Carrier-to-Noise Ratio in the LEO, MEO, and GEO Zones

STK Premium (Air) and STK Premium (Space) or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following capabilities of the Ansys Systems Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • STK SatPro
  • Aviator
  • Communications
  • Analysis Workbench
  • Coverage
  • Volumetric Analysis

Problem statement

Engineers and analysts require an efficient way to create constellations of satellites with similar payloads. They may also need to determine if receivers on those satellites will sustain interference from other communication devices. You want to evaluate an aircraft's communications link with a constellation of satellites in low Earth orbit (LEO) as the aircraft flies a search pattern. The testbed aircraft is outfitted with a phased array communication antenna. You need to evaluate the additional RF energy which may interfere with other satellites in LEO, medium Earth orbit (MEO), and geostationary Earth orbit (GEO).

Solution

Use the STK software and the SatPro capability's Walker Tool to create a constellation of satellites. Next, create an Aircraft object that flies a search pattern in a designated area of interest using the STK software's Aviator capability. You will use a CommSystem object, part of the Communications capability, to determine possible communication interference with the LEO satellites and evaluate the carrier-to-noise ratio (C/N). Finally, you will use the Analysis Workbench and Volumetric Analysis capabilities to visualize potential radio frequency interference in the LEO, MEO and GEO volume of space.

What you will learn

Upon completion of this lesson, you will understand the following:

  • The Walker Tool
  • Aviator Area Target Search patterns
  • The CommSystem object
  • The Spatial Analysis tool
  • The Volumetric object

Creating a new scenario

You will create a new scenario with a run time of five hours.

  1. Launch the STK application ().
  2. Click Create a Scenario () in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name Volumetrics_CN
    Start 15 Mar 2022 16:00:00.000 UTCG
    Stop + 5 hrs
  4. Click OK when you finish.
  5. Click Save () once the scenario loads. A folder with the same name as your scenario is created for you.
  6. Verify the scenario name and location.
  7. Click Save.

Save () often!

Creating a LEO constellation

You will use a Walker constellation to model the constellation of LEO satellites. Each satellite will have a hemispherical nadir pointing antenna. In order to define the walker constellation, you first need to create a "seed" satellite to define the general orbital parameters.

Understanding Walker constellations

The Walker Tool, available as part of the STK Software's SatPro capability, makes it easy to generate a Walker constellation using the Two Body, J2, J4, or SGP4 orbit propagators. A Walker constellation consists of a group of satellites (t) that have the same period and inclination. The pattern of the constellation consists of evenly spaced satellites (s) in each of the orbital planes (p) specified so that t=sp. The ascending nodes of the orbital planes are also evenly spaced over a range of right ascensions (RAAN).

The way in which spacing between the ascending nodes that define the orbital planes is calculated depends on the type of Walker constellation you choose. In addition to specifying the number of satellites in each plane, you must also specify the location of the first satellite in each plane relative to the first satellite in adjacent planes. The way to specify the position of the first satellite depends on the type of Walker constellation you choose.

Type Description
Delta Delta configurations have orbit planes distributed evenly over a span of 360 degrees in right ascension. Requires an integer value of f for inter-plane phasing.
Star Star configurations have orbit planes distributed over a span of 180 degrees. Requires an integer value of f for inter-plane phasing.
Custom A Custom configuration allows for explicit input of the span over which ascending nodes should be distributed and allows for the explicit specification of inter-plane phasing in terms of a true anomaly offset.

Creating a seed satellite

First, define a satellite with the characteristics and orbit you need, then, use the Walker Tool to create a Walker constellation. The original satellite that is used to create the Walker constellation is referred to as the "seed" satellite, while the satellites generated using the Walker Tool are referred to as Child satellites. Use the Orbit Wizard to create the "seed" satellite from which the other satellites will be derived.

  1. Select Satellite () in the Insert STK Objects tool ().
  2. Select the Orbit Wizard () method.
  3. Click Insert. . ..
  4. Set the following options in the Orbit Wizard:
    5. Option Value
    Type Repeating Ground Trace
    Satellite LEO_Sat
    Approximate Altitude 800 km
    Color White
  5. Click OK to confirm your selections and to insert the seed satellite.

