Will My RF Receiver Experience Interference During a Range Test Flight?

STK Pro, STK Premium (Air), 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 STK Capabilities:

  • STK Pro
  • Communications
  • Radar

Problem statement

Engineers and operators need to quickly determine communication link budgets to:

  1. Analyze the telemetry downlink from a missile launch.
  2. Determine how various settings on a radar will affect its ability to track a missile.

In this lesson, a test will take place on board a stationary ship anchored off the Pacific Coast of the United States. A test missile will launch from a launch pad located on the Pacific Coast, and will download telemetry data to a communication systems on-board the ship. Telemetry data will transmit on a frequency which is close to a frequency being used by multiple XM satellites. Phase one of the test will determine if the XM satellite transmitters interfere with ship’s ability to receive the test missile telemetry data. Phase two of the test will determine if the a shipborne radar system can detect the missile during its flight. Custom radar cross section and radar antenna pattern files are required in the analysis.

Solution

Use STK's Communications capability to perform a preliminary analysis of both tests. Create the communication systems on the missile and the ship and determine if the XM satellite transmitters interfere with received telemetry data. If there is interference, use a spectrum filter to accurately model the power transfer from the interference source to the receiver. Build the ship's radar system that will track the missile. Use external radar cross section and antenna pattern files in the analysis to add realism to the scenario.

What you will learn

Upon completion of this tutorial, you will be able to:

  • Determine communication interference.
  • Use a Butterworth filter to mitigate communication interference.
  • Insert an external radar antenna pattern.
  • Apply an external radar cross section file for radar analysis.

Video guidance

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

Starter Scenario

To speed things up and allow you to focus on the portion of this exercise that teaches you how to determine communication interference and radar probability of detection, a partially created scenario has been provided for you.

  1. Ensure that the Welcome to STK dialog is visible in the STK Workspace.
  2. Click Open a Scenario .
  3. Browse to <STK Install Folder>\Data\Resources\stktraining\VDFs (e.g. C:\Program Files\AGI\STK 12\Data\Resources\stktraining\VDFs).

    4. If using an older version of STK, browse to <STK install folder>\Data\Resources\stktraining\samples and open MissileTest_XM_Interference.vdf.

  4. Select the file CommRadar_MissileTest_XM_Interference.vdf.
  5. Click Open.

Save the scenario

When you open the scenario, a directory with the same name as the scenario will be created in the default user directory (e.g. C:\Documents\STK 12. The scenario will not be saved automatically. When you save a scenario in STK, it will save in the format in which it originated. In other words, if you open a Visual Data (.vdf) file, the default save format will be a VDF. The same is true for a scenario file (*.sc). If you want to save a VDF as a SC file (or vice-versa), you must change the file format when you are performing the Save As procedure.

  1. Open the File menu and select Save As.
  2. Select STK User on the left side of the Save As window.
  3. Select CommRadar_Missile_Test_XM_Interference and click Open.
  4. Change Save as type: to Scenario Files (*.sc) and click Save.
  5. Click Yes to confirm.

Save often!

Insert the Test Missile

Create a missile that launches from the Pacific Coast and ditches in the ocean upon test completion.

  1. Using the Insert STK Objects Tool () insert a Missile () object using the Define Properties () method.
  2. Set the following options:
    3. Option Value
    Launch Latitude - Geodetic 34.7556 deg
    Launch Longitude -120.6223 deg
    Launch Altitude 8 ft
    Fixed Delta-V Use Default
    Impact Latitude - Geodetic 10 deg
    Impact Longitude 173 deg
    Impact Altitude 8 ft
  3. Click OK.
  4. Rename the Missile object () "Test_Missile".

View the Test Missile

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Test_Missile () in the Object Browser and select Zoom To.
  3. Mouse around in the 3D Graphics window to get a better view of Test_Missile ().

    4. Test Missile on Launch Pad

  4. In the Animation Toolbar, decrease () the Time Step to 1.00 sec (lower right hand corner of STK).
  5. Start () the animation and watch as Test_Missile () travels along its path.
  6. When you are finished, Reset () the scenario.

Altitude Versus Ground Range

You can determine the missile's flight time and other pertinent information using the Report & Graph Manager. There are a few reports that will provide the flight time but each report will provide different data concerning the missile itself (e.g. Altitude vs Ground Range, Beta Angle, Ephemeris-IFT-LLA, etc.). To keep it simple, generate an Altitude vs Ground Range report.

