Electromagnetic Spectrum Analysis

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.

Additional installation - Spectrum Analyzer plugin. The Spectrum Analyzer plugin comes with the STK install. During the installation process, you are to choose desired plugins. Choose Spectrum Analyzer. Another way to get the Spectrum Analyzer is to go to http://support.agi.com/downloads, select the Other tab, and choose your version of STK from the STK UI Plugins table row. Note that you need to log in using your AGI web account credentials to access the Sofware Downloads site. If you are experiencing problems getting and installing Spectrum Analyzer, simply contact Support at 1-800-924-7244 or 610-981-8888.

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 STK Capabilities:

  • STK Pro
  • STK SatPro
  • Communications

Problem Statement

A constellation of low Earth orbit (LEO) satellites is being proposed that will transmit data within the Ku band. Many ships operate in this portion of the electromagnetic spectrum. The Global Shipping Conglomeration is concerned that the LEO satellites could interfere with satellite communications globally.

Solution

Use STK Pro and STK's SatPro and Communications capabilities to model and analyze this system. Build an STK scenario that simulates a portion of the proposed constellation of LEO satellites. Model a ship located off the coast of Southern California. Determine a Link Budget between the ship and a geosynchronous (GEO) satellite. During a limited period of time, determine if any of the satellites interrupt data transfer between the GEO satellite and the ship. Use the Spectrum Analyzer to view the spectrum utilization and visualize potential interference on the communication link.

Throughout this tutorial, unless otherwise specified, use default settings.

Video Guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Create a New Scenario

Create a new scenario with a run time of two (2) hours.

  1. Click the Create a Scenario () button.
  2. Enter the following in the New Scenario Wizard:
    3. Option Value
    Name: STK_SpectrumAnalyzer
    Start: 1 Jun 2018 19:00:00.000 UTCG
    Stop: + 2 hrs
  3. When you finish, click OK .
  4. When the scenario loads, click Save (). A folder with the same name as your scenario is created for you.
  5. Verify the scenario name and location and click Save .

Save Often!

Disable Terrain Server

  1. Open the STK_SpectrumAnalyzer () properties ().
  2. Browse to the Basic – Terrain page.
  3. Clear the Use terrain server for analysis checkbox.
  4. Click OK .

Geosynchronous Satellite

Insert a Satellite () object which will function as the communications satellite.

  1. Insert a Satellite object () using the Orbit Wizard () method.
  2. Make the following changes:
    3. Option Value
    Type: Geosynchronous
    Satellite Name: GEO_Sat
  3. Keep the other default settings.
  4. Click OK .

GEO Satellite Transmitter

Insert a Transmitter () object which will function as the transmitter on the GEO satellite.

  1. Insert a Transmitter () object using the Define Properties () method.
  2. On the Select Object window, select GEO_Sat () and click OK .
  3. On the Basic - Definition page, click the ... button to change the Type: field to Complex Transmitter Model.
  4. Click Apply .

Parabolic Antenna

The GEO Satellite is transmitting with a parabolic antenna.

  1. On the Basic - Definition page, select the Antenna tab.
  2. Make the following changes:
    3. Option Value
    Type: Parabolic
    Diameter: 2 m
  3. Select the Orientation sub-tab and make the following changes:
    4. Option Value
    Azimuth: 244.0529 deg
    Elevation: 83.92558 deg
  4. Click Apply .

Transmitter Modulation

The Power Spectral Density (PSD) option allows STK's Communications capability to model the actual spectral shape of the transmitted signal based on the modulation, data rate, etc. The number of nulls will automatically set the signal's bandwidth.

  1. On the Basic - Definition page, select the Modulator tab.
  2. Select the Use Signal PSD check box.
  3. Set the Number of Spectrum Nulls: field to 3.
  4. Click OK .
  5. Rename the Transmitter () object "GEO_Tx".

Test Ship

Insert a Ship () object which will function as the test location for the satellite communications reception

  1. Insert a Ship object () using the Define Properties () method.
  2. On the Basic - Route page, change the Route Calculation Method: field to Specify Time.
  3. Set the Altitude Reference - Reference field to WGS84.
  4. Click Insert Point and make the following changes:
    5. Option Value
    Latitude: 33.65 deg
    Longitude: -119.56 deg
  5. Click Insert Point again.
  6. Add two (2) hours to point number two's time (ex. 1 Jun 2018 21:00:00.000 UTCG).
  7. Click Apply .

Add Vector For Situational Awareness

Add a vector to the ship which targets the GEO satellite.