Modeling the LEO satellite's receiver

Insert a Receiver object which will function as the receiver on the LEO satellite and all of its children. You will use a Complex Receiver model. A Complex Receiver Model enables you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Insert a Receiver () object using the Define Properties () method.
  2. Select LEO_Sat () in the Select Object dialog box.
  3. Click OK.
  4. Select the Basic - Definition page.
  5. Click the Receiver Model Component Selector ().
  6. Select Complex Receiver Model () in the Select Component dialog box.
  7. Click OK to confirm your selection and to close the Select Component dialog box.

Selecting the Receiver's antenna model

Use the Basic Definition page for a receiver, transmitter, radar, or antenna object to select an antenna model type from the Component Browser.

  1. Select the Antenna tab.
  2. Click the Antenna Models Component Selector ().
  3. Select Hemispherical ().

    4. A Hemispherical antenna type provides a built-in model antenna gain pattern covering half of the hemisphere along the boresight.

  4. Click OK to confirm your selection and to close the Select Component dialog box.
  5. Click Apply to save your changes and to keep the Properties Browser open.

Visualizing the antenna pattern

Display the shape and volume of the antenna pattern using the receiver's 3D Graphics – Attributes page.

  1. Select the 3D Graphics – Attributes page.
  2. Select the Show Volume check box.
  3. Click OK.
  4. Right-click on Receiver1 () in the Object Browser.
  5. Select Rename the shortcut menu.
  6. Rename Receiver1 () LEO_Rx.
  7. Right-click on LEO_Sat () in the Object Browser.
  8. Select Zoom To in the shortcut menu.
  9. Bring the 3D Graphics window to the front.
  10. Use your mouse to get a good view of the satellite and the antenna pattern.

Hemispherical Antenna Pattern

Creating a Walker constellation

Using the seed satellite, create a constellation with orbital characteristics that provide global coverage. You will design a constellation that has at least one satellite in view of the aircraft at all times.

  1. Right-click on LEO_Sat () in the Object Browser.
  2. Select Satellite in the shortcut menu.
  3. Select Walker... in the Satellite submenu.
  4. Enter the following in the Walker Tool:
    5. Option Value
    Type Delta
    Number of Sats per Plane 10
    Number of Planes 10
    Color by Plane Cleared
  5. Click Create / Modify Walker to insert the Walker constellation.
  6. Click Closeto close the Walker Tool.

If the seed satellite contains child objects such as Receiver objects, the sub-objects are also created for each of the child satellites.

Clearing the seed satellite

When a Walker constellation is created, each child has the same base name as the seed satellite plus two numbers. The first number identifies the plane in which the satellite resides and the second identifies the satellite's position in the plane. In this case, you've created a Walker constellation with two planes and ten satellites per plane, LEO_Sat0102 is the second satellite in the first plane. If you keep the seed satellite in the scenario, two identically configured satellites (the seed satellite and the first satellite in the first plane) will be considered in your analysis. To prevent duplicate analysis, remove the seed satellite.

  1. Save () your scenario.

    2. When you save the scenario, all objects in the scenario are also saved. It is important that you save the scenario before you remove LEO_Sat in case you need to reload it later for further analysis.

  2. Select LEO_Sat () in the Object Browser.
  3. Click Delete ().
  4. Click Delete to confirm your deletion when the Delete Object dialog box opens.

Viewing the LEO satellite constellation

View your Walker constellation in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Click Home View () in the 3D Graphics window toolbar.
  3. Use your mouse to turn the Earth in order to view the constellation of LEO satellites.

LEO Constellation

Creating the test area

Use an Area Target object to create the training area in which the test aircraft will fly a standard search pattern.

  1. Insert an Area Target () object using the Define Properties () method.
  2. Select the Basic - Boundary page
  3. Click Add four times in the Points panel to add four points to the Points table.

    4. The Points table displays a summary of the latitude and longitude values for each perimeter point.

  4. Set the following values for the perimeter points in the order shown:
    5. Latitude Longitude
    34 deg -121 deg
    34 deg -119 deg
    32 deg -119 deg
    32 deg -121 deg
  5. Click Apply.
  6. Select the 2D Graphics - Attributes page.
  7. Clear the Inherit from Scenario check box in the Inheritable Settings panel.
  8. Clear the Show Label and Show Centroid check boxes.
  9. Click OK.
  10. Rename AreaTarget1 () Test_Area.

