Fundamentals of STK Communications

This tutorial introduces some of the functionality of the STK Communications module.

STK Professional and Communications.

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.

Create a Scenario

Start by creating a scenario.

  1. Create a scenario and name it Communications.
  2. Change the Start: to 1 Jul 2016 18:00:00.000 UTCG.
  3. Change the Stop: to 2 Jul 2016 18:00:00.000 UTCG

Save Often!

Turn Off Terrain

  1. Open Communication’s properties.
  2. Browse to the Basic – Terrain page.
  3. Turn off Use terrain server for analysis.
  4. Click OK.

Communication Ground Site

Begin populating the scenario with objects required to analyze communications. A ground site is required.

  1. Use the Insert STK Objects tool () to insert a Facility () object using the Insert Default method.
  2. Name the Facility object CommFac.
  3. Open CommFac's () properties () to the Basic - Position page and make the following changes:
    4. Option Value
    Latitude 41.1089 deg
    Longitude -95.911 deg
  4. Click OK.

Communication Satellite

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

  1. Use the Insert STK Objects tool () to insert a Satellite object () using the Orbit Wizard method.
  2. Make the following changes:
    3. Option Value
    Type: Geosynchronous
    Satellite SatComm
    Subsatellite Point: -100 deg
    Inclination: 10 deg
  3. Click OK.

Transmitter

To keep things at the basic level, begin with a simple transmitter.

  1. Use the Insert STK Objects tool () to insert a Transmitter () object using the Insert Default method.
  2. When the Select Object window opens, select SatComm () and click OK.
  3. Rename the Transmitter object Downlink.
  4. Open Downlink's () properties ().
  5. On the Basic - Definition page, make the following changes in the Model Specs tab:
Option Value
Frequency: 5 GHz
EIRP: 5 kW
Data Rate: 1 Mb/sec
  1. Select the Modulator tab and change Name: to QPSK.
  2. Click OK.

Receiver

Stay at the basic level by using a simple receiver.

  1. Use the Insert STK Objects tool () to insert a Receiver () object using the Insert Default method.
  2. When the Select Object window opens, select CommFac () and click OK.
  3. Rename the Receiver object DLRcvr.
  4. Open DLRcvr's () properties ().
  5. On the Basic - Definition page, in the Model Specs tab, change G/T to 6 dB/K.
  6. Click OK.

Determine Link Performance

Use a simple link budget to focus on Bit Error Rates.

  1. In the Object Browser, right click on DLRcvr and select Access... to open the Access Tool ().
  2. In the Associated Objects list, expand SatComm and select Downlink.
  3. In the Reports field, click Link Budget...
  4. Scroll to the right and locate the BER column.
  5. Scroll down and notice how the BER values fluctuate.
  6. Close the report.

Custom Graph

The fluctuations in the bit error rates are likely caused by the satellite's inclination change which increases the range. Create a custom graph to compare range to bit error rates.

  1. Return to the Access Tool ().
  2. Click the Report & Graph Manager... button.
  3. In the Styles list, right click on the My Styles folder, select New and click Graph.
  4. Rename the graph Range and BER.
  5. Click the Enter key to open Range and BER's properties.
  6. In the Data Providers list, expand AER Data and then Default.
  7. Move () Range to the Y Axis field.
  8. Return to the Data Providers list and expand Link Information.
  9. Move () BER to the Y2 Axis field.
  10. Click OK.
  11. In the Styles list, select Range and BER and click Generate.
  12. Close the graph, the Report & Graph Manager and the Access Tool.
  13. Save () your scenario.

Looking at the custom graph, you can see that there is a direct correlation between the range of the satellite to increases in the bit error rate.

Antenna Object

There are two ways to use antennas in STK: Embed or Link. The embedded antennas are defined within the properties of a parent receiver or transmitter. These antennas are specific to that parent object, which means that they cannot be used by multiple transmitters/receivers.

The linked antennas are defined independently of any single receiver or transmitter, which enables the sharing of the antenna by several transmitters and receivers. If you have multiple transponders attached to a communication satellite, aircraft, ship, etc., you can create a single antenna object, and have the transmitters and receivers link to the one antenna. This is convenient for two reasons:

  • The parameters of the antenna object only have to be defined once on the Antenna object, rather than reentered for each receiver and transmitter.
  • When changing the properties of the Antenna object, this can be done once on the linked Antenna object, rather than reentered for each receiver and transmitter.

Continuing with the current scenario, you'll create an uplink transmitter at the CommFac and an uplink receiver on the SatComm. Instead of using the embedded antennas for all your transmitters and receivers, you will share one antenna on the ground site and one antenna on the satellite using the Antenna object.

Satellite Antenna

You have a downlink transmitter attached to CommSat. The Transmitter object is using its embedded antenna. Using the Antenna object, you will create one antenna which is being shared by the Transmitter object and a Receiver object.

  1. Use the Insert STK Objects tool () to insert an Antenna () object using the Insert Default method.
  2. When the Select Object window opens, select SatComm () and click OK.
  3. Rename the Antenna object SatAnt.
  4. Open SatAnt's () properties ().
  5. On the Basic - Definition page, make the following changes:
    6. Option Value
    Design Frequency 2.5 GHz
    Diameter 2 m
  6. Browse to the Basic - Orientation page. The satellite's antenna is bore sighted.
  7. On the Basic - Orientation page, make the following changes:
    8. Option Value
    Azimuth: 275 deg
    Elevation: 84 deg
  8. Browse to the 2D Graphics - Boresight page.
  9. Enable Show Boresight Graphics. This enables you to see the marker on the 2D Graphics window.
  10. Click OK.