  1. Open the ship's 3D Graphics - Vector page.
  2. Click Add... to open the Add Components window.
  3. Select the Ship object on the left.
  4. Expand the To Vectors folder on the right.
  5. Select the GEO_Sat.
  6. Click OK .
  7. In the Common Options - Component Size section, set Scale: to 2.2.
  8. Click OK .

View the ship

Let's look at the ship and the vector.

  1. Rename the Ship () object "Ship".
  2. Bring the 3D Graphics window to the front.
  3. In the Object Browser, right-click on Ship and select Zoom To.
  4. Use your mouse buttons to get a good look at the ship and the vector which points to the GEO satellite.

Ship and Vector

GEO Satellite Antenna Orientation (Parabolic Antenna Boresight)

The GEO satellite antenna's boresight is located in Southern California (antenna orientation). The ship is approximately 67 kilometers away from this location at a bearing of 219 degrees. You can see this on the 2D Graphics window.

  1. Bring the 2D Graphics window to the front.
  2. Open the 2D Graphics window's properties ().
  3. On the Imagery page, clear the Background Image - Show check box.
  4. Open the Details page.
  5. In the Map Details field, click to enable the following options:
    • RWDB2_Coastlines (enabled by default)
    • RWDB2_International_Borders
    • RWDB2_Islands
    • RQDB2_Provincial_Borders.
  6. Click OK .
  7. Zoom in to the map so that you can see the Ship object and a small (X) on the California coast which pinpoints the antenna boresight.

Antenna Boresight

Ship's Receiver

Insert a Receiver () object which will function as the ship's receiver.

  1. Insert a Receiver () object using the Define Properties () method.
  2. On the Select Object window, select Ship () and click OK .
  3. On the Basic - Definition page, click the ... button to change the Type: field to Complex Receiver Model.
  4. Clear the Auto Track check box, but keep the default frequency (14.5 GHz).
  5. Click Apply .

Receiver's Antenna

The ship has a phased array antenna and will dedicate 19 elements for the exercise.

  1. On the Basic - Definition page, select the Antenna tab.

    2. The Antenna tab is further split up into three tabs.

  2. On the Model Specs tab, set the Type: field to Phased Array.

    3. The Model Specs tab is even further split into four tabs.

  3. Select the Element Configuration tab.
  4. Set the following values:
    5. Option Value
    Number of Elements - X: 5
    Number of Elements - Y: 5
  5. Click Apply .

Target the geosynchronous satellite

The phased array antenna elements will track the GEO satellite.

  1. Select the Beam Direction Provider tab.

    2. This tab is next to the Element Configuration tab.

  2. In the Beam Steering field, select the Enabled check box.
  3. Select GEO_Sat in the Available Objects list and move () it to the Assigned Objects list.
  4. Click Apply .
  5. Select the Filter tab.

    6. This tab is on the same level as the Antenna tab.

  6. In the Receiver Bandwidth section, clear the Auto Scale check box and set the Bandwidth: to 96 MHz.
  7. Click Apply .

Display the volume graphics

Volume graphics allow you to display the shape and gain levels of antenna beams.

  1. Select the 3D Graphics - Attributes page.
  2. Make the following changes to the Volume Graphics section:
    3. Option Value
    Show Volume On
    Minimum Displayed Gain: -10 dB
  3. Make the following changes to the Pattern section:
    4. Option Value
    Set azimuth and elevation resolution together On
    Azimuth - Resolution: 1 deg
  4. Click OK .
  5. Rename the Receiver () object "Ship_Rx".
  6. Bring the 3D Graphics window to the front.
  7. In the Object Browser, right-click on Ship and select Zoom To.
  8. Use your mouse buttons to get a good look at the ship and the phased array antenna pattern.

Phased Array Antenna Pattern

Link Budget

A Link Budget Report between the ship and the GEO satellite is simple to accomplish in STK.

  1. Right-click on Ship_Rx () and select Access () to open the Access Tool.
  2. In the list, expand () GEO_Sat ().
  3. Select GEO_Tx ().
  4. Click .
  5. In the Reports section, click Link Budget... .
  6. Scroll to the right of the report and note the Eb/No (dB)values. Eb/No (dB) is what we'll focus on throughout the tutorial.
  7. Close the report and the Access Tool.

Walker constellations

The Walker Tool makes it easy to generate a Walker constellation using the Two Body, J2, J4, or SGP4 orbit propagators. First, define a satellite with the characteristics and orbit you need and then open the Walker tool by highlighting the satellite in the Object Browser and selecting Walker... from the Satellite menu.

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.

Create a Seed Satellite

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 children. Use the Orbit Wizard to create the “seed” satellite from which the other satellites will be derived.

