Changes

The new EM.Terrano 2013 has been totally reconstructed based on our integrated [[EM.Cube ]] software foundation. This integration has created the opportunity to inject a host of new powerful features such as a highly customizable terrain generator, DEM terrain import, complex building constructions, and versatile interior wall arrangements for indoor propagation modeling. As a result of this seamless interface with [[EM.Cube]]'s other modules, you can now model complex antenna systems in [[EM.Picasso]], [[EM.Tempo]] or [[EM.Libera]], and generate antenna radiation patterns than can be used to model directional transmitters and receivers at the two ends of your propagation channel. Conversely, you can analyze a propagation scene in EM.Terrano and import the rays received at a certain receiver location as coherent plane wave sources to [[EM.Picasso]], [[EM.Tempo]] or [[EM.Libera]]. You can also model periodic wall or ground structures using the periodic simulation capability of [[EM.Picasso]] or [[EM.Tempo]] and generate macromodels for their reflection and transmission coefficients as functions of the ray incidence angles. You can then define buildings or terrains in your propagation scene that are governed by such macromodels.

The different rays arriving at a receiver location create constructive and destructive interference patterns. This is known as the multipath effect. This together with the shadowing effects caused by building obstructions lead to channel fading. In many wireless applications, the total received power by the receiver is all that matters. In some others, the angle of arrival of the rays as well as their polarization are of immense interest. A fully polarimetric, coherent ray tracer like [[EM.Cube]]'s Shooting-and-Bouncing-Rays (SBR) solver lets you compute and resolve all the rays received by a receiver including their power levels, time delays and angles of arrival.

[[EM.Cube]]'s [[Propagation Module]] provides an asymptotic ray tracing simulation engine that is based on a technique known as Shooting-and-Bouncing-Rays (SBR). In this technique, propagating spherical waves are modeled as ray tubes or beams that emanate from a source, travel in space, bounce from obstacles and are collected by the receiver. As rays propagate away from their source (transmitter), they begin to spread (or diverge) over distance. In other words, the cross section or footprint of a ray tube expands as a function of the distance from the source. [[EM.Cube ]] uses an accurate equi-angular ray generation scheme to that produces almost identical ray tubes in all directions to satisfy energy and power conservation requirements.

[[EM.Cube ]] discretizes all the objects of the scene into flat triangular facets. Obviously, rectangular and cubic objects preserve their geometric shapes through this discretization. Objects with curved surfaces such as cylinders, cones or spheres, are approximated by "polymesh" representations. The geometric fidelity of the resulting mesh depends on the specified mesh edge length. When a ray hits a triangular facet, the propagating spherical wave is approximated as a plane wave at the specular point. The reflection and transmission coefficients of the surface are calculated at the operational frequency and at the particular ray incident angle.

[[EM.Cube]]'s SBR simulation engine can be used as a versatile and powerful asymptotic electromagnetic (EM) solver. If you compare [[EM.Cube]]'s [[Propagation Module]] with its other computational modules, you will notice a lot of similarities. While other modules group objects primarily by their material properties, [[Propagation Module]] categorizes the types of obstructing surfaces. Besides sharing the same ray-surface interaction mechanisms, all the objects belonging to a surface group also share the same material properties. [[Propagation Module]] offers similar source types and similar observable types as the other computational modules. For instance, the Hertzian dipole sources used in a SBR simulation are identical to those offered in PO, MoM3D and Planar modules. The plane wave sources are identical across all computational modules. [[Propagation Module]]'s sensor field planes, far field observables (either radiation patterns or RCS) and Huygens surfaces are all fully compatible with [[EM.Cube]]'s other computational modules.

[[EM.Cube]]'s new SBR simulation engine utilizes an intelligent ray tracing algorithm based on the concept of k-dimensional trees. A k-d tree is a space-partitioning data structure for organizing points in a k-dimensional space. k-d trees are particularly useful for searches that involve multidimensional search keys such as range searches and nearest neighbor searches. In a typical large radio propagation scene, there might be a large number of rays emanating from the transmitter that may never hit any obstacles. For example, upward-looking rays in an urban propagation scene quickly exit the computational domain. Rays that hit obstacles on their path, on the other hand, generate new reflected and transmitted rays. The k-d tree algorithm traces all these rays systematically in a very fast and efficient manner. Another major advantage of k-d trees is the fast processing of multi-transmitters scenes. Unlike the previous versions of the SBR solver which could handle one transmitter at a time and would superpose all the resulting rays at the end of the simulation, the new SBR shoots rays from all the transmitters at the same time.

[[EM.Cube]]'s new SBR simulation engine performs fully polarimetric and coherent SBR simulations with arbitrary transmitter antenna patterns. The new engine solves directly for the vectorial field components at the receiver locations or field observation points. This is far more rigorous than the previous versions of the SBR solver which primarily utilized ray power calculations based on the two vertical and horizontal polarizations. In other words, [[EM.Cube]]'s new SBR engine is a truly asymptotic "field" solver. As a result, you can visualize the magnitude and phase of all six electric and magnetic field components at any point in the computational domain. For power calculations at the receiver location, an isotropic, polarization-matched, receiving antenna is assumed.

