, whereby the values of the plane wave incidence angles &theta; and &phi; are varied over the entire intervals [0°, 180°] and [0°, 360°], respectively, and the backscatter RCS is recorded.
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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 &theta; and &phi; angles are incremented by 5 degrees. At the end of a PO simulation, besides calculating the RCS data over the entire (spherical) 3D space, a number of 2D 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 f-cut. This latter cut is at f = 45° by default. You can assign another azimuth angle in degrees in the box labeled '''Non-Principal Phi Plane'''.
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At the end of a PO simulation, the thee RCS plots &sigma;<sub>&theta;</sub>, &sigma;<sub>&phi;</sub>, and &sigma;<sub>tot</sub> are added under the far field section of the Navigation Tree. These plots are very similar to the three 3D 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 3D plots are normalized to the maximum RCS value, which is also displayed in the legend box. Keep in mind that computing the 3D mono-static RCS may take an enormous amount of computation time.
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Figure: RCS of a PEC sphere illuminated by an laterally incident plane wave.
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[[Image:Tutorial_icon.png|30px]] '''[[EM.Cube#EM.Illumina_Documentation | EM.Illumina Tutorial Gateway]]'''
  
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[[EM.Cube | Back to EM.Cube Main Page]]
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Latest revision as of 00:43, 3 May 2021

Splash-po.jpg

Fast Asymptotic Solver For Large-Scale Scattering Problems

Cube-icon.png Cad-ico.png Fdtd-ico.png Prop-ico.png Static-ico.png Planar-ico.png Metal-ico.png

Tutorial icon.png EM.Illumina Tutorial Gateway

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Product Overview

EM.Illumina in a Nutshell

EM.Illumina is a 3D electromagnetic simulator for modeling large free-space structures. It features a high frequency asymptotic solver based on Physical Optics (PO) for simulation of electromagnetic scattering from large metallic structures and impedance surfaces. You can use EM.Illumina to compute the radar cross section (RCS) of large target structures like aircraft or vehicles or simulate the radiation of antennas in the presence of large platforms.

EM.Illumina provides a computationally efficient alternative for extremely large structures when a full-wave solution becomes prohibitively expensive. Based on a high frequency asymptotic physical optics formulation, it assumes that an incident source generates currents on a metallic structure, which in turn reradiate into the free space. A challenging step in establishing the PO currents is the determination of the lit and shadowed points on complex scatterer geometries. Ray tracing from each source to the points on the scatterers to determine whether they are lit or shadowed is a time consuming task. To avoid this difficulty, EM.Illumina's simulator uses a novel Iterative Physical Optics (IPO) formulation, which automatically accounts for multiple shadowing effects.The IPO technique can effectively capture dominant, near-field, multiple scattering effects from electrically large targets.

Info icon.png Click here to lean more about the Theory of Physical Optics.

Analyzing scattering from a trihedral corner reflector using IPO solver.

EM.Illumina as the Physical Optics Module of EM.Cube

EM.Illumina is the high-frequency, asymptotic Physical Optics Module of EM.Cube, a comprehensive, integrated, modular electromagnetic modeling environment. EM.Illumina shares the visual interface, 3D parametric CAD modeler, data visualization tools, and many more utilities and features collectively known as CubeCAD with all of EM.Cube's other computational modules.

EM.Illumina's simulator is seamlessly interfaced with EM.CUBE's other simulattion engines. This module is the ideal place to define Huygens sources. These are based on Huygens surface data that are generated using a full-wave simulator like EM.Tempo, EM.Picasso or EM.Libera.

Info icon.png Click here to learn more about EM.Cube Modeling Environment.

Advantages & Limitations of EM.Illumina's PO Solver

EM.Illumina provides a computationally efficient alternative to full-wave solutions for extremely large structures when full-wave analysis becomes prohibitively expensive. For simple scatterer geometries, EM.Illumina's GO-PO solver is fairly adequate. But for complex geometries that involve multiple shadowing effects, the IPO solver must be utilized. The IPO technique can effectively capture dominant, near-field, multiple scattering effects from electrically large targets with concave surfaces. You have to remember that Physical Optics is a surface simulator. This is not a problem for PEC and PMC objects, which have zero internal fields, or even impedance surfaces, where you can satisfy the boundary conditions on one side of a surface only. PO analysis cannot handle the fields inside dielectric objects. Additionally, most coupling effects between adjacent scatterers are ignored.

Computed radiation pattern of a short dipole radiator over a large metallic battleship.