  1. Insert a Satellite () object using the Orbit Wizard () method.
  2. On the Orbit Wizard window, set the following:
    3. Option Value
    Type: Sun Synchronous
    Satellite Name: LEO_Sat
  3. Click OK .

Sensor field of view for situational awareness

Use a Sensor object’s field of view which will encompass eighteen (18) antenna beams for a particular LEO satellite. This field of view is strictly for operator situational awareness.

  1. Insert a Sensor () object using the Define Properties () method.
  2. When the Select Object window appears, select LEO_Sat in the list.
  3. Click OK .
  4. Select the Basic - Definition page.
  5. Set the following options:
    6. Option Value
    Sensor Type: Simple Conic
    Cone Half Angle: 2.8 deg
  6. Select the Basic - Pointing page.
  7. Set the following options:
    8. Option Value
    Pointing Type: Fixed
    Azimuth: 90 deg
    Elevation: 85 deg
  8. Click OK to accept changes and close the properties browser.

LEO satellite transmitter

Each LEO_Sat satellite has eighteen (18) user transmitter beams. In STK you have choices on how to simulate this configuration. In this tutorial, you’ll use the Multibeam Transmitter Model.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. When the Select Object window appears, select Sensor () in the list.
  3. Click OK .
  4. Rename the Transmitter object "LeoXmtr."

Define LeoXmtr's properties

  1. Open LeoXmtr's () properties ().
  2. Set the following properties:
    3. Option Value
    Type Multibeam Transmitter Model
    Beam Specs Frequency 14.51 GHz

Set the modulator options

  1. Select the Modulator tab.
  2. Select the Use Signal PSD checkbox.
  3. Set the Number of Spectrum Nulls to three (3).
  4. Click Apply .
  5. Select the Beams tab.
  6. Select the Antenna tab.
  7. Set the Design Frequency: to 14.51 GHz.
  8. Select the Orientation tab.
  9. Set the following changes:
    10. Option Value
    Azimuth: 0 deg
    Elevation: 89 deg
  10. Click Apply .

Define the beams

  1. In the Beams Selection Table at the top, click on Beam001 in the list.
  2. Click the Duplicate button seventeen (17) times so that you have a total of eighteen (18) Beams in the list.
  3. Select Beam001, hold down the Shift key, and then select Beam006.
  4. Click the Orient button.
  5. Set the following values in the Antenna Beam Orientation panel:
    6. Orientation Initial Value Increment Value
    Elevation: 89 deg 0 deg
    Azimuth: 0 deg 60 deg
  6. Click OK .
  7. Select Beam007, hold down the Shift key, and then select Beam018.
  8. Click the Orient button.
  9. Set the following values in the Antenna Beam Orientation panel:
    OrientationInitial ValueIncrement Value
    Elevation:88 deg0 deg
    Azimuth:0 deg30 deg
  10. Click  OK .
  11. Click OK to close LeoXmtr's () properties.

    12. You can generate an Antenna Properties report for the LEOXmtr to double-check the Beam values match the table below.

    Beam ID Azimuth Elevation
    Beam001 0 deg 89 deg
    Beam002 60 deg
    Beam003 120 deg
    Beam004 180 deg
    Beam005 240 deg
    Beam006 300 deg
    Beam007 0 deg 88 deg

    Beam008

    		 30 deg
    Beam009 60 deg
    Beam010 90 deg
    Beam011 120 deg
    Beam012 150 deg
    Beam013 180 deg
    Beam014 210 deg
    Beam015 240 deg
    Beam016 270 deg
    Beam017 300 deg
    Beam018 330 deg

Model the Walker constellation based on the template satellite

You want to model the LEOXmtr on each of the LEO_Sats. Do this by creating a Walker Constellation which includes the transmitters on each satellite.

  1. Right-click on LEO_Sat () in the Object Browser.
  2. Extend the Satellite menu.
  3. Select the Walker... option.
  4. Set the following values:
    OptionValue
    TypeDelta
    Number of Sats Per Plane10
    Number of Planes2
    Interplane Spacing1
    Color by PlaneOff
  5. Click the Create/Modify Walker button.
  6. Click Close once the satellites have all been created. This replicates the multibeam transmitter on each of the LEO_Sat satellites.
  7. Save the scenario.
  8. Delete LEO_sat () from the Object Browser.

LEO transmitter constellation

Group all of the LEO Transmitter objects into a Constellation object.

  1. Insert a Constellation () object using the Define Properties () method.
  2. In the Selection filter: enable Transmitter.
  3. Move () all Transmitter () objects to the Assigned Objects list.
  4. Remove GEO_Tx from the Assigned Objects list.
  5. Click OK to accept changes and close the properties browser.
  6. Rename the Constellation object “Interference_Sources."
  7. Save () the scenario ().