In most scenes, the buildings and the ground or terrain can be assumed to be made of homogeneous materials. These are represented by their electrical properties such as permittivity e and electric conductivity s. More complex scenes may involve a multilayer ground or multilayer building walls. In such cases, one can no longer use the simple reflection or transmission coefficient formulas for homogeneous medium interfaces. [[EM.Cube ]] calculates the reflection and transmission coefficients of multilayer structures as functions of incident angle, frequency and polarization and uses them at the respective specular points.

In order to maintain a high computational speed for urban propagation problems, [[EM.Cube]]'s SBR solver ignores double diffractions. Recall that diffractions from edges give rise to a large number of new secondary rays. The power of diffracted rays drops much faster than reflected rays. [[EM.Cube ]] ignores diffracted rays that are not detected by any receiver. In other words, an edge-diffracted ray does not diffract again from another edge. However, reflected and penetrated rays do get diffracted from edges just as rays emanated directly from the sources do.

An [[EM.Cube ]] propagation scene typically consists of several elements. At a minimum, you need a transmitter (Tx) at some location to launch rays into the scene and a receiver (Rx) at another location to receive and collect the incoming rays. A transmitter and a receiver together make the simplest propagation scene, representing a free-space line-of-sight (LOS) channel. A transmitter is one of [[EM.Cube]]'s several source types, while a receiver is one of [[EM.Cube]]'s several observable types. A simpler source type is a Hertzian dipole. A simpler observable is a field sensor that is used to compute the electric and magnetic fields on a specified plane.

Figure 1: The Navigation Tree of [[EM.Cube]]'s [[Propagation Module]].

[[EM.Cube ]] has generalized the concept of '''Block''' as any object that obstructs and affects radio wave propagation. Rays hit the facets of a block and bounce off the surface of those facets or penetrate them and continue their propagation. Rays also get diffracted off the edges of these blocks. In [[EM.Cube]]'s [[Propagation Module]], blocks are grouped together by the type of their interaction with rays. [[EM.Cube ]] currently offers three types of blocks for use in a propagation scene:

[[EM.Cube]]'s [[Propagation Module]] allows you to define block groups of each of the above three types. Each block group has the same color or texture and its members share the same material properties: permittivity ε_r and conductivity σ. Also, all the penetrable surfaces belonging to the same block group have the same wall thickness. You can define many different block groups with certain properties and underneath each introduce many member objects with different geometrical shapes and dimensions. The table below summarizes the characteristics of each block type:

In outdoor propagation scenes such as "Urban Canyons", you are primarily interested in the wireless coverage in the areas among buildings. You can assume that rays bounce off the exterior walls of these buildings but do not penetrate them. In other words, you ignore the transmitted rays and assume that they are either absorbed or diffused inside the buildings. This is not an unrealistic assumption. [[EM.Cube ]] offers "Impenetrable Blocks" to model buildings in outdoor propagation scenes. A penetrable block has a color or texture property as well as material properties: permittivity (e_r) and conductivity (s). By default, a brick building is assumed with ε_r = 4.4 and σ = 0.001 S/m. Impinging rays are reflected from the facets of impenetrable buildings or diffracted from their edges.

Under an impenetrable block group, you can draw any of [[EM.Cube]]'s native solid or [[Surface Objects|surface objects]] or you can import external model files like STEP, IGES or STL. You can change the properties of an impenetrable surface. In the property dialog of the surface group, click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog. In this dialog, you can change the name of the material and its permittivity and electric conductivity. The box labeled "Specify Loss Tangent" is unchecked by default. If you check it, you can specify the '''Loss Tangent''' of the material, which, in turn, updates the value of electric conductivity at the center frequency of the project. You can also use [[EM.Cube]]'s Material List, which will be explained later.

A typical indoor propagation scene usually involves an arrangement of walls that represent the interior of a building. The transmitters and receivers are then placed in the spaces among such walls. From the point of view of [[EM.Cube]]'s SBR simulator, walls act like thin penetrable surfaces. [[EM.Cube ]] uses the "Thin Wall Approximation" to model penetrable surfaces. It assumes that rays simply penetrate a wall and exit at the same specular point on the opposite side of the wall. In other words, rays are not displaced by the walls, nor do they get trapped inside the walls (no internal reflection). This is equivalent to assuming a zero thickness for penetrable surfaces for the purpose of geometrical ray tracing, while the finite thickness of the "thin" surface is used for electromagnetic calculation of transmission coefficient. [[EM.Cube ]] offers "Penetrable Surface Blocks" for the construction of rooms in indoor propagation scenes as well as modeling of hollow buildings and other structures. You can define many penetrable surface groups with arbitrary thicknesses and material properties (color, texture, permittivity and electric conductivity).