Creating the test aircraft

Create and define your aircraft, which is serving as a communications testbed. It is equipped with a phased array antenna and will fly a search pattern inside of a designated test area.

Inserting a new Aircraft object

Use Aviator to propagate the aircraft. With Aviator, the aircraft's route is modeled by a sequence of curves parameterized by well-known performance characteristics of aircraft, including cruise airspeed, climb rate, roll rate, and bank angle.

  1. Insert an Aircraft object () using the Insert Default () method.
  2. Click Insert. . ..
  3. Open Aircraft1's () Properties ().
  4. Ensure the Basic - Route page is selected
  5. Select Aviator in the Propagator drop-down list.

Selecting the aircraft model

You are using a twin-engine turboprop aircraft for the test. Select a predefined aircraft model to define the physical characteristics of the test aircraft, its configuration, and its mode of flight.

  1. Click Select Aircraft () in the Initial Aircraft Setup toolbar.
  2. Select Basic Turboprop () in the User Aircraft Models () list when the Select Aircraft dialog box opens.
  3. Click OK to confirm your selection and to close the Select Aircraft dialog box.
  4. Click Apply.
  5. Rename Aircraft1 () TestAircraft.

Inserting an Area Target site

You can use an Area Target as a site for an Aviator procedure. The site defines the location (excluding altitude) of the procedure and the types of procedures that are available to select. The exact relationship between the site location and the procedure is dependent on the specific procedure.

  1. Right-click on Phase 1 () in the Mission List.
  2. Select Insert First Procedure for Phase ... () in the shortcut menu.
  3. Select STK Area Target () in the Select Site Type list.
  4. Click Next >.

Configuring an Area Target Search procedure

An Area Target Search procedure conducts a search pattern flight — comprised of raster parallel lines — within the selected Area Target site.

  1. Select AreaTargetSearch () in the Select Procedure Type list.
  2. Clear the Use Aircraft Default Cruise Altitude check box in the Altidude panel.
  3. Enter 10000 ft in the Altitude field.
  4. Set the following options in the Search Options panel:
    5. Option Value
    Max Separation 10 nm
    Course Mode Override
    Centroid True Course 180 deg

    The search pattern is based on the course defined for the area target's centroid. The STK software's Aviator capability will fill the search area with parallel flight lines derived from the centroid's course, and the point of entry to the search pattern is defined relative to that course.

  5. Change Turn Factor to 2 in the Enroute Options panel.
  6. Ensure Max Range Airspeed is selected in the Enroute Cruise Airspeed panel.

    7. This is a variable airspeed that maximizes the distance the aircraft can fly.

  7. Click Finish.
  8. Click OK.
  9. Click Optimize STK for Aviator when the Flight Path Warning window appears.
  10. Click OK.

Viewing the search pattern in the 3D Graphics window

Review your changes in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Test_Area () in the Object Browser.
  3. Select Zoom To in the shortcut menu.
  4. Click Orient North ().
  5. Zoom out until you can see the full extent of the test area and the aircraft's flight route.

Aircraft Search Pattern

Building the aircraft's transmitter

Define the transmitter you are using for the tests. You will use a Complex Transmitter Model, which allows you to select among a variety of analytical and realistic antenna models, and to define the characteristics of the selected antenna type.

  1. Insert a Transmitter () object using the Define Properties () method.
  2. Select TestAircraft () in the Select Object dialog box.
  3. Click OK.
  4. Select the Basic - Definition page.
  5. Select the Transmitter Model Component Selector ().
  6. Select the Complex Transmitter Model () in the Select Component dialog box.
  7. Click OK.
  8. Select the Model Specs tab.
  9. Set Power to 40 dBW.
  10. Click Apply.

Modeling the phased array transmitter antenna

Select a Phased Array antenna model from the Component Browser and define its characteristics. A Phased Array antenna model consists of many radiating elements, each of which is modeled as an isotropic pattern.

  1. Select the Antenna tab.
  2. Ensure the Model Specs sub-tab is selected.
  3. Select the Antenna Model Component Selector ().
  4. Select Phased Array () in the Select Component dialog box.
  5. Click OK.
  6. Ensure the Element configuration sub-sub tab is selected.