    8. 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.

View the LEO satellite constellation

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

LEO Satellite Constellation

Communication system and interference

Communications provides a CommSystem object that lets you identify interference sources and calculate the impact of interference on the communications links.

To set up a CommSystem object, you must first organize the relevant communication assets into three groups:

  • the transmitter(s) in the communications link of interest
  • the receiver(s) in the communications link of interest
  • the potentially interfering transmitters
  1. Insert two (2) Constellation () objects into the scenario using the Insert Default method.
  2. Rename the new Constellation objects: Transmitter and Receiver.

Model Receiver constellation

  1. Open Receiver’s () properties ().
  2. In the Basic - Definition page, move () the Receiver () object named Ship_Rx to the Assigned Objects list.
  3. Click OK .

Model Transmitter Constellation

  1. Open Transmitter’s () properties ().
  2. In the Basic - Definition page, move () the Transmitter () object named GEO_Tx to the Assigned Objects list.
  3. Click OK .

Build the Communications System

The CommSystem object models dynamically configured communications links between constellations of transmitters and receivers.

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

    2. If the Comm System object does not appear in the Insert Objects tool, click the Edit Preferences... button and add it.

  2. Rename the CommSystem object LEO_Interference.
  3. Open LEO_Interference’s () properties ().
  4. On the Basic - Transmit page, move () the Transmitter constellation to the Assigned Constellations column.
  5. Select the Basic - Receive page.
  6. Move () the Receiver constellation to the Assigned Constellations column.
  7. Select the Basic - Interference page.
  8. Move () the Interference_Sources constellation to the Assigned Constellations column.
  9. Click OK .
  10. Save () the scenario ().

Calculate Interference

You are now ready to calculate interference.

  1. In the Object Browser, right-click on LEO_Interference ().
  2. Open the CommSystem menu and click Compute Data.

    3. Depending on your computer, this could take a minute or two. You can view a progress bar in the lower right corner of STK.

  3. Open STK_SpectrumAnalyzer's () properties.
  4. Select the 2D Graphics - Global Attributes page.
  5. In the Vehicles section, clear the Show Ground Tracks / Routes and Show Orbits / Trajectories check boxes.

    6. This will declutter the 2D Graphics window.

  6. Click OK .
  7. Bring the 2D Graphics window to the front.

    8. You can see access lines between the ship's Receiver object, the GEO Satellite transmitter and LEO satellite Transmitter object(s).

  8. Click the Play () button in the Animation Toolbar to view these links dynamically.
  9. When you are finished, click the Reset () icon in the Animation Toolbar.

Potential Interference

LEO interference analysis

Use the Report & Graph Manager to determine if RF interference is affecting the ship's reception.

  1. In the Object Browser, right-click on LEO_Interference () and select Report & Graph Manager.
  2. Ensure the Object Type: field is set to CommSystem and LEO_Interference is selected in the Object List.
  3. In the Styles list, right-click on the My Styles folder
  4. Open the New menu, then select Graph ().
  5. Name the new graph "EbNo Interference" and then press the Enter key to open the graph's properties.
  6. In the Data Provider list, expand () Link Information.
  7. Select Eb/no and move () it to the Y Axis list.
  8. Return to the Data Provider list, select Eb/(No+Io) and move () it to the Y Axis list.
  9. Click OK .

Run the report

Now that you created the graph, let's generate it.

  1. Select EbNo Interference in the My Styles folder
  2. Click Generate... .
  3. Update the graph's Step size to one (1) sec.
  4. Refresh () the graph.

    5. Eb/No Interference

    You can see that there are two potential times that LEO satellite transmissions possibly interfere the ship's reception of the GEO satellite transmission.

Eb/No interference

  1. Using your mouse's left button, zoom in to the first spike in the graph.
  2. Right-click on the bottom of the spike and select Set Animation Time.
  3. If needed, go to the graph's toolbar and click the Toggle animation time line () icon in order to see the vertical time line in the graph.

    4. Eb/No with Time Line

    As you can see, the LEO satellite is decreasing the Eb/No.

Visualize the beams

You can view the beams in both the 2D and 3D Graphics windows.

  1. Open properties () of the LEO Transmitter () on LEO_Sat207 (LEOXmtr17) ().
  2. Select the 2D Graphics - Contours page.
  3. Select the Show Contour Graphics checkbox.
  4. In the Level Adding field, make the following changes:.
    5. Option Value
    Start: -3
    Stop: 0
    Step: 3
  5. Click Add Level .
  6. Change the Start Color to red and thicken the Line Width.
  7. Change the Stop Color to blue.
  8. Select the Set azimuth and elevation resolution together checkbox.
  9. Change the Azimuth Resolution to one (1) deg.
  10. Click Apply .