Under a penetrable surface group, you can draw any of [[EM.Cube]]'s native solid or [[Surface Objects|surface objects]] or you can import external model files like STEP, IGES or STL. You can change the properties of a penetrable surface group including its default thickness. In the property dialog of the surface group, click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog. Similar to the case of impenetrable surfaces, from this dialog, you can change the material properties (permittivity and electric conductivity) as well as '''Thickness''', which is expressed in the project units. You can also use [[EM.Cube]]'s Material List, which will be explained later.

You can construct several thin walls and arrange them as rooms. A regular room can be built by placing four vertical wall objects together with an optional horizontal wall at the top for the ceiling. Alternatively, you may use [[EM.Cube]]'s hollow box objects or boxes with one or two capped end(s). '''Keep in mind that all the penetrable surfaces belonging to a group have the same wall thickness, which is initially set to 0.5 project units by default. Also, note that solid CAD objects belonging to a penetrable surface group are treated as air-filled hollow structures.''' The thickness of penetrable surfaces is implied and not visualized when displaying objects in the project workspace.

The size of the Ray domain is specified in terms of six '''Offset''' [[parameters ]] along the ±X, ±Y and ±Z directions. The default value of all these six offset [[parameters ]] is 10 project units. You can change them arbitrarily. After changing these values, use the '''Apply''' button to make the changes effective while the dialog is still open.

Most outdoor and indoor propagation scenes include a flat ground at their bottom, which bounces incident rays back into the scene. [[EM.Cube]]'s [[Propagation Module]] provides a global flat ground at z = 0. The global ground indeed acts as an impenetrable surface that blocks the entire computational domain from the z = 0 plane downward. It is displayed as a translucent green plane at z = 0 extending downward. The color of the ground plane is always the same as the color of the ray domain. The global ground is assumed to be made of a homogeneous dielectric material with a specified permittivity ε_r and electric conductivity σ. By default, a rocky ground is assumed with ε_r = 5 and σ = 0.005 S/m. You can remove the global ground, in which case, you will have a free space scene. To disable the global ground, open up the Global Ground Settings Dialog, which can be accessed by right clicking on the '''Global Ground''' item in the Navigation Tree and selecting '''Global Ground Settings... '''Remove the check mark from the box labeled '''"Include Half-Space Ground (z<0)"''' to disable the global ground. This will also remove the green translucent plane from the bottom of your scene. You can also change the material properties of the global ground and set new values for the permittivity and electric conductivity of the impenetrable, half-space, dielectric medium. '''Do not forget to disable the global ground if you want to model a free space propagation scene.'''

A terrain surface acts as a custom, unlevel or irregular ground for your propagation scene. [[EM.Cube]]'s default global ground blocks the z < 0 half-space everywhere in the computational domain. You can simply turn off the global ground and create one or more terrain objects and place them arbitrarily in the scene. You can also import an external terrain model or file. A terrain represents an impenetrable surface with a more complex surface profile. You can have one or more terrain objects of finite extents and place them on or above the global ground.

# While impenetrable blocks can be created using any of [[EM.Cube]]'s solid or surface CAD object creation tools, terrain objects are created either using [[EM.Cube]]'s '''Terrain Generator''' or by importing an external terrain file. # Terrain objects belong to a special type of CAD objects called "Tessellated Objects", which differ from other regular CAD [[Surface Objects|surface objects]] or [[EM.Cube]]'s polymesh surfaces.

You can change the properties of a terrain surface group from its property dialog. Click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog, which is identical to the case of impenetrable surfaces. You can also use [[EM.Cube]]'s Material List, which will be explained later. When a new terrain type is created, its node on the Navigation Tree becomes active. Under this node you can create and add new terrain objects. When a terrain node is active for drawing, all CAD object creation tools are disabled. You have three options for creating a new terrain object, which will be described in detail in the next sections of this manual:

# Use [[EM.Cube]]'s '''Terrain Generator'''.

[[EM.Cube ]] provides a convenient and powerful Terrain Generator for creating a variety of terrain [[Surface Objects|surface objects]]. [[EM.Cube]]'s Terrain Generator looks very similar to [[CubeCAD]]'s Surface Generator. However, whereas the Surface Generator creates a generic or polymesh surface object, Terrain Generator always creates another special type of object known as a '''Tessellated Object'''. A terrain object is much simpler than [[EM.Cube]]'s polymesh objects and is usually made up of triangular or quadrilateral facets. As such, terrain objects have limited editing capabilities. For example, you can cut, copy, paste, translate or rotate terrain objects. But operations like scaling, mirroring, grouping (composite), arraying, exploding, linking or Boolean operations do not work on terrain objects.

Every time you create a new terrain object using Terrain Generator, an ASCII data file named "GeneratedTerrain" with a "'''.TRN'''" file extension is created and placed in your project folder. This is [[EM.Cube]]'s simple native terrain file format that basically lists all the (x, y, z) coordinates of the generated surface points on a horizontal, rectangular XY grid. Terrain Generator simply takes your custom function definition or one of the selected catalog surface types and generates the digital elevation data on the specified grid.