  1. In the Object Browser, right-click on Test_Missile () and select the Report & Graph Manager ().
  2. In the styles list, select and generate an Altitude vs Ground Range () report.
  3. Scroll through the report.
  4. Note the time that Test_Missile () impacts in the test range.
  5. When you are finished, close the report and the Report & Graph Manager ().

Test Missile's Transmitter

Test_Missile's () transmitter sends telemetry data to the ship.

  1. Using the Insert STK Objects Tool () insert a Transmitter () object using the Insert Default method.
  2. In the Select Object window, select Test_Missile () and click OK.
  3. Rename the Transmitter () object "Missile_Tx".

Transmitter Model Specs

Use a Medium Transmitter Model. The Medium Transmitter Model provides more flexibility by letting you specify gain and power separately instead of entering their product (EIRP) directly, as in the Simple model. It defaults to an omnidirectional antenna with constant gain. An omnidirectional antenna radiates uniformly in all directions. A gain of zero (0) dB is representative of a theoretical perfect transmitter system.

  1. Open Missile_Tx's () Properties ().
  2. Select the Basic - Definition page.
  3. Set the following options:
    4. Option Value
    Type: Medium Transmitter Model
    Frequency: 2.41 GHz
    Power: 80 W (Watts)
    Gain: -0.57 dB
    Data Rate: 2.048 Mb/Sec
  4. Click Apply.

Transmitter Modulator

The transmitter will use Bi-phase shift keying (BPSK). You will use the Power Spectral Density (PSD). PSD is used to determine the Bandwidth Overlap Factor. By using signal PSD, you combine the entire signal including losses in your analysis. The nulls are where the main lobe and side lobes drop to zero. If this option is not selected, the PSD will be modeled as a flat spectrum with unity magnitude across the transmitter’s bandwidth.

  1. Select the Modulator tab.
  2. Set the Modulator type to BPSK.
  3. Enable the Use Signal PSD option.
  4. Click OK.

Steerable Antenna

In STK, a Sensor () object can be used as a motor to steer an Antenna () object. In this instance, it will act as the ship receiver's steering motor. The receiver will accept Missile_Tx's () telemetry transmissions.

  1. Using the Insert STK Objects Tool () insert a Sensor () object using the Insert Default method.
  2. In the Select Object window, select Ship () and click OK.
  3. Rename the Sensor () object "Antenna_Motor".

Define the Sensor's Cone Half Angle

The Sensor () object's field of view is not being used for anything other than situational awareness. In order to see it, but keep it from obstructing other views in the 3D Graphics window, minimize its cone half angle.

  1. Open Antenna_Motor’s () properties ().
  2. Select the Basic - Definition page.
  3. Set the Cone Half Angle to five (5) degrees.
  4. Click Apply.

Antenna Location

Add realism to the analysis by placing the antenna motor at its actual location on the ship.

  1. Select the Basic - Location page.
  2. Set the following options:
    3. Option Value
    Location Type: Fixed
    X: 75 ft
    Z: 75 ft
  3. Click Apply.

Target the Test Missile

Next, target the test missile.

  1. Select the Basic - Pointing page.
  2. Set the Pointing Type: to Targeted.
  3. In the Available Targets list, move () Test_Missile () to the Assigned Targets list.
  4. Click OK.
  5. Bring the 3D Graphics Window to the front.
  6. In the Object Browser, right-click on Ship () and select Zoom To.
  7. Decrease () the Time Step: to 1.00 sec.
  8. Start () the animation. When Antenna_Motor () accesses Test_Missile (), it will be visible. Note its location on the ship.

    9. Sensor Targeting Test Missile

  9. When you are finished, Reset () the scenario.

Test Ship's Receiver

Use a Receiver () object to receive telemetry transmissions from the missile. Use a complex receiver model employing the Auto Track option.

  1. Using the Insert STK Objects Tool () insert a Receiver () object using the Insert Default method.
  2. In the Select Object window, select Antenna_Motor () and click OK.
  3. Rename the Receiver () object "Ship_Rx".

Receiver Model Specs

Ship_Rx () is going to accept the telemetry data from Missile_Tx (). The Complex Receiver model allows you to select among a variety of analytical and realistic antenna models, and to define the characteristics of the selected antenna type

  1. Open Ship_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Set the following options:
    4. Option Value
    Type: Complex Receiver Model
    Auto Track On (default)
  4. Click Apply.

Receiver Antenna

The receiver uses a Helix Antenna Pattern.

  1. Select the Antenna tab.
  2. Set the following options:
    3. Option Value
    Type: Helix
    Design Frequency: 2.5 GHz
    Diameter: 0.9 m
    Turn Spacing: 1 mm
    Number of Turns: 3
  3. Click Apply.