    7. The Element Configuration tab enables you to define the physical aspects of the antenna elements.

  7. Enter 9 in the X field in the Number of Elements panel.
  8. Enter 9 in the Y field in the Number of Elements panel.

Updating the beam target

Use the Beam Direction Provider sub-sub-tab to select where the antenna points its beam. By modifying the excitation (amplitude and phase) of each element differently, a phased array antenna can electronically steer its maximum gain toward a particular direction or main radiation axis.

  1. Select the Beam Direction Provider sub-sub-tab.
  2. Select the Enabled check box in the Beam Steering panel.
  3. Click Clear All Filters in the Selection Filter panel.
  4. Select the Satellite () check box in the Selection Filter panel.
  5. Move () all of the satellites to the beam target list.
  6. Click Apply.

Updating the antenna's orientation

The STK software provides methods to specify the orientation of the antenna coordinate frame relative to the coordinate frame of the parent object. The antenna uses a spherical Az/El coordinate system. This method specifies the location of the antenna boresight in relation to the azimuth and elevation in the local coordinate frame of the parent object, in this case, the test aircraft.

  1. Select the Orientation sub-tab.
  2. Set the Elevation to -90 deg.

    3. An antenna on a vehicle has a default alignment in which the antenna boresight looks down the +Z axis of the vehicle. The default vehicle attitude ("Nadir aligned with ECI velocity vector constraint" for satellites, and "Nadir aligned with ECF velocity vector constraint" for other vehicles) results in the antenna boresight pointing straight down toward the center of the Earth, so an elevation of -90 degrees points the antenna boresight straight up, not down.

  3. Set Z to -1.9 ft in the Position Offset panel.

    4. This will place the antenna on top of the aircraft's fuselage.

  4. Click Apply.

Visualizing the antenna pattern

You want to visualize the antenna pattern as a 3D volume.

  1. Select the 3D Graphics - Attributes page.
  2. Set the following options in the Volume Graphics panel:
    3. Option Value
    Show Volume Selected
    Gain Scale (per dB) 0.0005 km
    Minimum Displayed Gain -20 dB
  3. Select the Set azimuth and elevation resolution together check box in the Pattern panel.
  4. Click Apply.

Displaying the boresight vector

The boresight vector is a unit vector along the Body Z axis. The Vector is fixed by its components in reference axes.

  1. Select the 3D Graphics - Vector page.
  2. Select the Show check box for the Boresight Vector option.
  3. Click OK.
  4. Rename Transmitter1 () to TestAircraft_Tx.
  5. Right-click on TestAircraft () in the Object Browser.
  6. Select Zoom To in the shortcut menu.
  7. Bring the 3D Graphics window to the front.

Antenna Pattern and Boresight vector

Plotting C/N along the flight route

There are a couple of ways to approach this problem. Mission planners could use a Chain object and create a link between the test aircraft's transmitter and whatever LEO receivers are in view. Or they could employ a CommSystem object and direct the phased array's main lobe gain towards the LEO satellite that is has the best overhead elevation angle when multiple satellites are in view. Mission planners have decided on the latter.

Organizing the communication system

The STK software's Communications capability provides a CommSystem object that allows you to model dynamically configured communications links between constellations of transmitters and receivers. CommSystems are particularly useful for modeling low and medium Earth orbiting (LEO and MEO) satellite systems. To set up a CommSystem object, you must first organize the relevant communication assets:

  • the transmitter(s) in the communications link of interest
  • the receiver(s) in the communications link of interest

You can organize the communications assets using Constellation objects.

  1. Insert a Constellation () object into the scenario using the Insert Default () method.
  2. Rename Constellation1 () object Transmitter.
  3. Insert another Constellation () object into the scenario using the Insert Default () method.
  4. Rename Constellation2 () object Receivers.

Creating the Transmitter constellation

Add the test aircraft's transmitter to the Transmitter constellation.

  1. Open Transmitter’s () Properties ().
  2. Select the Basic - Definition page.
  3. Select TestAircraft_Tx () in the Available Objects list.
  4. Move () TestAircraft_Tx () to the Assigned Objects list.
  5. Click OK.

Creating the Receivers constellation

Add the satellites' receivers to the Receivers constellation.

  1. Open Receivers' () Properties ().
  2. Select the Basic - Definition page.
  3. Select the Receiver () check box in the Selection Filter list.
  4. Move () all the receivers to the Assigned Objects list.
  5. Click OK.