You can import two types of terrain in [[EM.Cube]]'s [[Propagation Module]]. The first type is "'''.TRN"''' terrain file, which is [[EM.Cube]]'s native terrain format. It is a basic digital elevation map with a very simple ASCII data file format. The resolution of the terrain map in the X and Y directions is specified in meters as STEPS. The (x, y, z) coordinates of the terrain points are then listed one point per line. The other type of terrain format supported by [[EM.Cube ]] is the standard '''7.5min DEM''' file format with a '''.DEM''' file extension.

To import an external terrain model, first you have to create a terrain group node in the Navigation Tree. Right click on the name of the terrain group in the Navigation Tree and select either '''Import Terrain...''' or '''Import DEM File...''' A standard [[Windows ]] '''Open Dialog''' opens up, with the file type set to .TRN or .DEM extensions, respectively. You can browse your folders and find the right terrain model file to import.

You can also export all the terrain objects in the project workspace as a terrain file with a '''.TRN''' file extension. You can even import a DEM terrain model from an external file and then save and export it as a native terrain (.TRN) file. To export the terrain, select '''File''' > '''Export...''' from [[Propagation Module]]'s '''File Menu'''. The standard [[Windows ]] Save Dialog opens up with the default file type set to '''.TRN'''. Type in a name for your new terrain file and click the '''Save''' button to export the terrain data.

In [[EM.Cube]]'s [[Propagation Module]], you can define multilayer surfaces with both reflection and transmission properties. You can define multilayer impenetrable buildings, multilayer penetrable walls, and multilayer terrain, with an arbitrary number of layers having different material compositions. You define a multilayer surface in the property dialog of a block, whether impenetrable, penetrable or terrain. In the section entitled '''Surface Type''', two options are available: '''Standard Material''' or '''User Defined Model'''. For simple multilayer walls, select the '''Standard Material''' option. You can add new layers with arbitrary thickness and material [[parameters ]] to the existing layers. To insert a new layer, deselect any items in the layer list, and click the '''Add/Edit''' button to open the "Add Layer" Dialog. Here you can enter a name for the new layer and values for its '''Thickness''', ε_r and σ. You may also delete any layer by selecting and highlighting it and clicking the '''Delete''' button. You can move layers up or down using the '''Move Up''' and '''Move Down''' buttons and change the layer hierarchy.

You can also search [[EM.Cube]]'s material database by clicking the '''Material''' button of "Add Layer" or "Edit Layer" dialogs. This opens the '''Materials''' Dialog. Inside the material list select and highlight any row and click the '''OK''' button. The selected material will fill out all the fields in the "Add Layer" or "Edit Layer" dialogs. Inside the Materials Dialog, you can type the few first letters of any material, and it will take you to the corresponding row of the list.

Figure: [[EM.Cube]]'s material list.

When you start a new project in [[EM.Cube]]'s [[Propagation Module]] and draw a solid object like a box in the project workspace without having defined any surface groups, it is assumed to be of the impenetrable surface type. A default impenetrable surface group called Block_1 is automatically added to the Navigation Tree, which holds your newly drawn object. The default group has the material properties of "Brick" (ε_r = 4.4 and σ = 0.001 S/m.) with a dark brown color. You can continue drawing new objects in the project workspace and adding them under this block node. Or you can define a new surface type with different properties. By default, the last surface group that was defined is '''Active'''. The current active surface group is always listed in bold letters in the Navigation Tree. When you draw a new object, it is always inserted under the current active surface group. Any surface group can be activated by right clicking its name in the Navigation Tree and selecting the '''Activate''' item of the contextual menu.

You can move any object from its current surface group into any other available surface group. First select the object, then right click on its surface and select '''MoveTo > Propagation >'''. A submenu appears which lists all the available surface groups where you can transfer the selected object. You can also move objects among surface groups by selecting their names in the Navigation Tree and using the contextual menu. In a similar way, you can transfer objects from [[Propagation Module]] to [[EM.Cube]]'s other modules or vice versa. '''Keep in mind that all the external model files such as STEP, IGES, STL, etc. are first imported to [[EM.Cube]]'s [[CubeCAD]], from which you can transfer them to other modules.''' First select the object, then right click and select '''MoveTo >'''. In the submenu you will see a list of all the [[EM.Cube ]] modules that have at least one available group where you can transfer your selected object. You can select multiple objects for transfer. When using the keyboard's '''Shift Key''' or '''Ctrl Key''' for multiple selection, make sure that those keys are held down, when you right click to access the contextual menu.

