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.

This lesson requires an internet connection to complete in its entirety.

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
  • Communications
  • Radar

Problem statement

Engineers and operators need to quickly model and analyze a telemetry link from a missile launch and to determine how various settings on a radar will affect its ability to track a missile. You are launching a test missile from a launch pad located on the Pacific Coast of the United States. The missile will transmit telemetry data to a communications system on board a ship anchored off the coast. The missile's telemetry data will be transmitted on an S-band frequency, which is close to a frequency used by multiple high-power satellite digital audio radio service (SDARS) satellites. Phase one of your test will determine if the satellites, which provide XM radio service, will interfere with ship's ability to receive the test missile telemetry data. Phase two of your test will determine for how long a shipborne radar system can detect and track the missile during its flight. A custom radar cross section and a radar antenna pattern file are required for your analysis.

Solution

Use the STK software's Communications capability to perform a preliminary analysis of both tests. Model the communication systems on the missile and the ship, compute a link budget, and determine if the SDARS 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. Using the Radar capability, model 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 your model.

What you will learn

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

  • Model and analyze communications interference in a radio frequency (RF) receiver
  • Use a Butterworth filter to mitigate communications interference
  • Insert an external radar antenna pattern
  • Use an external radar cross section file for radar analysis

Creating a new scenario

First, you must create a new scenario, then build from there.

  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 CommRadar_MissileTest_Interference
    Location Default
    Start Use the default date / set the time to 16:00.00.000 UTCG
    Stop + 35 min
  4. Click OK when you finish.
  5. Click Save () when the scenario loads.

    6. A folder with the same name as your scenario is created for you.

  6. Verify the scenario name and location when the Save As dialog box opens.
  7. Click Save.

Save () often during this lesson!

Disabling streaming terrain

By default, the STK application connects to the Ansys Geospatial Data Cloud to distribute Earth terrain data for analysis and visualization. Turn off streaming terrain, as it is not required for your analysis.

  1. Right-click on CommRadar_MissileTest_Interference () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Terrain page when the Properties Browser opens.
  4. Clear the Use terrain server for analysis check box in the Terrain Server panel.
  5. Click OK to confirm your change and to close the Properties Browser.

Modeling the test missile

Your missile will launch from Vandenberg Space Force Base in California and will ditch in the ocean in the Western Range upon completion of the test.

Inserting a new Missile object

Insert a new Missile object into your scenario. A Missile object models the properties and behavior of a vehicle following an elliptical path that begins and ends at the surface of a central body.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Missile () in the Select An Object To Be Inserted list.
  3. Select Define Properties () in the Select A Method list.
  4. Click Insert....

Designing the Missile object's trajectory

The Ballistic Propagator defines an elliptical path that begins and ends at the Earth's surface. Specifying a fixed flight time, initial velocity or altitude can further refine the shape of the trajectory.

  1. Select the Basic - Trajectory page when the Properties Browser opens.
  2. Notice that the default Propagator is Ballistic.
  3. Set the following options:
    4. Option Value
    Launch Latitude - Geodetic 34.7556 deg
    Launch Longitude -120.6223 deg
    Launch Altitude 8 ft
    Fixed Delta-V Default (6.90194 km/sec)
    Impact Latitude - Geodetic 10 deg
    Impact Longitude 173 deg
    Impact Altitude 8 ft
  4. Click OK to confirm your changes and to close the Properties Browser.
  5. Right-click on Missile1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename Missile1 () Test_Missile.

Viewing the test missile

View the test missile in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Test_Missile () in the Object Browser.
  3. Select Zoom To in the shortcut menu.
  4. Move around in the 3D Graphics window to get a better view of Test_Missile ().
  5. Click Decrease Time Step () in the Animation toolbar, and set the Time Step to 1.00 sec.
  6. Click Start () to animate the scenario.
  7. Watch as Test_Missile () travels along its path.

    8. Test Missile in Flight

  8. Click Reset () when finished.

Generating an Altitude vs Ground Range report

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. To keep it simple, generate an Altitude vs Ground Range report.

  1. Right-click on Test_Missile () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Altitude vs Ground Range () report style, located in the Installed Styles () folder in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate....
  5. Scroll through the report.
  6. Note that Test_Missile () will impact the ocean at the end of its arc, approximately 32 minutes after launch.
  7. When you are finished, close the Altitude vs Ground Range report.
  8. Click Close to close the Report & Graph Manager.