Visualize the Antenna Pattern

You can visualize antenna patterns in STK.

  1. Select the 3D Graphics - Attributes page.
  2. Set the following options:
Option Value
Volume Graphics - Show Volume On
Volume Graphics - Gain Scale (per dB) 0.5 km
Pattern - Set Azimuth and elevation resolution together On
Azimuth - Resolution 1 deg

Gain Coloring

There are two methods for specifying how colors will be added to show antenna gain. Use the Explicit Levels Method to define individual antenna gain levels.

  1. In the Gain Coloring field, set the Method to Explicit Levels.
  2. Set the following Level Adding options:
    3. Option Value
    Relative to Maximum On
    Start -70 (dB)
    Stop 0 (dB)
    Step 10 (dB)
  3. Click Add Levels.
  4. Click Apply.
  5. Bring the 3D Graphics Window to the front.
  6. In the Object Browser, right-click on Ship () and select Zoom To. Your antenna pattern colors might not look the same as the colors in the illustration.
  7. Start () the animation. When Antenna_Motor () accesses Test_Missile (), the antenna pattern will be visible. You may want to zoom out a bit.

    8. Helix Antenna Pattern

  8. When you are finished, Reset () the scenario.
  9. Return to Ship_Rx's () properties ().
  10. Clear the Show Volume option.
  11. Click OK.

Analyze the Telemetry Downlink

The missile will transmit telemetry data to the ship during its flight. Determine if there is a connection between the ship’s receiver and the missile’s transmitter. The link budget report gives you the signal strength and quality of the link received at the ship from the missile.

  1. Select Ship_Rx () in the Object Browser.
  2. Click Access tool () on the STK Tools toolbar.
  3. In the Associated Objects List expand () the Object Tree under Test_Missile.
  4. Select Missile_Tx ().
  5. Click Link Budget .
  6. Scroll to the right until you find the column BER (Bit Error Rate).
  7. Scroll down through the column.

For the purposes of this analysis, a Bit Error Rate of 1.000000e-09 or lower is acceptable. For the most part, you have good reception from the missile to the ship. As the missile gets further from the ship, the Bit Error Rates increase. However, the link budget report doesn't take potential XM satellite radio frequency interference into account. For that, you need the CommSystem () Object.

When finished, close the report and the Access () tool.

Determine Potential Interference

Communications provides a CommSystem () object that allows you to model dynamically configured communications links between constellations of transmitters and receivers. The CommSystem () object lets you identify interference sources and calculate the impact of interference on the communications link.

To set up a CommSystem () object, you must first organize the relevant communications 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 transmitter(s)

This grouping is accomplished with the help of the Constellation () object.

Transmitter Constellation

Place the missile transmitter into a single constellation.

  1. Using the Insert STK Objects Tool () insert a Constellation () object using the Define Properties method.
  2. Move () Missile_Tx () from the Available Objects list to the Assigned Objects list.
  3. Click OK.
  4. Rename the Constellation () object "Transmitter".

Receiver Constellation

Place the ship’s receiver into a single constellation.

  1. Using the Insert STK Objects Tool () insert a Constellation () object using the Define Properties method.
  2. Move () Ship_Rx () from the Available Objects list to the Assigned Objects list.
  3. Click OK.
  4. Rename the Constellation () object "Receiver".

Interference Constellation

The interference constellation will have the transmitters that are potentially interfering with the telemetry data.

  1. Using the Insert STK Objects Tool () insert a Constellation () object using the Define Properties method.
  2. Move () XM3_Tx (), XM4_Tx () and XM5_Tx () from the Available Objects list to the Assigned Objects list.
  3. Click OK.
  4. Rename the Constellation () object "Interference".

Configure the Comm System Object

Using the constellations you just created, you can now build the CommSystem () object. Once you have the CommSystem () object configured, you can determine if the XM transmitters are interfering with the telemetry data being transmitted from the test missile to the ship.

If the CommSystem () object is in the Insert STK Objects () Tool, move to step five (5). If you don't have a CommSystem () object in the Insert STK Objects () tool, you can add it by performing steps one (1) through four (4).