Like every other electromagnetic solver, [[EM.Cube]]'s SBR ray tracer requires a source for excitation and one or more observables for generation of simulation data. [[EM.Cube]]'s new [[Propagation Module]] offers several types of sources and observables for a SBR simulation. You can mix and match different source types and observable types depending on the requirements of your modeling problem. There are two types of sources:

The simplest SBR simulation can be performed using a short dipole source with a specified field sensor plane. In this way, [[EM.Cube ]] computes the electric and magnetic fields radiated by your dipole source in the presence of your multipath propagation environment. A &quot;classic&quot; urban propagation scene can be set up using a &quot;Transmitter&quot; source and an array of &quot;Receiver&quot; observables. A transmitter is a point radiator with a user defined radiation pattern. A receiver is a polarization-matched isotropic point radiator that collects the received rays at its aperture. Using receivers, you can calculate the received power coverage map of your propagation scene. You can also calculate your channel's path loss between the transmitter and all the receivers. <br />

Earlier versions of [[EM.Cube]]'s [[Propagation Module]] used to offer an isotropic radiator with vertical or horizontal polarization as the simplest transmitter type. This release of [[EM.Cube ]] has abandoned isotropic radiator transmitters because they do not exist physically in a real world. Instead, the default transmitter radiator type is now a Hertzian dipole. Note that before defining a transmitter, first you have to define a base set to establish the location of the transmitter. Most simulation scenes involve only a single transmitter. Your base set can be made up of a single point for this purpose.

In the &quot;Radiator&quot; section of the dialog, you have two options to choose from: &quot;Short Dipole&quot; and &quot;User Defined&quot;. The default option is short dipole. A short dipole radiator has a '''Length'''''dl'' expressed in project units, a current '''Amplitude''' in Amperes and a current '''Phase''' in degrees. The '''Direction''' of the dipole is determined by its unit vector that has three X, Y and Z components. By default, a Z-directed short dipole radiator is assumed. You can change all [[parameters ]] of the dipole as you wish. Keep in mind that all the transmitters belonging to the same set have parallel radiators with identical properties.

In order to tie up transmitters and receivers with CAD objects in the project workspace, [[EM.Cube ]] uses point objects to define transmitters and receivers. These point objects represent the base of the location of transmitters and receivers in the computational domain. Hence, they are grouped together as &quot;Base Sets&quot;. You can easily interchange the role of transmitters and receivers in a scene by switching their associated bases. The usefulness of concept of base sets will become apparent later when you place transmitters or receivers on an irregular terrain and adjust their elevation.

A short dipole is the closest thing to an omni-directional radiator. The direction or orientation of the short dipole determines its polarization. In many applications, you may rather want to use a directional antenna for your transmitter. You can model a radiating structure using [[EM.Cube]]'s FDTD, Planar, MoM3D or PO modules and generate a 3D radiation pattern data file for it. These data are stored in a specially formatted file with a &quot;'''.RAD'''&quot; extension, which contains columns of spherical &phi; and &theta; angles as well as the real and imaginary parts of the complex-valued far field components '''E_&theta;''' and '''E_&phi;'''. The &theta;- and &phi;-components of the far-zone electric field determine the polarization of the transmitting radiator.

To define a directional transmitter radiator, you need to select the &quot;User Defined&quot; option in the &quot;Radiator&quot; section of the Transmitter Dialog. You can do this either at the time of creating a transmitter set, or afterwards by opening the property dialog of the transmitter set. In the &quot;Custom Pattern [[Parameters]]&quot;, click the '''Import Pattern''' button to set the path for the radiation data file. This opens up the standard [[Windows ]] Open dialog, with the default file type or extension set to &quot;.RAD&quot;. Browse your folders to find the right data file. A radiation pattern file usually contains the value of &quot;Total Radiated Power&quot; in its file header. This is used by default for power calculations in the SBR simulation. However, you can check the box labeled &quot;'''Custom Power'''&quot; and enter a value for the transmitter power in Watts. [[EM.Cube ]] can also rotate the imported radiation pattern arbitrarily. In this case, you need to specify the '''Rotation''' angles in degrees about the X-, Y- and Z-axes. Note that these rotations are performed sequentially and in order: first a rotation about the X-axis, then a rotation about the Y-axis, and finally a rotation about the Z-axis.

[[EM.Cube]]'s SBR simulations are fully coherent and 3D-polarimetric. This means that the phase and polarization of all the rays are maintained and processed during their bounces in the scene. Your propagation scene can have more than one transmitter. During an SBR simulation, all the rays emanating from all the transmitters are traced in the propagation scene. All the received rays at a given receiver location are summed coherently and vectorially. This is based on the principle of linear superposition. All the transmitters belonging to the same transmitter set have the same radiation properties. They are either parallel short dipole radiators with the same current amplitudes and phases, or parallel user defined radiators with identical radiation patterns. As these transmitters are placed at different spatial locations, they effectively form an antenna array with identical elements. The array factor is simply determined by the coordinates of the base points. If you want to have different amplitude or phases, then you need to define different transmitter sets.

[[EM.Cube]]'s [[Propagation Module]] allows you to draw any type of surface or solid CAD objects under impenetrable and penetrable surface groups. Some of these objects have flat faces such as boxes, pyramids, rectangle or triangle strips, etc. Some others contain curved surfaces or curved boundaries such as cylinders, cones, etc. All the non-flat surfaces have to be discretized in the form of a collection of smaller flat facets. [[EM.Cube ]] uses a triangular surface mesh generator to discretize the penetrable and impenetrable [[Surface Objects|surface objects]] of your propagation scene. This mesh generator is very similar to the ones used in [[EM.Cube]]'s two other modules: MoM3D and Physical Optics (PO).