Modeling the test missile's transmitter

A transmitter on Test_Missile will send telemetry data to the ship.

Inserting a Transmitter object

Attach a Transmitter object to Test_Missile. A Transmitter object models the characteristics of the transmitter, the antenna it uses, and the environment in which it operates.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Transmitter () object using the Insert Default () method.
  3. Select Test_Missile () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Transmitter1 () Missile_Tx.

Using a Medium Transmitter model

A Medium Transmitter model provides you flexibility by letting you specify gain and power separately, instead of entering their product (the effective isotropic radiated power, or EIRP) directly, as in a Simple Transmitter model. The Medium Transmitter model uses an isotropic, omnidirectional antenna, which is an ideal spherical pattern antenna with constant gain. 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 when the Properties Browser opens.
  3. Click the Transmitter Model Component Selector ().
  4. Select Medium Transmitter Model () in the Transmitter Models list when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Select the Model Specs tab.
  7. Set the following transmitter specifications:
    8. Option Value
    Frequency 2.31 GHz
    Power 80 W
    Gain -0.57 dB
    Data Rate 2.048 Mb/Sec
  8. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the transmitter modulation options

The STK application features a number built-in common analytical modulators and can compute their power spectral density (PSD) characteristics analytically. The missile's transmitter uses bi-phase shift keying (BPSK).

  1. Select the Modulator tab.
  2. Leave the Modulator type set to BPSK.
  3. Select the Use Signal PSD check box.

    4. The 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.

  4. Click OK to confirm your selection and to close the Properties Browser.

Modeling the ship

The ship is anchored off the coast of California. It will function as the test location for your communications and radar equipment.

Inserting a new Ship object

Insert a Ship object into your scenario.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Ship object () using the Insert Default () method.
  3. Rename Ship1 () Ship.

Defining the ship's route options

Manually define the ship's route by providing the waypoints, the altitude reference, and all other values that define the route.

  1. Open Ship's () Properties ().
  2. Select the Basic - Route page when the Properties Browser opens.
  3. Use the default GreatArc propagator.
  4. Open the Route Calculation Method drop-down list.
  5. Select Specify Time.

    6. The ship will remain stationary for the duration of your scenario. Specify Time uses the Time properties of each waypoint.

  6. Open the Reference drop-down list in the Altitude Reference panel.
  7. Select WGS84.

    8. Since you've disabled analytical terrain, you want the ship to sit on the surface of the WGS84 ellipsoid.

Defining the ship's waypoints

Now, add the waypoints for the ship's route. The ship will remain stationary, so you can define a route using two waypoints set at the same location over the course of your analysis period.

  1. Click Insert Point.
  2. Set the following options for the first waypoint:
    3. Option Value
    Latitude 34.196 deg
    Longitude -120 deg
  3. Click Insert Point again.
  4. Set the second waypoint's time to be 35 minutes from the first point's time (for example, [Date] 16:35:00.000 UTCG).

    5. You want to be sure the ship remains stationary for the duration of your analysis period.

  5. Click OK to confirm your changes and to close the Properties Browser.

Inserting a Sensor object

A Sensor object can be used to model a servo motor to steer an antenna, be it an Antenna object or an analytical antenna embedded in another communications object. In this instance, it will act as the ship's RF receiver antenna's steering motor. The receiver will accept Missile_Tx's incoming telemetry transmissions.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Sensor () object using the Insert Default () method.
  3. Select Ship () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Sensor1 () Antenna_Motor.

Defining the sensor's cone half angle

Antenna_Motor's field of view is not being used for anything other than situational awareness. In order to see it, but to keep it from obstructing other views in the 3D Graphics window, minimize its cone half-angle by updating the sensor's Definition properties.

  1. Open Antenna_Motor's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Enter 5 deg in the Cone Half Angle field in the Simple Conic panel.
  4. Click Apply to confirm your change and to keep the Properties Browser open.

Setting the antenna motor's location

Update the sensor's Location properties to position the antenna motor near its actual location on the ship.