View Communications in the Graphics Windows

  1. Bring the 2D Graphics window to the front and open its properties.
  2. Browse to the Details page.
  3. In the Map Details field, enable RWDB2_International_Borders and RWDB2_Provincial_Borders.
  4. Click OK.
  5. Click the Reset button () in the Animation toolbar. You should see an X in the Southeast corner of Colorado. That's the antenna boresight location.
  6. Press Start () in the Animation toolbar and watch the antenna boresight. The antenna boresight moves due to the inclination of the parent satellite.
  7. Click the Reset () button in the Animation toolbar when finished.

Satellite Receiver and Transmitter

You need a receiver that receives up-linked data from the ground site.

  1. Use the Insert STK Objects tool () to insert a Receiver () object using the Insert Default method.
  2. When the Select Object window opens, select SatComm () and click OK.
  3. Rename the Receiver object ULRcvr.

Link the Antenna Object

  1. Open ULRcvr's () properties ().
  2. On the Basic - Definition page, change Type: to Complex Receiver Model.
  3. Select the Antenna tab.
  4. Change Reference Type: to Link.
  5. Click OK.

You can see that Reference Type: defaults to Embed. If you kept the default, you would be required to build an antenna. However, you can use the Antenna object which you built earlier in the scenario.

You can see the Antenna object properties have imported into the Receiver objects properties.

Transmitter

Now you will link the Transmitter object to the Antenna object.

  1. Open Downlink's () properties ().
  2. On the Basic - Definition page, change Type: to Complex Transmitter Model.
  3. In the Model Specs tab, make the following changes:
    4. Option Value
    Frequency: 5 GHz
    Power: 10 dBW
  4. Select the Antenna tab.
  5. Change Reference Type: to Link.
  6. Click OK.

Ground Site Antenna

You have a downlink receiver attached to CommFac. The Receiver object is using its embedded antenna. Using the Antenna object, you will create one antenna which is being shared by the Receiver object and a Transmitter object.

Unlike the satellite antenna which is boresighted, the ground site antenna can track its target. To do this in STK, you will use a Sensor object as a servomotor.

  1. Bring the 3D Graphics window to the front.
  2. In the Object Browser, right click on CommFac () and select Zoom To.
  3. Use the Insert STK Objects tool () to insert a Sensor () object using the Insert Default method.
  4. When the Select Object window opens, select CommFac () and click OK.
  5. Rename the Sensor object Servomotor.
  6. Open Servomotor's () properties ().
  7. On the Basic - Definition page, change the Cone Half Angle to 2 deg.
  8. Browse to the Basic - Pointing page.
  9. Change the Pointing Type: to Targeted.
  10. Move SatComm () from the Available Targets list to the Assigned Targets list using the right arrow.
  11. Click OK.
  12. Return to the 3D Graphics window to view Servomotor pointing at SatComm.

Create the Antenna

You can see that the sensor is pointing at the satellite. Now you can create the antenna.

  1. Use the Insert STK Objects tool () to insert an Antenna () object using the Insert Default method.
  2. When the Select Object window opens, select Servomotor () and click OK.
  3. Rename the Antenna object FacAnt.
  4. Open FacAnt's () properties ().
  5. On the Basic - Definition page, make the following changes:
    6. Option Value
    Design Frequency: 2.5 GHz
    Diameter: 4 m
  6. Click OK.

Ground Site Receiver and Transmitter

You need a transmitter that uplinks data to the satellite.

  1. Use the Insert STK Objects tool () to insert a Transmitter () object using the Insert Default method.
  2. When the Select Object window opens, select CommFac () and click OK.
  3. Rename the Transmitter object Uplink.
  4. Open Uplink's () properties ().
  5. On the Basic - Definition page, change Type: to Complex Transmitter Model.
  6. In the Model Specs tab, make the following changes:
    7. Option Value
    Frequency: 4 GHz
    Power: 10 dBW
  7. Select the Antenna tab.
  8. Change Reference Type: to Link.
  9. Click OK.

Receiver

Now you will link the Receiver object to the Antenna object.

  1. Open DLRcvr's () properties ().
  2. On the Basic - Definition page, change Type: to Complex Receiver Model.
  3. Select the Antenna tab.
  4. Change Reference Type: to Link.
  5. Click OK.

Link Budget

You will be concentrating on an examination of the antenna Eb/No and the Bit Error Rate (BER). To check these values, create a Link Budget Report.

  1. In the Object Browser, right click on DLRcvr () and select Access... to open the Access Tool.
  2. In the Associated Objects list, expand SatComm () and select Downlink ().
  3. In the Reports field, click Link Budget...
  4. Scroll to the right and locate the Eb/No (dB) and BER columns.

As you scroll through the values you will see that the link budget is much improved. This is due to using a targeted antenna.

Save Your Work!

  1. Close the link budget report and the Access Tool.
  2. If desired, follow the above steps to create a link budget between Uplink and ULRcvr.
  3. When finished, close the link budget report and the Access Tool ().
  4. Save () your scenario.

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