You can build a variety of surface and [[Solid Objects|solid objects]] using [[EM.Cube]]'s native &quot;Curve&quot; CAD objects like lines, polylines, circles, etc. You can use tools like Extrude, Loft, Strip-Sweep, Pipe-Sweep, etc. to transform curves into surface or [[Solid Objects|solid objects]]. '''However, keep in mind that all the &quot;Curve&quot; CAD objects are ignored by the SBR mesh generator and are therefore not sent to the simulation engine.'''

You can view and examine the discretized version of your scene objects as they are sent to the SBR simulation engine. To view the mesh, click the '''Mesh''' [[File:mesh_tool.png]] button of the Simulate Toolbar or select '''Simulate &gt; Discretization &gt; Show Mesh''', or use the keyboard shortcut '''Ctrl+M'''. A triangular surface mesh of your physical structure appears in the project workspace. In this case, [[EM.Cube ]] enters it mesh view mode. You can perform view operations like rotate view, pan, zoom, etc. But you cannot select objects, or move them or edit their properties. To get out of the Mesh View and return to [[EM.Cube]]'s Normal View, press the '''Esc Key''' of the keyboard, or click the Mesh button of the Simulate Toolbar once again, or go to the Simulate Menu and deselect the '''Discretization &gt;''' '''Show Mesh''' item.

You can adjust the mesh resolution and increase the geometric fidelity of discretization by creating more and finer triangular facets. On the other hand, you may want to reduce the mesh complexity and send to the SBR engine only a few coarse facets to model your buildings. To adjust the mesh resolution, open the Mesh Settings Dialog by clicking the '''Mesh Settings''' [[File:mesh_settings.png]] button of the Simulate Toolbar or select '''Simulate &gt; Discretization &gt;''' '''Mesh Settings...'''. This dialog provides a single [[parameters]]: '''Edge Length'''., which has a default value of 100 project units. If you are already in the Mesh View Mode and open the Mesh Settings Dialog, you can see the effect of changing the edge length using the '''Apply''' button. Click OK to close the dialog.

Note that unlike [[EM.Cube]]'s other computational modules that express the default mesh density based on the wavelength, the resolution of the SBR mesh generator is expressed in project length units. The default edge length value of 100 units might be too large for non-flat objects. You may have to use a lower value to capture the curvature of your curved structures adequately.

In [[EM.Cube]], terrain objects are represented by and saved as special &quot;Tessellated&quot; objects with quadrilateral cells. This is true of terrain objects that you create yourself using [[EM.Cube]]'s Terrain Generator as well as all the terrain objects that you import from external files to your project. The center of each cell represents the terrain elevation at that point. Tessellated objects are considered as discretized objects by [[EM.Cube ]] and they are not meshed one more time by the SBR mesh generator. Each quadrilateral cell is divided into two triangular cells before being passed to the SBR simulation engine. Therefore, when using [[EM.Cube]]'s Terrain Generator to create a new terrain object, you have to pay special attention to the resolution of the terrain object as it determines the total number of terrain facets sent to the simulation engine. A high resolution terrain, although looking better and more realistic, may easily lead to an enormous computational problem.

You can use [[EM.Cube]]'s &quot;Polymesh&quot; tool to discretize solid and surface CAD objects. You can manually control the mesh characteristics of polymesh objects including inserting new nodes on faces and edges or deleting existing nodes. In addition, [[EM.Cube]]'s Solid Generator and Surface Generator tools create ploymesh solids and surfaces, respectively. Like tessellated object, polymesh objects are also considered as discretized objects by [[EM.Cube ]] and they are not meshed again by the SBR mesh generator.

In [[EM.Cube]], buildings and all other CAD objects are initially created on the XY plane by default. In other words, the Z-coordinate of the local coordinate system (LCS) of all blocks is set to zero until you change them. As long as you use the global ground, all is fine as your buildings are seated on the ground. When your propagation scene has an irregular terrain, you want to place your buildings on the terrain and not buried under it. Buildings in [[EM.Cube ]] are not adjusted to the terrain elevation automatically. You need to instruct [[EM.Cube ]] to do so.

In [[EM.Cube]], all the transmitters and receivers are tied up with point objects in the project workspace. These point objects are grouped and organized in base sets. When you move the point objects or change their coordinates, all of their associated transmitters or receivers immediately follow them to the new location. For example, you usually define a grid of receivers using a base set that is made up of a uniformly spaced array of points and spread them in your scene. All of these receivers have the same height because their associated base points all have the same Z-coordinate. When your receivers are located above a flat terrain like the global ground, their Z-coordinates are equal to their height above the ground, as the terrain elevation is fixed and equal to zero everywhere. The same is true for transmitters, too.

