EM.Terrano Tutorial Lesson 2: Analyzing An Outdoor Multipath Propagation Scene
What You Will Learn
In this tutorial you will define impenetrable and penetrable surface blocks to model your building objects. You will learn how to define material properties of buildings and how to create CAD objects of different geometrical shapes to represent buildings. You will also investigate EM.Terrano’s facet mesh generator. In the last part of the tutorial lesson, you will explore the effect of changing the polarization of the transmitter antenna.
Constructing the Brick Buildings
In EM.Terrano, objects are organized into groups based on their type of interaction with incident rays. For example, EM.Terrano offers impenetrable and penetrable surfaces, terrain surfaces and penetrable volumes. Impenetrable surfaces are used to model buildings and other wave scatterers or obscurants that reflect and diffract incoming rays but they do not let rays to pass through. Both solid and surface CAD objects like boxes, cylinders, rectangle strips, etc., can be defined under an impenetrable surface group. It is assumed that inside a solid impenetrable object, there are many diffusion or absorption mechanisms that dissipate all the penetrated rays internally before letting them exit the object. All the objects belonging to the same impenetrable surface group share the same material properties, which include relative permittivity (εr), electric conductivity (σ) and a color.
Penetrable surface reflect and diffract incident rays, but the also transmit rays at the specular point. EM.Terrano indeed treats a penetrable surface as a thin wall. The transmitted ray at the other side of the thin wall continues to propagate in the free space. Similarly, all the objects belonging to the same penetrable surface group share the same material properties, which include relative permittivity (εr), electric conductivity (σ), a color as well as a wall thickness.
To define an impenetrable surface group, right-click on the Impenetrable Surfaces item in the Physical Structure section of the navigation tree and select Insert New Block… from the contextual menu. This opens up the Impenetrable Surface dialog, with a default label Block_1. The default color is dark brown and the default material is “Brick” with the relative permittivity εr = 4.44 and electric conductivity σ = 10-3S/m. For now, accept the default material settings.
When you return to the project workspace, you will notice that a new node called “Block_1” has been added to the navigation tree under the impenetrable surfaces item. Since Block_1 is the last group you created in the navigation tree, it is now the active group and its name is displayed in bold letters. This means that any CAD object you draw in the project workspace will belong to the Block_1 group. In other words, all the new drawn objects will be dark brown, impenetrable, brick surfaces.
With the Box tool selected, click on a blank space in the project workspace and drag the mouse to draw the rectangular base of your box object. Your building should have the dimensions: 40m × 30m × 10m. A property dialog pops up at the lower right corner of your screen. As you drag the mouse, you will see that the X-dimension and Y-dimension of your new object continuously change. When the base reaches a size of 40m × 30m or something close to that, click the mouse. Next, you have to give the right height to your box. Drag the mouse upward until you reach a height (Z-dimension) of 10m. Then, click once more (i.e. drop the mouse). At this time, the drawing of your box is complete. You will notice six small red balls on the six faces of the box object. These are called edit handles and can be used to change the dimensions of the box. Or you can simply type in any value for the X-, Y- and Z-dimensions of your box. Next, you have to position your building in the right location. If the box’s property dialog is still open, enter 0, 80m and 0 for the X-, Y- and Z-Coordinate of the box object, respectively. This will establish the center of the local coordinate system (LCS) of the box object (i.e. its base center) at the point (0, 80m, 0).
In the same way, draw a second box object with dimensions 30m × 50m × 10m and set its LCS coordinates at (-60m, 0, 0).
With the cylinder tool selected, click on a blank space in the project workspace and drag the mouse to draw the circular base of your cylinder object. Your new building should have a radius of 20m. A property dialog pops up on the lower right corner of your screen. As you drag the mouse, you will see that the base radius value continuously changes. When the base reaches a size of 20m or something close to that, click the mouse. Next, you have to give the right height to your cylinder. Drag the mouse upward until you reach a height (Z-dimension) of 25m. Then, drop the mouse. You will see a dark brown cylinder in the project workspace with a number of red edit handles on its base and top. Next, you have to move the new cylinder to the location. Set the LCS center of the cylinder to the point (30m, -60m, 0).
Next, define a penetrable surface group by right-clicking on the Penetrable Surfaces item in the Physical Structure section of the navigation tree and selecting Insert New Block… from the contextual menu. This opens up the Penetrable Surface dialog, with a default label Block_2. The default color is light brown and the default material is “Brick” again. For now, accept the default material settings. Note that the wall thickness will be 0.5m for all the objects belonging to this block group.
With the penetrable surface group Block_2 active in the navigation tree, draw the third box object with dimensions 60m × 40m × 20m and set its LCS coordinates at (120m, 0, 0).