Enable contour graphics

  1. Select the 3D Graphics - Attributes page.
  2. In the Contour Graphics, select the Show Lines checkbox.
  3. Click OK to accept changes and close the properties browser.

View in 3D

  1. Bring the 3D Graphics window to the front.
  2. Zoom To LEO_Sat207 ().
  3. Use the left and right mouse buttons to move your view. You can see the antenna beams crosshairs inside the simple conic sensor’s field of view. LEO_Sat207 is interfering with communications between the ship and the GEO satellite.

3D View Multibeam Transmitter Pattern

  1. When you are finished, close the Report & Graph Manager.
  2. Leave the graph open.
  3. Save () the scenario.
     

Spectrum Analyzer

The Spectrum Analyzer is similar in nature to a real spectrum analyzer instrument, but with some additional features tailored toward STK. The Spectrum Analyzer enables you to view the spectrum utilization in different ways. It has various modes to help you understand the currently assigned emitter frequency allocations as well as when and how “hot” the spectrum band is currently being utilized. You can visualize the aggregate spectrum utilization and intensity from the perspective of what a specific receiver, at some geographical position, may encounter. It can show the emitters as itemized power spectrum densities at an instantaneous time or as an aggregate over a window of time.

  1. Click View on the Menu bar.
  2. Extend the Toolbars menu.
  3. Select Spectrum Analyzer.
  4. Click the Spectrum Analyzer () icon in the Toolbars section of the GUI.
  5. In the Spectrum Analyzer window's Transmitters field, select /Satellite/GEO_Sat/Transmitter/GEO_Tx and /Satellite/LEO_Sat207/Sensor/Sensor18/Transmitter/LEOXmtr17.
  6. Right-click on /Satellite/LEO_Sat207/Sensor/Sensor18/Transmitter/LEOXmtr17.
  7. Set the color to red and click OK .

Receiver view

  1. Select the Receiver View checkbox.
  2. Verify the Lock To Receiver check box is selected.
  3. Set the Vertical Scale to -160.

Data display

  1. Extend the Data Display menu on the Spectrum Analyzer Menu bar.
  2. Verify that the Peak and C/I options are selected.
  3. Extend the Edit menu on the Menu bar.
  4. Click Properties...
  5. Update the Sweep Line Width to three (3).
  6. Click OK .

Animate the scenario

  1. Decrease () the animation time step to 0.10 sec.
  2. Bring the EbNo Interference graph to the front.
  3. Zoom in further to the period that interference is taking place.
  4. Right click on the graph when the interference is just beginning and select Set Animation Time.

First Interference Period.

  1. Bring the Spectrum Analyzer back to the front.
  2. Start () the scenario and watch the interference dominate the desired signal for a short amount of time.

LeoXmtr17 Dominates GEO_Tx

  1. Bring the 3D Graphics window to the front.
  2. Zoom To Ship and view the non-nulled antenna pattern.

Non-nulled Phased Array Antenna Pattern

Null direction provider

The Phased Array Antenna Null Direction Provider tab enables you to select where the antenna points its nulls. This information is delivered to the beam former, which is responsible for forming and steering the beam toward the specified direction(s).

  1. Open Ship_Rx's () properties ().
  2. On the Basic - Definition page, select the Antenna tab
  3. Select the Null Direction Provider tab.

    4. This tab is within the Model Specs tab, which is itself within the Antenna tab

  4. In the Null Steering section, select the Enabled check box.
  5. Move () LEO_Sat207 from the left list to the right list. This is the satellite that is interfering with the ship's communications.
  6. Click OK .
  7. Bring the EbNo Interference graph to the front.
  8. Zoom out () on the graph until you can't zoom out any further.
  9. Refresh () the graph. Note that the first instance of interference has been reduced.
  10. Right click on the lowest spike during the first interference period and select Set Animation Time.

Nulling Effect Shown On Graph

  1. Return to the 3D Graphics window.

You can see how nulling the LEO transmitter has affected the view. The beam attempts to maintain access with the GEO transmitter while nulling the LEO Transmitter.

Nulled Antenna Pattern

On your own, you can determine which satellite is causing the second interference spike, use the Spectrum Analyzer to view the interference and then null the satellite causing the interference.

Save your work

  1. When you are finished, close all reports, the Report & Graph Manager and the Spectrum Analyzer.
  2. Save () your work.