In many propagation modeling problems, your transmitters and receivers may be located above an irregular terrain with varying elevation across the scene. In that case, you may want to place your transmitters or receivers at a certain height above the underlying ground. The Z-coordinate of a transmitter or receiver is now the sum of the terrain elevation at the base point and the specified height. [[EM.Cube ]] gives you the option to adjust the transmitter and receiver sets to the terrain elevation. This is done for individual transmitter sets and individual receiver sets. At the top of the Transmitter Dialog there is a check box labeled &quot;'''Adjust Tx Sets to Terrain Elevation'''&quot;. Similarly, at the top of the Receiver Dialog there is a check box labeled &quot;'''Adjust Rx Sets to Terrain Elevation'''&quot;. These boxes are unchecked by default. As a result, your transmitter sets or receiver sets coincide with their associated base points in the project workspace. If you check these boxes and place a transmitter set or a receiver set above an irregular terrain, the transmitters or receivers are elevated from the location of their associated base points by the amount of terrain elevation as can be seen in the figure below.

[[EM.Cube]]'s [[Propagation Module]] offers three types of ray tracing simulations:

# Set the unit of project scene and the frequency of operation. Note that [[EM.Cube]]'s default project unit is millimeter. When working with the [[Propagation Module]], pay attention to the project unit. Radio propagation problems usually require meter, mile or kilometer as the project unit.

There are a number of SBR simulation settings that can be accessed and changed from the SBR Settings Dialog. To open this dialog, click the button labeled '''Settings''' on the right side of the '''Select Engine''' dropdown list in the Run Dialog. [[EM.Cube]]'s SBR simulation engine allows you to separate the physical effects that are calculated during a ray tracing process. You can selectively enable or disable '''Ray Reflection''', '''Ray Transmission''' and '''Ray Diffraction'''. By default, all three effects are checked and included in the computations. Separating these effects sometimes help you better analyze your propagation scene and understand the impact of various blocks in the scene.

[[EM.Cube ]] requires a finite number of ray bounces for each original ray emanating from a transmitter. This is very important in situations that may involve resonance effects where rays get trapped among certain group of surfaces and may bounce back and forth indefinitely. This is set using the box labeled &quot;'''Max No. Ray Bounces'''&quot;, which has a default value of 10. Note that the maximum number of ray bounces directly affects the computation time as well as the size of output simulation data files. This can become critical for indoor propagation scenes, where most of the rays undergo a large number of reflections.

You can also view the ray [[parameters ]] by opening the property dialog of a receiver set. By default, the first receiver of the set is always selected. You can select any other receiver from the drop-down list labeled '''Selected Receiver'''. If you click the button labeled '''Show Ray Data''', a new dialog opens up with a table that contains all the received rays at the selected receiver and their [[parameters]]:

Besides visualizing the coverage map and received rays in the [[EM.Cube|EM.CUBE]]'s [[Propagation Module]], you can also plot the '''Path Loss''' of all the receivers belonging to a receiver set as well as the '''Power Delay Profile''' of individual receivers. To plot these data, go the '''Observables''' section of the Navigation Tree and right click on the '''Receivers''' item. From the context menu, select '''Plot Path Loss''' or '''Plot Power Delay Profile''', respectively. The path loss data between the active transmitter and all the receivers belonging to a receiver set are plotted on a Cartesian graph. The horizontal axis of this graph represents the index of the receiver. Power Delay Profile is a bar chart that plots the power of individual rays received by the currently selected receiver versus their time delay. If there is a line of sight (LOS) between a transmitter and receiver, the LOS ray will have the smallest delay and therefore will appear first in the bar chart. Sometimes you may have several rays arriving at a receiver at the same time, i.e. all with the same delay, but with different power level. These will appear as stacked bars in the chart.

You can also plot the path loss and power delay profile graphs and many others from [[EM.Cube|EM.CUBE]]'s data manager. You can open data manager by clicking the '''Data Manager''' [[File:data_manager_icon.png]] button of the '''Compute Toolbar''' or by selecting '''Compute [[File:larrow_tn.png]] Data Manager''' from the menu bar or by right clicking on the '''Data Manager''' item of the Navigation Tree and selecting Open Data Manager... from the contextual menu or by using the keyboard shortcut '''Ctrl+D'''. In the Data manager Dialog, you will see a list of all the data files available for plotting. These include the theta and phi angles of arrival and departure of the selected receiver. You can select any data file by clicking and highlighting its '''ID''' in the table and then clicking the '''Plot''' button.