The table below summarizes the properties of the four building objects you drew:
|Object||Geometry||Block Group||Surface Type||Material||Dimensions||Location Coordinates||Rotation Angles|
|Box_1||Box||Block_1||Impenetrable surface||Brick||40m × 30m × 10m||(0, 80m, 0)||(0°, 0°, 0°)|
|Box_2||Box||Block_1||Impenetrable surface||Brick||30m × 50m × 10m||(-60m, 0, 0)||(0°, 0°, 0°)|
|Box_3||Box||Block_2||Penetrable surface||Brick||60m × 40m × 20m||(120m, 0, 0)||(0°, 0°, 0°)|
|Cylinder_1||Cylinder||Block_1||Impenetrable surface||Brick||R = 20m, H = 25m||(30m, -60m, 0)||(0°, 0°, 0°)|
Defining the transmitter & Receivers
Similar to the previous tutorial lesson, define two base location sets called "BasePointSet_1" and "BasePointSet_2" with the colors blue and orange, respectively. Note that the last defined group remains as the active group in the project workspace. Select "BasePointSet_1" in the navigation tree, right-click on it and select Activate from the contextual menu. Under "BasePointSet_1", create a single point object for the transmitter. Under "BasePointSet_2", create an array of base points for the receiver set according to the tables below:
|Part||Object Type||Object Group||Group Color||Dimensions||Coordinates|
|Point_1||Point||Base_Point_1||Blue||N/A||(0, 0, 1.5m)|
|Point_2||Point||Base_Point_1||Orange||N/A||(-100m, -100m, 1.5m)|
|Array Object||Parent Object||X Count||Y Count||Z Count||X Spacing||Y Spacing||Z Spacing|
Define a new transmitter set associated with BasePointSet_1. Accept all the default settings for the transmitter set. Similarly, define a new receiver set associated with BasePointSet_2 and keep all the default settings of the receiver set. At this time, your project workspace must show a scene like the opposite figure.
Discretizing the Scene & Running an SBR Analysis
EM.Terrano uses a triangular surface mesh generator to discretize all the objects in the project workspace. This discretization is needed because the EM.Terrano's SBR simulation engine uses a locally flat representation of surfaces for the calculation of reflection and transmission coefficients. The facet mesh generator discretizes objects based on a “Cell Edge Length” parameter. This length is expressed in the project units and determines the approximate size of the triangular cells’ three sides. Its default value is 10 project units. You can set this parameter by clicking the Mesh Settings button of the Simulate Toolbar or using the keyboard shortcut Ctrl+G or via the menu item Simulate → Discretization → Mesh Settings to open the SBR Mesh Settings Dialog. For this tutorial, you will accept the default mesh settings.
To view the triangular surface mesh of your buildings, click the Show/Generate Mesh button of the Simulate Toolbar or alternatively use the keyboard shortcut Ctrl+M. Note how the cylindrical object has been discretized into a number of flat triangular facets. In general, the mesh view shows how the simulation engine sees your physical structure. In the mesh view mode, you can perform view operations such as rotate view, zoom in/out or pan view, but you cannot select objects or edit them. To exit the mesh view mode and return to the normal view mode, use the keyboard’s Esc key or click the Show/Generate Mesh button of the Simulate Toolbar one more time.
At this time, run a quick SBR analysis of your propagation scene and visualize the received power coverage map. You will notice a pattern of rings centered around the location of the transmitter. These rings are due to constructive and destructive interference of the ground-reflected rays with direct rays.
A lot of time the buildings may obscure the view of a coverage map. You can hide any EM.Cube object or freeze it. In the freeze state, you will only see a wireframe outline of the object. To freeze an individual object, right-click on its surface in the project workspace or right-click on its name in the navigation tree and select Freeze from the contextual menu. To unfreeze an object, repeat the same procedure. You can also freeze all the objects belonging to a particular material or block group. In the case, you need to freeze the entire group using its contextual menu. From the coverage map below, you can see that the receiver power of all the receivers located inside the impenetrable buildings is zero, while the receivers inside the building called Box_3 have significant power levels as if the building walls didn't exist. Also pay attention to the diffraction patterns in the shadow areas of the impenetrable buildings. In this case, the diffracted fields are the only fields that reach these shadow regions.
Changing the Material Composition of the Penetrable Building
In this part of the tutorial lesson, you are going to choose a different material with more electric losses for the penetrable building. Open the property dialog of the group called "Block_2" by right-clicking on its name in the navigation tree and selecting Properties... from the contextual menu. In the table at the bottom of the dialog, select and highlight the "brick" thin wall row and click the Add/Edit button of the dialog. This opens up the "Edit Layer" dialog. Click the Material button to open EM.Cube's materials list. Type the letter "w" on your keyboard to take you to the bottom of the table where the material names start with that letter. Choose the item "Wood - Chip Board" and click the OK button of the dialog to return to the "Edit Layer" dialog. Now you will see the properties of chipboard in the dialog: εr = 2.4 and σ = 0.04S/m. Close this dialog to return to the penetrable surface dialog. Make sure that the new material and its properties show up in the table. Close this dialog, too, and return to the project workspace.
Now, run a new SBR analysis of your propagation scene and visualize its received power coverage map. You can see from the figure below that the power levels of the receivers located inside the building called "Box_3" have dropped significantly compared to the previous case. This is due to the increased value of the wall's conductivity.
Changing the Polarization of the Transmitter Antenna
EM.Terrano's default transmitter features a vertical half-wave dipole radiator. In the last part of this tutorial lesson, you are going to rotate the radiation pattern of the default dipole to turn it into a horizontally polarized antenna. The table below shows the radiation patterns of vertical and horizontal dipole antennas.
|Rotation Order||Rotation Angle||Rotation Axes||Radiation Pattern|
Open the property dialog of your transmitter and select the radio button labeled "User Defined Antenna". In the box next to the Import Pattern button, you see the path to the default radiation pattern data file. This file is called "DPL_STD.RAD" and is located in the "Models" folder under the documents folder. You don't have to change the file path. In the Rotation Angles section, enter (0°, 90°, 0°) for the rotation angles with respect to the X, Y and Z-axes. Close the transmitter dialog and return to the project workspace.
Run a new SBR analysis of your propagation scene with the horizontal dipole transmitter. Visualize the received power coverage map as shown in the figure below. Note that the receivers close to the transmitter and located along the X-axis have experienced a significant drop in their power levels due to the null of the horizontal dipole's radiation pattern along that direction.