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{{Note|EM.Terrano is the ray tracing '''[[Propagation Module]]''' of '''[[EM.Cube]]''', a comprehensive, integrated, modular electromagnetic modeling environment. EM.Teranno 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.}}

=== The Importance of Physics-Based Site-Specific Propagation Modeling===

In a free-space line-of-sight (LOS) communication system, the signal propagates directly from the transmitter to the receiver without encountering any obstacles (scatterers). Free-space line-of-sight channels are ideal scenarios that can typically be used to model aerial or space communication system applications.

[[Image:multi1_tn.png|thumb|500px|A multipath propagation scene showing all the rays arriving at a particular receiver.]]

# Diffraction from an edge between two conjoined locally flat surfaces

=== A Note on the Pros and Cons of EM.Terrano's SBR Solver ===

* '''[[#Defining_Base_Point_Sets|Base Points]]''': are used to locate a single transmitter or receiver or arrays of transmitters or receivers in the scene.

In EM.Terrano, the various scene elements like buildings, terrain objects and base points are grouped together based on their type. All the objects listed under a particular group in the navigation tree share the same color, texture and material properties. Once a new block group has been created in the navigation tree, it becomes the "Active" group of the project workspace, which is always displayed in bold letters. You can start drawing new objects under the active node. Any block group can be made active by right-clicking on its name in the navigation tree and selecting the '''Activate''' item of the contextual menu.

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[[Image:prop_manual-12_tn.png|thumb|500px|An imported external terrain model.]]

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 Field Solver|asymptotic field solver]].

=== Using EM.Terrano as a Field Solver ===

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.

=== Defining Transmitter Sets ===

A transmitter is a point radiator with a fully defined polarimetric radiation pattern over the entire 3D space in the spherical coordinate system. You can model a radiating structure using [[EM.Tempo|EM.TEmpo]], [[EM.Picasso]], [[EM.Libera]] or [[EM.Illumina]] and generate a 3D radiation pattern data file for it. These data are stored in a specially formatted file with a "'''.RAD'''" file extension. It contains columns of spherical φ and θ angles as well as the real and imaginary parts of the complex-valued far field components '''E_θ''' and '''E_φ'''. The θ- and φ-components of the far-zone electric field determine the polarization of the transmitting radiator.

To define a transmitter source in EM.Terrano, first you need to have at least one '''Base Point''' in your project workspace. Follow the procedure below:

EM.Terrano's SBR ray tracer uses a method known as Geometrical Optics (GO) in conjunction with the Uniform Theory of Diffraction (UTD) to traces the rays from their originating point at the source to the individual receiver locations. Ray may hit obstructing objects on their way and get reflected, diffracted or transmitted. EM.Terrano's SBR solver can only handle diffraction off linear edges and reflection from and transmission through planar material interfaces. The underlying theory for calculation of reflection, transmission and diffraction coefficients indeed assumes material media of infinite extents. When a ray hits a specular point on the surface of the obstructing object, a local planar surface assumption is made at the specular point.

If your propagation scene contains only cubic buildings on the flat global ground, the assumptions of linear edges and planar facets hold well although they violate the infinite extents assumption. In many practical scenarios, however, your buildings may have curved surface or the terrain may be irregular. EM.Terrano allows you to draw any type of surface or solid CAD objects under impenetrable and penetrable surface groups or penetrable volumes. Some of these objects contain curved surfaces or curved boundaries and edges such as cylinders, cones, etc. In order to address all such cases in the most general context, EM.Terrano always uses a triangular surface mesh of all the objects in your propagation scene. Even rectangular facets of cubic buildings are meshed using triangular cells. This is done to be able to properly discretize composite buildings made of conjoined cubic objects.

{{Note| EM.Terrano's frequency sweep simulations are very fast because the geometrical optics (ray tracing) part of the simulation is frequency-independent.}}

== Working with SBR Simulation Data ==

At the end of an SBR simulation, you can visualize the field maps and receiver power coverage map of your receiver sets. A coverage map shows the total '''Received Power''' by each of the receivers and is visualized as a color-coded intensity plot. Under each receiver set node in the navigation tree, a total of seven field maps together with a received power coverage map are added. The field maps include amplitude and phase plots for the three X, Y, Z field components plus a total electric field plot. To display a field or coverage map, simply click on its entry in the navigation tree. The 3D plot appears in the Main Window overlaid on your propagation scene. A legend box on the right shows the color scale and units (dB). The 3D coverage maps are displayed as horizontal confetti above the receivers. You can change the appearance of the receivers and maps from the property dialog of the receiver set. You can further customize the settings of the 3D field and coverage plots.

At the end of a frequency sweep or parametric sweep SBR simulation, as many coverage maps as the number of sweep variable samples are generated and added to the navigation tree. In this case the additional seven field maps are saved to avoid a cluttered navigation tree. You can click on each of the coverage maps corresponding to each of the variable samples and visualize it in the project workspace. You can also animate the coverage maps on the navigation tree.

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in ASCII data files called "PREC_i.DAT", "PL_i.DAT" and "SNR_i.DAT", where is the index of the receiver set in your scene. These quantities are tabulated vs. the sweep variable's samples. You can plot these files in EM.Grid.

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