By default, you run a single-frequency simulation in [[EM.Cube|EM.CUBE]]'s [[Propagation Module]]. You set the operational frequency of a SBR simulation in the project's '''Frequency Dialog''', which can be accessed in a number of ways:

You can also select the '''Frequency Sweep''' option in the '''Simulation Mode''' drop-down list of the '''Run Dialog'''. Click the '''Settings...''' button on the right side of this dropdown list to open up the Frequency Settings Dialog. Based on the original values of the project center frequency and bandwidth, the '''Start Frequency''' and '''End Frequency''' have default values. You can also change the '''Number of Samples'''. Once you click the '''Run''' button, [[EM.Cube|EM.CUBE ]] performs a frequency sweep by assigning each of the frequency samples as the current operational frequency and running the SBR simulation engine at that frequency. All the simulation data at all frequency samples are saved into the output data files including &quot;SBR_results.RTOUT&quot;. After the completion of a frequency sweep simulation, as many coverage maps as the number of frequency samples are generated and added to the Navigation Tree under the Receiver Set's entry. You can click on each of the coverage maps corresponding to each of the frequency samples and visualize it in the project workspace. You can also animate the coverage maps. To do so, right click on the receiver set's name in the Navigation Tree and select '''[[Animation]]''' from the contextual menu. The coverage maps start to animate by their order on the Navigation Tree. Once the entire list is displayed sequentially, it starts all over again from the beginning of the list. During the [[animation]], the '''[[Animation ]] Controls''' dialog appears at the lower right corner of the screen. This dialog has a number of buttons for pause/resume, step forward/backward, and step to the end/start. The title of each coverage map is shown in the box labeled '''Sample''' as it is displayed in the main window. You can also change the speed of [[animation]]. The default frame duration has a value of 300 (3x100) milliseconds. To stop the [[animation]], simply press the keyboard's '''Esc Key'''.

Multiple coverage maps on the Navigation Tree at the end of a frequency sweep and starting an [[animation ]] from the contextual menu.

[[Animation ]] controls dialog in the project workspace.

In [[EM.Cube|EM.CUBE]], all the CAD object properties as well as certain source, material and mesh [[parameters ]] can be assigned as [[variables]]. [[Variables]] are defined to control and vary the values of such [[parameters ]] either for editing purposes or to run parametric sweep or [[optimization]]. Variable are defined using the '''[[Variables]] Dialog''', which can be accessed in the three ways:

Next, you have to attach the variable to the CAD object. In this case, the CAD object is the point object that represents the transmitter's radiator. To attach a variable to a CAD object, open the object's property dialog and type in the name of the variable as the value of a property or parameter. In this case, the variable Tx_Height is going to control the Z-Coordinate of the point object. Once the value of the object parameter is replaced by the name of an already defined variable, it is updated with the current value of that variable. In the case of a variable of &quot;Uniformly Spaced Samples&quot; type, the current value is the start value. This value will be incrementally varied during a parametric sweep simulation process. Note that a variable can take a fixed value or a discrete set of values, too. You can always open the [[variables]] dialog and change the value or syntax of any variable. To make a new or modified value effective, click the '''Apply''' button of the [[variables]] dialog. You can test the values by performing a '''Dry Run''' of the selected variable. This runs an [[animation ]] of the project workspace as the value of the variable changes and all the related CAD objects are updated accordingly. Note that you can attach the same variable to more than one CAD object property or to the properties of different objects. You can also define multiple values or syntaxes to the same variable. To do so, open the '''Add Variable/Syntax Dialog''', and instead of typing in a new variable name, choose an existing variable name from the '''Name''' dropdown list. This will add a new value or syntax to the existing syntax(es) of the selected variable. When you return to the [[variables]] dialog, [[variables]] with more than one value or syntax will have a dropdown list in the '''Syntax''' column. You can choose any of these values or syntaxed at any time and make the change effective by clicking the '''Apply''' button.

To run a parametric sweep, open the '''Run Dialog''' and select the '''Parametric Sweep''' option in the '''Simulation Mode''' drop-down list. If you have not defined any [[variables]] in the project, the box in the '''[[Variables]]''' row before the '''View''' will be red. You have to turn it into green before you can run a simulation. By clicking the '''View''' button, you can open up the [[variables]] dialog from here. Once you click the '''Run''' button, [[EM.Cube|EM.CUBE ]] performs a parametric sweep by incrementally varying the values of all the defined [[variables]] from their start to stop values at the specified steps and updating all the related CAD objects. After the completion of a parametric sweep simulation, as many coverage maps as the total number of variable samples are generated and added to the Navigation Tree under the receiver set's entry. You can click on each of the coverage maps and visualize it in the project workspace. You can also animate the coverage maps sequentially. To do so, right click on the receiver set's name in the Navigation Tree and select '''[[Animation]]''' from the contextual menu. To stop the [[animation]], simply press the keyboard's '''Esc Key'''.

Choosing parametric sweep as the simulation mode in the run dialog. Note that one variable has been defined and [[EM.Cube|EM.CUBE ]] is ready to run the simulation.

[[EM.Cube|EM.CUBE]]'s coverage maps display the received power at the location of all the receivers. The receivers together from a set/ensemble, which might be uniformly spaced or distributed across the propagation scene or may consist of randomly scattered radiators. Every coverage map shows the '''Mean''' and '''Standard Deviation''' of the received power for all the receivers involved. These information are displayed at the bottom of the coverage map's legend box and are expressed in dB.