EM.Illumina Features at a Glance

Structure Definition

  • Metal (PEC) solids and surfaces in free space
  • PMC and impedance surfaces in free space
  • Import STL CAD files as native polymesh structures
  • Huygens blocks imported from full-wave modules

Sources

  • Short dipoles
  • Import previously generated wire mesh solution as collection of short dipoles
  • Plane wave excitation with linear and circular polarizations
  • Multi-ray excitation capability (ray data imported from EM.Terrano or external files)
  • Huygens sources imported from PO or other modules with arbitrary rotation and array configuration

Mesh Generation

  • Surface triangular mesh with control over tessellation parameters
  • Local mesh editing of polymesh objects

Physical Optics Simulation

  • Physical Optics solution of metal scatterers and impedance surfaces
  • Conventional Geometrical Optics - Physical Optics (GOPO) solver
  • Novel iterative PO solver for fast simulation of multiple shadowing effects and multi-bounce reflections
  • Calculation of near fields, far fields and scattering cross section (bistatic and monostatic RCS)
  • Frequency and angular sweeps with data animation
  • Parametric sweep with variable object properties or source parameters
  • Multi-variable and multi-goal optimization of structure
  • Remote simulation capability
  • Both Windows and Linux versions of PO simulation engine available

Data Generation & Visualization

  • Electric and magnetic surface current distributions on metallic or impedance surfaces
  • Near field intensity plots (vectorial - amplitude & phase)
  • Huygens surface data generation for use in PO or other EM.Cube modules
  • Far field radiation patterns: 3D pattern visualization and 2-D Cartesian and polar graphs
  • Bi-static and monostatic radar cross section: 3D visualization and 2D graphs
  • Custom output parameters defined as mathematical expressions of standard outputs

Building the Physical Structure in EM.Illumina

The Variety of Surface Types in EM.Illumina

EM.Illumina organizes physical objects by their surface type. Any object in EM.Illumina is assumed to be made of one of the three surface types:

Icon Material Type Applications Geometric Object Types Allowed
Pec group icon.png Perfect Electric Conductor (PEC) Surface Modeling perfect metal surfaces Solid and surface objects
Pmc group icon.png Perfect Magnetic Conductor (PMC) Surface Modeling perfect magnetic surfaces Solid and surface objects
Voxel group icon.png Impedance/Dielectric Surface Modeling impedance surfaces as an equivalent to the surface of dielectric objects Solid and surface objects
Virt group icon.png Virtual Object Used for representing non-physical items All types of objects

Click on each category to learn more details about it in the Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types.

EM.Illumina can only handle surface and solid CAD objects. Only the outer surface of solid objects is considered in the PO simulation. No line or curve objects are allowed in the project workspace; or else, they will be ignored during the PO simulation.

Organizing Geometric Objects by Surface Type

You can define several PEC, PMC or impedance surface groups with different colors and impedance values. All the objects created and drawn under a group share the same color and other properties. Once a new surface node has been created on the navigation tree, it becomes the "Active" surface group of the project workspace, which is always listed in bold letters. When you draw a new CAD object such as a Box or a Sphere, it is inserted under the currently active surface type. There is only one surface group that is active at any time. Any surface type can be made active by right clicking on its name in the navigation tree and selecting the Activate item of the contextual menu. It is recommended that you first create surface groups, and then draw new objects under the active surface group. However, if you start a new EM.Illumina project from scratch, and start drawing a new object without having previously defined any surface groups, a new default PEC surface group is created and added to the navigation tree to hold your new CAD object.

Info icon.png Click here to learn more about Moving Objects among Different Groups.

Attention icon.png In EM.Cube, you can import external CAD models (such as STEP, IGES, STL models, etc.) only to CubeCAD. From CubeCAD, you can then move the imported objects to EM.Illumina.
EM.Illumina's navigation tree.

EM.Illumina's Excitation Sources

EM.Illumina provides three types of sources for the excitation of your physical optics simulation:

Icon Source Type Applications Restrictions
Hertz src icon.png Hertzian Short Dipole Source Almost omni-directional physical radiator None, stand-alone source
Plane wave icon.png Plane Wave Source Used for modeling scattering None, stand-alone source
Huyg src icon.png Huygens Source Used for modeling equivalent sources imported from other EM.Cube modules Imported from a Huygens surface data file

Click on each category to learn more details about it in the Glossary of EM.Cube's Materials, Sources, Devices & Other Physical Object Types.