Building the communications system

Select the constellations to carry out the transmit and receive functions in the system.

  1. Insert a CommSystem () object using the Insert Default () method.

    2. If the CommSystem () object does not appear in the Insert STK Objects tool, click Edit Preferences... and select the Show check box to display the object in the Insert STK Objects tool.

  2. Open CommSystem1’s () Properties ().
  3. Select the Basic - Transmit page.
  4. Select Transmitter () in the Available Constellations list.
  5. Move () Transmitter () from the Available Constellations list to the Assigned Constellation list.
  6. Select the Basic - Receive page.
  7. Select Receivers () in the Available Constellations list.
  8. Move () Receivers () from the Available Constellations list to the Assigned Constellation list.

Constraining the communications links

Complex communication systems may present many potential links for a given receiver or transmitter. You must define the criteria for determining which transmitter will communicate with which receiver.

  1. Select the Basic - Link Definition page.
  2. Select the Transmit option in the Constraining Constellations panel.

    3. Constraining Constellations will generally, but not always, comprise the objects closest to the Earth. Only one link will be established for each object contained within the constraining constellations.

  3. Leave the Link Selection Criteria set at Minimum Range.

    4. Minimum Range selects the non-constraining objects (the satellite receivers) with the minimum distance to the constraining object (the test aircraft’s transmitter). Basically, you're forcing the phased array antenna to talk to the nearest satellite.

  4. Click OK.

Computing the CommSystem and plotting C/N

After defining your CommSystem, set the CommSystem object to process link information. Because of the dynamic nature of these more complex systems, the CommSystem performs a more traditional analysis by implementing a simulation in which time is advanced over the specified interval at fixed time steps and in which the links are analyzed at each step. The resulting data are available after the simulation is complete for reporting or graphing purposes.

  1. Right-click on CommSystem1 () in the Object Browser.
  2. Select CommSystem in the shortcut menu.
  3. Select Compute Data in the CommSystem submenu.

    4. When you select Compute Data, a two-phase process begins to generate the desired information. The first phase analyzes the visibility of the transmitters, receivers, and interference sources (if available) to each other to determine when they are accessible. Access calculations take into account any of the normal access constraints that may be applied to each of the objects. The second phase steps through the desired CommSystem interval, calculating the link performance. During each of the phases, a Progress window appears. The first phase of calculations is completed rather quickly but the second phase can be lengthy, depending on the complexity of the CommSystem. After link performance and interference are calculated, the desired links, interference sources, and the primary interferer appear in the 2D and 3D Graphics windows.

Be patient! Due to the amount of receivers in the scenario, the computation can take a few minutes.

Generating a Carrier to Noise vs. Time graph

The STK software's Communications capability provides report and graph elements for CommSystems. Use the predefined Carrier to Noise vs Time graph to view C/N over the course of the mission.

  1. Right-click on CommSystem1 () in the Object Browser.
  2. Select Report & Graph Manager... ().
  3. Select the Carrier to Noise vs Time () graph in the Installed Styles list.
  4. Click Generate....
  5. Click Show Step Value when the graph opens.
  6. Change Step to 1 sec.
  7. Click Refresh (F5) () in the graph toolbar.

    8. C/N Over Time

    You can see that there are several instances where C/N is affected.

  8. Close the graph and the Report and Graph manager when you are finished.

Analyzing the RF output throughout MEO with a Volumetric object

You would like to ensure that the RF energy used for your communications link doesn’t interfere with other satellite communications beyond MEO to GEO. In order to evaluate C/N across the MEO, you can define a scalar calculation using the Analysis Workbench capability to a grid template object, and have that grid template object move to all the grid point locations defined in a Volumetric object, which is part of the STK software's Volumetric Analysis capability.

Creating the Volumetric object

A Volumetric object defines a three-dimensional grid of points using various coordinate definitions, with respect to various reference coordinate systems from the Vector Geometry tool. It also defines the conditions and calculations that depend on locations in 3D space and evaluates these conditions and calculations across grid points.

  1. Insert a Volumetric () object using the Insert Default () method.
  2. Rename Volumetric1 () to Vol_CN.

Creating a new Volume Grid component

Select a Volume Grid component from Analysis Workbench.

