== Using EM.Terrano as an Asymptotic Field Solver ==
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=== Defining Sources & Observables for Your SBR Simulation ===
Like every other electromagnetic solver, EM.Terrano's SBR ray tracer requires an excitation source and one or more observables for the generation of simulation data. EM.Terrano offers several types of sources and observables for a SBR simulation. You already learned about the transmitter set as a source and the receiver set as an observable. You can mix and match different source types and observable types depending on the requirements of your modeling problem.
Click on each type to learn more about it in the [[Glossary of EM.Cube's Simulation Observables]].
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A short dipole source is the simplest type of excitation for your propagation scene. A short dipole has an almost "omni-directional" radiation pattern, and is the closest thing to an isotropic radiator. EM.Terrano does not provide a theoretical/hypothetical isotropic transmitter because its SBR solver is fully polarimetric and requires a real physical radiator for ray generation. A transmitter is a more sophisticated source that requires a base point as well as an imported radiation pattern file with a '''.RAD''' file extension.
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Of the above list of EM.Terrano's observables types, receivers are the ones you would typically use for your propagation scenes. Unlike a transmitter, a receiver by default does not require an imported radiation pattern file. A default receiver is assumed to be polarization-matched to the incoming ray. The other three observable types, field sensor, far fields and Huygens surface are primarily used in applications that utilize EM.Terrano as an asymptotic electromagnetic field solver. The Huygens surface observable is primarily used for [[Hybrid Modeling using Multiple Simulation Engines|hybrid modeling using multiple simulation engines]].
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{{Note| In order to define either transmitters or receivers, first you have to define base points. For a transmitter, you additionally need to import a radiation pattern file from one of [[EM.Cube]]'s other computational modules.}}
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[[File:PROP18(1).png|thumb|350px|EM.Terrano's Short Dipole Source dialog.]]
The simplest SBR simulation can be performed using a short dipole source with a specified field sensor plane. As an asymptotic EM solver, EM.Terrano then computes the electric and magnetic fields radiated by your dipole source in the presence of your multipath propagation environment. EM.Terrano's short dipole source and field sensor observable are very similar to those of [[EM.Cube]]'s other computational modules. You can also compute the far field radiation patterns of a dipole in the presence of surrounding scatterers or compute the Huygens surface data for use in [[EM.Cube]]'s other modules.
<!--[[Image:Info_icon.png|40px]] Click here to learn more about using EM.Terrano as an '''[[Asymptotic Field Solver]]'''.-->
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=== Defining a Hertzian Dipole Source ===
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A short dipole is the simplest way of exciting a structure in [[EM.Terrano]]. It is also the closest thing to an omnidirectional radiator. The direction or orientation of the short dipole determines its polarization. Note that EM.Terrano does not offer an isotropic radiator as a source type because it is a polarimetric ray tracer. A short dipole source acts like an infinitesimally small ideal current source. A short dipole source appears as a small arrow in your scene. The total radiated power by your dipole source is calculated and displayed in Watts in its property dialog.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Hertzian_Dipole_Sources | Hertzian Dipole Sources]]'''.
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=== Defining a Field Sensor ===
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[[File:PROP18(2).png|thumb|350px|EM.Terrano's Field Sensor dialog]]
As an asymptotic electromagnetic field solver, the SBR simulation engine can compute the electric and magnetic field distributions in a specified plane. In order to view these field distributions, you must first define field sensor observables before running the SBR simulation. To do that, right click on the '''Field Sensors''' item in the '''Observables''' section of the navigation tree and select '''Insert New Observable...'''. The Field Sensor Dialog opens up. At the top of the dialog and in the section titled '''Sensor Plane Location''', first you need to set the plane of field calculation. In the dropdown box labeled '''Direction''', you have three options X, Y, and Z, representing the"normals" to the XY, YZ and ZX planes, respectively. The default direction is Z, i.e. XY plane parallel to the substrate layers. In the three boxes labeled '''Coordinates''', you set the coordinates of the center of the plane. Then, you specify the '''Size''' of the plane in project units, and finally set the '''Number of Samples''' along the two sides of the sensor plane. The larger the number of samples, the smoother the near field map will appear.
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Once you close the Field Sensor dialog, its name is added under the '''Field Sensors''' node of the Navigation Tree. At the end of a SBR simulation, the field sensor nodes in the Navigation Tree become populated by the magnitude and phase plots of the three vectorial components of the electric ('''E''') and magnetic ('''H''') field as well as the total electric and magnetic fields.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Data_Visualization_and_Processing#Visualizing_3D_Near-Field_Maps | Visualizing 3D Near Field Maps]]'''.
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<table>
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<td> [[Image:PROP18M.png|thumb|360px|Computed total electric field distribution of a vertical short dipole radiator 2m above the default global ground at 1GHz.]] </td>
<td> [[Image:PROP18N.png|thumb|360px|Computed total magnetic field distribution of a vertical short dipole radiator 2m above the default global ground at 1GHz.]] </td>
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=== Computing Radiation Patterns In SBR ===
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[[File:PROP18(3).png|thumb|350px|EM.Terrano's Radiation Pattern dialog.]]
[[EM.Terrano]] lets you compute the effective far-field radiation pattern of your radiating structure in the presence of surrounding scatterers and obstructing objects. Computing the radiation pattern of an antenna or any radiating structure in [[EM.Cube]]'s full-wave computational modules like [[EM.Tempo]], [[EM.Picasso]] or [[EM.Libera]] is fairly straightforward. Using [[EM.Illumina]] you can use an asymptotic physical optics solver to model the effects of the mounting platform on the performance of an installed antenna. Computing radiation patterns in [[EM.Terrano]] may not seem intuitive at first because you have to import the radiation patterns from external data files after all.
In order to visualize a radiation pattern in [[EM.Terrano]], you have to define a "Far Fields" observable. To do so, right-click on the '''Far Fields''' item in the '''Observables''' section of the navigation tree and select '''Insert New Radiation Pattern...''' from the contextual menu. This opens up the Radiation Pattern dialog. You can accept most of the default settings. The most important [[parameters]] to change are the angular resolutions. These are called '''Theta Angle Increment''' and '''Phi Angle Increment''', both of which have default values of 5°. When you define a far-field observable in [[EM.Terrano]], a collection of <u>invisible</u>, isotropic receivers are placed on the surface of a large sphere that encircles your propagation scene and all of its geometric objects. These receivers are equally spaced placed uniformly on the spherical surface at a spacing that is determined by your specified angular resolutions. In most cases, you need to define angular resolutions of at least 1° or smaller. Note that this is different than the transmitter rays' angular resolution. You may have a large number of transmitted rays but not enough receivers to compute the effective radiation pattern at all 3D azimuth and elevation angles. Also keep in mind that with 1° Theta and Phi angle increments, you will have a total of 181 × 361 = 65,341 spherically placed receivers in your scene.
{{Note| Computing radiation patterns using [[EM.Terrano]]'s SBR solver typically takes much longer computation times than using [[EM.Cube]]'s other computational modules.}}
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Data_Visualization_and_Processing#Visualizing_3D_Radiation_Patterns | Visualizing 3D Radiation Patterns]]'''.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Data_Visualization_and_Processing#2D_Radiation_and_RCS_Graphs | Plotting 2D Radiation Graphs]]'''.
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