A short Hertzian dipole is the simplest way of exciting a structure in EM.Illumina. A short dipole source acts like an infinitesimally small ideal current source. The total radiated power by your dipole source is calculated and displayed in Watts in its property dialog. Your physical structure in EM.Illumina can also be excited by an incident plane wave. In particular, you need a plane wave source to compute the radar cross section of a target. The direction of incidence is defined by the θ and φ angles of the unit propagation vector in the spherical coordinate system. The default values of the incidence angles are θ = 180° and φ = 0° corresponding to a normally incident plane wave propagating along the -Z direction with a +X-polarized E-vector. Huygens sources are virtual equivalent sources that capture the radiated electric and magnetic fields from another structure that was previously analyzed in another EM.Cube computational module.

EM.Illumina's Simulation Data & Observables

EM.Illumina does not produce any output data on its own unless you define one or more observables for your simulation project. The primary output data in the Physical Optics method are the electric and magnetic surface current distributions on the surface of your structure. At the end of a PO simulation, EM.Illumina generates a number of output data files that contain all the computed simulation data. Once the current distributions are known, EM.Illumina can compute near-field distributions as well as far-field quantities such as radiation patterns and radar cross section (RCS).

EM.Illumina currently provides the following observables:

Icon Simulation Data Type Observable Type Applications Restrictions
Currdistr icon.png Current Distribution Maps Current Distribution Computing electric surface current distribution on PEC and impedance surfaces and magnetic surface current distribution on PMC and impedance surfaces None
Fieldsensor icon.png Near-Field Distribution Maps Near-Field Sensor Computing electric and magnetic field components on a specified plane in the frequency domain None
Farfield icon.png Far-Field Radiation Characteristics Far-Field Radiation Pattern Computing the radiation pattern and additional radiation characteristics such as directivity, axial ratio, side lobe levels, etc. None
Rcs icon.png Far-Field Scattering Characteristics Radar Cross Section (RCS) Computing the bistatic and monostatic RCS of a target Requires a plane wave source
Huyg surf icon.png Equivalent electric and magnetic surface current data Huygens Surface Collecting tangential field data on a box to be used later as a Huygens source in other EM.Cube modules None

Click on each category to learn more details about it in the Glossary of EM.Cube's Simulation Observables & Graph Types.

Current distributions are visualized on the surface of PO mesh cells, and the magnitude and phase of the electric and magnetic surface currents are plotted for all the objects. A single current distribution node in the navigation tree holds the current distribution data for all the objects in the project workspace. Since the currents are plotted on the surface of the individual mesh cells, some parts of the plots may be blocked by and hidden inside smooth and curved objects. To be able to view those parts, you may have to freeze the obstructing objects or switch to the mesh view mode.

The current distribution plot of a PEC sphere illuminated by an obliquely incident plane wave.

EM.Illumina allows you to visualize the near fields at a predefined field sensor plane of arbitrary dimensions. Calculation of near fields is a post-processing process and may take a considerable amount of time depending on the resolution that you specify.

Attention icon.png Keep in mind that since Physical Optics is an asymptotic method, the field sensors must be placed at adequate distances (at least one or few wavelengths) away from the scatterers to produce acceptable results.
Electric field distribution on a sensor plane above a metallic sphere.
Magnetic field distribution on a sensor plane above a metallic sphere.

You need to define a far field observable if you want to plot the radiation patterns of your physical structure. After a PO simulation is finished, three 3D radiation patterns plots are displayed in the project workspace and are overlaid on your physical structure. These are the Theta and Phi components of the far-zone electric fields as well as the total far field.

Attention icon.png The 3D radiation pattern is always displayed at the origin of the spherical coordinate system, (0,0,0), with respect to which the far radiation zone is defined. Oftentimes, this might not be the radiation center of your physical structure.
3D radiation pattern of a parabolic dish reflector excited by a short dipole at its focal point.

When your physical structure is excited by a plane wave source, the calculated far field data indeed represent the scattered fields. EM.Illumina can calculate 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 θ0 and φ0, 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 θ0 and φ0, and the RCS is measured and plotted at the echo angles 180°-θ0; and φ0. It is clear that in the case of mono-static RCS, the PO simulation engine runs an internal angular sweep, whereby the values of the plane wave incidence angles θ and φ are varied over the entire 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. At the end of a PO simulation, the thee RCS plots σθ, σφ, and σtot are added under the far field section of the navigation tree. Keep in mind that computing the 3D mono-static RCS may take an enormous amount of computation time.

Attention icon.png The 3D RCS plot is always displayed at the origin of the spherical coordinate system, (0,0,0), with respect to which the far radiation zone is defined. Oftentimes, this might not be the scattering center of your physical structure.
RCS of a PEC sphere illuminated by an laterally incident plane wave.