  1. In the Insert STK Objects tool (), click Edit Preferences.
  2. When the Preferences window opens, find the Define Default Creation Methods field.
  3. In the (Check the "Show" item to display the object in the "New Object" tool) field, locate and enable Comm System.
  4. Click OK.
  5. Use the Insert STK Objects Tool () to insert a Comm System () object using the Define Properties method.
  6. On the Basic - Transmit page, move () the Transmitter () constellation from the Available Constellation list to the Selected Constellation list.
  7. Browse to the Basic - Receive page.
  8. Move () the Receiver () constellation from the Available Constellation list to the Selected Constellation list.
  9. Browse to the Basic - Interference page.
  10. Move () the Interference () constellation from the Available Constellation list to the Selected Constellation list.
  11. Click OK.

Check for Interference

Compute the CommSystem () object to determine if the XM satellites will interfere with the telemetry data.

  1. Save () your scenario.
  2. Select CommSystem1 () in the Object Browser.
  3. Open the CommSystem menu item in the STK menu area and select Compute Data.

    4. A progress bar will appear in the lower right corner of STK. When the progress bar reaches 100%, it will disappear. Your calculation is complete.

  4. Return to the Object Browser, right-click on CommSystem1 () and select Report & Graph Manager ().
  5. In the Styles list, ensure Show Reports is enabled.
  6. Select the Link Information Detailed report () and click Generate.
  7. At the top of the report, click Show Step Value .
  8. Change Step: to 1 sec.
  9. Locate the BER and BER+I columns.
  10. BER+I is Bit Error Rate plus Interference.
  11. Scroll down through the report and compare both columns.

    12. In this analysis, you require a BER of 1.0000e-09 or lower. You can see that the XM transmitters will interfere with the telemetry data being transmitted from the test missile to the ship. Note at what time interference raises the BER above 1.0000e-09 (e.g. 8 Jan 2018 16:00:25.000).

  12. Leave the report open.
  13. Close the Report & Graph Manager ().

Spectrum Filter

Having determined that the XM satellites will interfere with the ship's receiver, you can apply a spectrum filter.

Applying a spectrum filter reduces the effect of the interference on the communication link. Suppressing the XM satellite's signal at the receiver, the telemetry link should perform better in the presence of the interference.

A spectrum filter can be used to accurately model the power transfer from a transmitter to a receiver or an interference source to a receiver. This can be handy when trying to model adjacent band interference or for evaluating link performance for a given specific power spectrum mask.

Adding a filter to a receiver will shape the received PSD by multiplying it by the selected receiver filter’s frequency response.

Butterworth Filter

Use a Butterworth Filter. The Butterworth Filter has a flat passband and has a moderately steep roll off. It will suppress anything that falls outside of the passband. Ideally, you would like to filter out any satellite interference under five (5) MHz. However, this could be adjusted if required.

  1. Open Ship_Rx’s () properties ().
  2. Select the Basic - Definition page.
  3. Select the Filter tab.
  4. Enable the Use option in the Filter Model section.
  5. Ensure Butterworth is selected.
  6. Set the Cut-off Frequency: to a value of 5 MHz.
  7. Click OK.

Recompute the CommSystem Object Link Budget

Check the effect of filtering on the signal quality.

  1. Bring the Link Information Detailed report to the front.
  2. Refresh () the Report Data window.
    • At what time does the interference take affect?
    • By how much does the interference affect the signal?

    Notice that BER with interference (using filtering) shows improvement in link performance over BER with interference (without filtering).

    You will see approximately a 50 db of improvement in the Eb/(No + Io) with the Butterworth filter. With the Butterworth filter, the ship can receive the missile’s transmissions a few minutes longer. You could further tweak the values but this would be based on acceptable changes to your bandwidth.

  3. When finished, close the report.
  4. In the Object Browser, uncheck Antenna_Motor () and CommSystem1 ().
  5. Expand the Analysis menu and select Remove All Accesses.
  6. Save the scenario.

The Radar

The second phase of the test determines if the ship's radar can track the test missile.

  1. Using the Insert STK Objects Tool () insert a Radar () object using the Insert Default method.
  2. In the Select Object window, select Ship () and click OK.
  3. Rename the Radar () object "Ship_Radar".

Radar Mode

Track the missile by sending pulses to determine probability of detection. The radar continues to send pulses until it meets an assigned signal to noise ratio goal. At the end of sending the pulses, if none of them hit the missile, then the radar did not detect the missile.

  1. Open Ship_Radar's () properties.
  2. On the Basic - Definition page, ensure the Mode tab is selected and the Type: is set to Search Track.
  3. In the Waveform tab, select the Pulse Definition tab.
  4. Set Pulse width to 880 nsec (nanoseconds).
  5. Select the Pulse Integration tab.
  6. Set SNR: to 20 dB.
  7. Note the Maximum Pulses: value of 512.
  8. Click Apply.