  1. Open Vol_CN's () Properties ().
  2. Select the Basic - Definition page.
  3. Click the Volume Grid ellipsis ().
  4. Click Create new Volumetric Grid () when the Select Volume Grid for CN_Vol dialog box opens.
  5. Click Select... next to the Type field.
  6. Select Cartographic in the Select Component Type list when the Select Component Type dialog box opens.

    7. A Cartographic grid uses latitude, longitude and altitude based on the central body reference ellipsoid.

  7. Click OK to confirm your selection and to close the Select Component Type dialog box.
  8. Enter MEO_West in the Name field.

Setting and defining the volume grid values

Add the coordinate steps for your volumetric object.

  1. Click Set Grid Values....
  2. Set the following options in the Longitude panel when the Grid Values dialog box opens:
    3. Option Value
    Minimum -180 deg
    Maximum 0 deg
    Number of Steps 10
  3. Set the following options in the Altitude panel:
    4. Option Value
    Minimum 2000 km
    Maximum 36000 km
    Number of Steps 5
  1. Click OK to close the Grid Values dialog box.
  2. Click OK to close the Add Volumetric Component dialog box.
  3. Select MEO_West in the Volume Grids for: Earth list.
  4. Click OK.
  5. Click Apply.

Viewing the volume grid

View your changes in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front
  2. Click Home View () in the 3D Graphics window toolbar.
  3. Use your mouse to view the Cartographic Grid (MEO_West).

MEO_West Cartographic Grid

Changing the view

Use the Volumetric 3D Graphics Grid page to define the 3D Graphics properties of the Volumetric grid.

  1. Return to Vol_CN's () Properties ().
  2. Select the 3D Graphics - Grid page.
  3. Change Size to 2 in the Show grid points field.
  4. Clear the Show grid lines check box.
  5. Click Apply.
  6. Return to the 3D Graphics window to view your changes.

MEO_West Grid Points Only

Defining the volumetric grid

You can use one of the satellites' receivers as the volumetric grid template object. In order to do this, you will need to compute an access from the aircraft transmitter to that receiver so that the scalar calculation for C/N will exist.

  1. Right-click on TestAircraft_Tx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Expand () LEO_Sat0101 () in the Associated Objects list when the Access Tool opens.
  4. Select LEO_Rx1().
  5. Click .
  6. Click Close to close the Access tool.

Using the Spatial Analysis Tool

Use the Spatial Analysis Tool to create calculations and conditions that depend on locations in 3D space which are, in turn, provided by user-definable volume grids.

You have computed access from the test aircraft’s transmitter to the LEO satellite receiver. The STK software's Analysis Workbench capability has automatically created scalar calculations for all the available communications calculations, including C/N. Next, create a spatial calculation that will move the template object to each point in the volumetric grid and compute C/N at those locations.

  1. Right-click on LEO_Sat0101 () in the Object Browser.
  2. Select Analysis Workbench... () in the shortcut menu.
  3. Select the Spatial Analysis tab when Analysis Workbench opens.

Creating a new spatial calculation

A spatial calculation is a calculation that depends on both time and location.

  1. Click Create new Spatial Calculation ().
  2. Ensure that the Type is set to Scalar At Location.

    3. This spatial calculation is defined by placing its parent object at various locations on the grid and evaluating the selected (non-spatial) Scalar Calculation from the Calculation tool.

  3. Enter CN in the Name field.
  4. Click the Scalar ellipsis ().
  5. Select Aircraft-TestAircraft-TransmitterTestAircraft_Tx-To-Satellite-LEO_Sat0101-Receiver-LEO_Rx1 () in the objects list when the Select Reference Scalar Calculation dialog box opens.
  6. Expand () CommLinkInformation () in the Scalar Calculations for: Aircraft-TestAircraft-Transmitter-TestAircraft_Tx-To-Satellite-LEO_Sat0101-Receiver-LEO_Rx1 list.
  7. Select C/N ().
  8. Click OK to close the Select Reference Scalar Calculation dialog box.
  9. Click OK to close the Add Spatial Analysis Component dialog box.
  10. Click Close to close the Analysis Workbench.

Updating the volumetric object to use the C/N spatial calculation

Now that you have created the C/N spatial calculation, configure the Volumetric object to use that spatial calculation.