Discretizing the Physical Structure in EM.Illumina

EM.Illumina uses a triangular surface mesh to discretize the structure of your project workspace. The mesh generating algorithm tries to generate regularized triangular cells with almost equal surface areas across the entire structure. You can control the cell size using the "Mesh Density" parameter. By default, the mesh density is expressed in terms of the free-space wavelength. The default mesh density is 10 cells per wavelength. In the Physical Optics method, the electric and magnetic surface currents, J and M, are assumed to be constant on the surface of each triangular cell. On flat surfaces, the unit normal vectors to all the cells are identical. Incident plane waves or other relatively uniform source fields induce uniform PO currents on all these cells. Therefore, a high resolution mesh may not be necessary on flat surface or faces. Accurate discretization of curved objects like spheres or ellipsoids, however, requires a high mesh density.

EM.Illumina's Mesh Settings dialog.

Since EM.Illumina is a surface simulator, only the exterior surface of solid CAD objects is discretized, as the interior volume is not taken into account in a PO analysis. By contrast, surface CAD objects are assumed to be double-sided. In other words, the default PO mesh of a surface object consists of coinciding double cells, one representing the upper or positive side and the other representing the lower or negative side. This may lead to a very large number of cells. EM.Illumina's mesh generator has settings that allow you to treat all mesh cells as double-sided or all single-sided. You can do that in the Mesh Settings dialog by checking the boxes labeled All Double-Sided Cells and All Single-Sided Cells. This is useful when your project workspace contains well-organized and well-oriented surface CAD objects only. In the single-sided case, it is very important that all the normals to the cells point towards the source. Otherwise, your surfaces fall in the shadow region, and no currents will be computed on them. By checking the box labeled Reverse Normal, you instruct EM.Illumina to reverse the direction of the normal vectors globally at the surface of all the cells.

Info icon.png Click here to learn more about Working with Mesh Generator.

Info icon.png Click here to learn more about EM.Illumina's Triangular Surface Mesh Generator .

Geometry of a metallic battleship model with a short horizontal dipole radiator above it.
Trinagular surface mesh of the metallic battleship model.

Running PO Simulations in EM.Illumina

EM.Illumina's Simulation Modes

Once you have set up your structure in EM.Illumina, have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. EM.Illumina offers five simulation modes:

Simulation Mode Usage Number of Engine Runs Frequency Restrictions
Single-Frequency Analysis Simulates the physical structure "As Is" Single run Runs at the center frequency fc None
Frequency Sweep Varies the operating frequency of the PO solver Multiple runs Runs at a specified set of frequency samples None
Parametric Sweep Varies the value(s) of one or more project variables Multiple runs Runs at the center frequency fc None
Optimization Optimizes the value(s) of one or more project variables to achieve a design goal Multiple runs Runs at the center frequency fc None
HDMR Sweep Varies the value(s) of one or more project variables to generate a compact model Multiple runs Runs at the center frequency fc None

You can set the simulation mode from EM.Illumina's "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain parameters are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.

Running A Single-Frequency PO Analysis

To open EM.Illumina's Simulation Run dialog, click the Run Run icon.png button of the Simulate Toolbar or select Menu > Simulate > Run...or use the keyboard shortcut Ctrl+R. To start the simulation click the Run button of this dialog. Once the PO simulation starts, a new dialog called Output Window opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, EM.Cube generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.

EM.Illumina's Simulation Run dialog.

Setting The Numerical Parameters

Before you run a PO simulation, you can change some of the PO simulation engine settings. While in the EM.Illumina's Simulation Run Dialog, click the Settings button next to the Select Engine dropdown list. In the Physical Optics Engine Settings Dialog, there are two options for Solver Type: Iterative and GOPO. The default option is Iterative. The GOPO solver is a zero-order PO simulator that uses Geometrical Optics (GO) to determine the lit and shadow cells in the structure's mesh. For the termination of the IPO solver, there are two options: Convergence Error and Maximum Number of Iterations. The default Termination Criterion is based on convergence error, which has a default value of 0.1 and can be changed to any desired accuracy. The convergence error is defined as the L2 norm of the normalized residual error in the combined J/M current solution of the entire discretized structure from one iteration to the next. Note that for this purpose, the magnetic currents are scaled by η0 in the residual error vector.

You can also use higher- or lower-order integration schemes for the calculation of field integrals. EM.Cube's PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: 7-Point Quadrature, 3-Point Quadrature and Constant. For integration of rectangular cells, too, you have three options: 9-Point Quadrature, 4-Point Quadrature and Constant.

EM.Illumina's Simulation Engine Settings dialog.


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