Radar Antenna

The ship's tracking radar is similar to an airfield surveillance radar which spins, covering a 360 degree field-of-view. Use an external antenna pattern file that models the field of view of this type of radar.

  1. Select the Antenna tab.
  2. In the Model Specs tab, set the Type: to External Antenna Pattern.
  3. Set the Design Frequency: to 2.8 GHz.
  4. Click the External Filename: ellipsis ().
  5. Browse to <STK Install Folder>\Data\Resources\stktraining\samples.
  6. Select the ASR9Low.pattern file.
  7. Click Open.
  8. Click Apply.

Radar Antenna Location

The radar is located at the top of the ship's mast.

  1. Select the Orientation tab.
  2. Set the following Position Offset values:
    3. Option Value
    X: 37 ft
    Z: 120 ft
  3. Click Apply.

Radar Transmitter

  1. Select the Transmitter tab.
  2. Set the following options:
    3. Option Value
    Frequency on / 2.8 GHz
    Power: 11 GW
  3. Click Apply.

Radar Receiver

Add low noise amplifier gain to the receiver.

  1. Select the Receiver tab.
  2. Change LNA Gain: to 25 dB.
  3. Click OK.

Missile Radar Cross Section

Define the missile's radar cross section (RCS) using an external RCS file.

  1. Open Test_Missile's () properties ().
  2. Select the RF - Radar Cross Section page..
  3. Disable Inherit
  4. Change Compute Type: to External File.
  5. Click the Filename: ellipses () .
  6. Browse to <STK Install Folder>\Data\Resources\stktraining\samples.
  7. Select the Basic_Missile_mono.rcs file.
  8. Click Open.
  9. Click OK to accept the changes and close Test_Missile's () properties ().

Create an Access

Determine if the ship's radar can track the test missile.

  1. In the Object Browser, right-click on Ship_Radar () and select Access.
  2. Select Test_Missile () as the Associated Object.
  3. Click Compute.
  4. Click Report & Graph Manager .

Custom Report

Create a custom report that shows azimuth-elevation-range (AER) and Radar Search/Track data.

  1. Select the MyStyles directory.
  2. Click Create new report style () .
  3. Rename the report AER and Search Track Data.
  4. Click Enter on your keyboard.

Data Providers

The AER Data data provider provides azimuth, elevation, and range related information for the relative position vector between the base object and the target object. The information is available in a variety of coordinate axes.

  1. In the Data Providers section, expand () AER Data.
  2. Expand () BodyFixed.
  3. Move () the following to the Report Contents section in the order shown:
    • Time
    • Azimuth
    • Elevation
    • Range

Search/Track Properties report all the settings in the Radar Basic->Search/Track property page.

  1. Expand () Radar SearchTrack.
  2. Move () the following to the Report Contents section in the order shown:
  • S/T Integrated SNR: Signal quality of return from the radar.
  • S/T Integrated PDet: Is the missile detected.
  • S/T Pulses Integrated: Number of pulses needed to detect the missile.

Radar RCS reports on radar cross section settings.

  1. Expand () Radar RCS.
  2. Move () RCS to the Report Contents section.
  3. Click OK.

Set the time period

Now that the data providers have been defined, you can set the time period.

  1. Enable the Specify Time Properties option.
  2. Set the following options:
    3. Option Value
    Start: 8 Jan 2018 16:00:00.000 UTCG
    Stop: 8 Jan 2018 16:00:20.000 UTCG
    Use step size / time bound on
    Step size: .1 sec
  3. Click Generate.

Notice how long you can track the test missile basing it on a S/T Integrated PDet of 0.8 or higher (~ 16 seconds). Also note the change in azimuth, elevation, and range as the missile travels.

Save Your Work

  1. When finished, Reset () the scenario and close any reports or tools that are still open.
  2. Save () your work.

Summary

A You determined that a portion of test missile's telemetry data was interfered with by the XM satellite transmissions. By using a Butterworth filter, you were able to somewhat mitigate the interference. Using an external antenna pattern (ideally designed for a particular radar), you created an on-board ship radar that functioned similar to an air surveillance radar. You applied an external radar cross section file to the test missile (ideally designed for a particular missile type). Creating a custom report, you determined that the ship's radar was able to track the test missile for approximately sixteen seconds of flight.

On Your Own

Change radar settings such as transmitter frequency and power, or receiver pre-received gains or losses to determine their effects on your probability of detection. Experiment with the Butterworth filter to determine if you can mitigate further the interference in the link budget. Keep the current settings but change the test missiles flight path (e.g. impact point, apogee altitude, etc.).