  1. Return to Vol_CN's () Properties ().
  2. Select the Basic - Definition page.
  3. Select the Spatial Calculation check box.
  4. Click the Spatial Calculation ellipsis ().
  5. Select LEO_Sat0101 () in the object list when the Select Spatial Calculation for Vol_CN dialog box opens.
  6. Select CN () in the Spatial Calculations for: LEO_Sat0101 list.
  7. Click OK to close the Select Spatial Calculation for Vol_CN dialog box.
  8. Click Apply.

Computing the volumetric analysis

Volumetric Analysis is likely to be more computationally expensive that 2D analysis because extending grids to three dimensions can greatly increase the number of grid points.

  1. Right-click on Vol_CN () in the Object Browser.
  2. Select Volumetric in the shortcut menu.
  3. Click Compute in Parallel in the Volumetric submenu.

Be patient! Due to the amount of receivers and grid points in the scenario, the computation can take a few minutes.

Configuring the volumetric basic interval

To animate the scenario, the Volumetric Analysis capability will need to recompute the data at every time step. In order to compute all of the data beforehand to animate smoothly, adjust the Interval to use the At times at step size option.

  1. Return to Vol_CN's () Properties ().
  2. Select the Basic - Interval page.
  3. Select the At times at step size check box in the Evaluation of Spatial Calculation panel.
  4. Enter 5 min in the At times at step size field.

    5. On your own, you can adjust this value to what works for you. Any changes you make will be applied to the spatial calculation limits in the 3D Graphics - Volume page. Therefore, you may want to redo your fill levels.

  5. Click Apply.

Be patient. This could take a few minutes.

Configuring volumetric graphics

Spatial Calculation Levels represent straight line distances from the parent object. You can set them on the Volumetric 3D Graphics Volume page.

  1. Select the 3D Graphics - Volume page.
  2. Select the Spatial Calculation Levels option.

    3. When the Spatial Calculation Levels option is selected, the minimum and maximum limits of the spatial calculation can be seen at the top of the page in the Limits panel. Your values may be different. The following image is only an example.

    Spatial Calculation Limits

  3. Click Insert Evenly Spaced Values....
  4. Set the following options in the Insert Evenly Spaced Values dialog box:
    5. Option Value
    Units dB
    Start Value -10
    Stop Value Round down to the highest Max integer (in the above example, 7 dB)
    Step Size 3

    The start value could be any value you choose; in this instance, it's an arbitrary value. For this scenario you're saying a C/N of -10 dB or higher could create interference.

  5. Click Create Values.
  6. Click Apply.

Setting the 3D Graphics legends

Use the Volumetric 3D Graphics Legends page to adjust the legend display in your 3D Graphics window.

  1. Select the 3D Graphics – Legends page.
  2. Select the Show Legend check box.
  3. Set the following options in the Text Options panel:
    4. Option Value
    Title C/N (dB)
    Number Of Decimal Digits 0
  4. Set the following options in the Range Color Options panel:
    5. Option Value
    Max Color Squares per Row 40
    Color Square Width (pixels) 50
  5. Click OK.

Viewing C/N in the 3D volume of space

View your dynamic volumetric object in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Reset () your scenario.
  3. Click Normal Animation Mode () in the Animation toolbar.
  4. Decrease Time Step () to 30 seconds in the Animation Toolbar.
  5. Click the Home View ().
  6. Zoom out so you can see the whole airspace.
  7. Start () the animation.

C/N 3D Graphics

You can see that C/N changes every five minutes.

Saving your work

Close out the scenario and save your work.

  1. Reset () the scenario when you are finished.
  2. Close any reports or tools that are still open.
  3. Save () your work.

Summary

You started by creating a constellation of LEO satellites using Walker tool; each satellite had receiver. Next, you designed an Aircraft object that flew a search pattern in a designated area of interest using the Aviator propagator. You utilized the CommSystem object to determine possible communication interference with the LEO satellites. Finally you will created a Volumetric object using the Spatial Analysis tool to create a custom grid to visualize potential radio frequency interference in the LEO, MEO and GEO volume of space.

On your own

Throughout the lesson, hyperlinks were provided that pointed to in depth information. Now's a good time to go back through this tutorial and view that information. Create your own satellite constellation with receivers and a static ground site and transmitter to evaluate interference and apply it to your own custom grid.