  1. Select the Basic - Location page.
  2. Open the Location Type drop-down list.
  3. Select Fixed.

    4. With this option, the location of the sensor is defined using a fixed displacement vector with respect to the parent object’s body frame.

  4. Set the following options:
    5. Option Value
    X 75 ft
    Z 75 ft
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Targeting the test missile

Next, target the test missile by updating the sensor's Pointing properties to determine how the sensor is aimed with respect to its parent object.

  1. Select the Basic - Pointing page.
  2. Open the Pointing Type drop-down list.
  3. Select Targeted.
  4. Use the Default Receive Track mode in the Targeted panel.

    5. The Track Mode specifies how you want to orient the antenna. By default, this is set to Receive; this orients the antenna slightly "behind" the current location of the other object. The STK application computes the appropriate amount by which to lead or trail based on the light time delay. Access computations including the computation of targeting times are performed based on the sensor being the receiver of the signal.

  5. Select Test_Missile () in the Available Targets list.
  6. Move () Test_Missile () to the Assigned Targets list.
  7. Click OK to confirm your changes and to close the Properties Browser.

Viewing the targeted antenna in the 3D Graphics window

View the ship and its sensor in the 3D Graphics window.

  1. Zoom To Ship ().
  2. Click Start () on the Animation toolbar to animate the scenario.

    3. Sensor Targeting Test Missile

  3. Look at Antenna_Motor's () location on the ship.

    4. When Antenna_Motor is able to access Test_Missile, the sensor field of view will be visible.

  4. Click Reset () when you are finished.

Modeling the test ship's receiver

The ship's on-board communications equipment will receive telemetry transmissions from the missile.

Inserting a Receiver object

Use a Receiver object to model the characteristics of the receiver, the antenna it uses, and the environment in which it operates.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Receiver () object using the Insert Default () method.
  3. Select Antenna_Motor () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Receiver1 () Ship_Rx.

Using a Complex Receiver model

Use a Complex Receiver 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. Open Ship_Rx's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Receiver Model Component Selector ().
  4. Select Complex Receiver Model () in the Receiver Models list when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Leave the Auto Track check box selected.

    7. The Auto Track option allows a receiver to track and lock onto the transmitter's carrier frequency with which it is currently linking, including any Doppler shift.

  7. Click Apply to confirm your changes and to keep the Properties Browser open.

Defining the receiver's antenna specifications

The receiver uses a Helix antenna pattern, which models a standard helical antenna.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select Helix () in the Antenna Models list when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Set the following antenna specifications:
    7. Option Value
    Design Frequency 2.5 GHz
    Diameter 0.9 m
    Turn Spacing 1 mm
    Number of Turns 3
  7. Click Apply to confirm your changes and to keep the Properties Browser open.

Visualizing the receiver's antenna pattern

The 3D Graphics Attributes page for a Receiver object allows you to visualize its antenna pattern.

  1. Select the 3D Graphics - Attributes page.
  2. Select the Show Volume check box in the Volume Graphics panel.
  3. Enter 0.5 km in the Gain Scale (per dB) field.
  4. Select the Set Azimuth and elevation resolution together check box in the Patten panel.
  5. Enter 1 deg in the Resolution field in the Azimuth panel.

Adding gain coloring

Use the Explicit Levels Method to define individual antenna gain levels and specify how colors will be added to show antenna gain.

  1. Open the Method drop-down list in the Gain Coloring panel.
  2. Select Explicit Levels.
  3. Select the Relative to Maximum check box in the Gain Coloring panel.

    4. When selected, the antenna gain level values are assumed to be relative to the maximum value.

  4. Set the following options in the Level Adding panel:
    5. Option Value
    Add Method Start, Stop, Step
    Start -70
    Stop 0
    Step 10
  5. Click Add Levels.
  6. Click Apply to confirm your changes and to keep the Properties Browser open.

Viewing the antenna pattern in the 3D Graphics window

With your gain antenna graphics configured, view the pattern in the 3D Graphics window.

  1. Bring the 3D Graphics Window to the front.
  2. Click Start () on the Animation toolbar to animate the scenario.

    3. Helix Antenna Pattern

    When Antenna_Motor accesses Test_Missile, the antenna pattern will be visible. Your antenna pattern colors might not look the same as the colors in the image above. You may want to zoom out a bit to get a better view of the entirety of the pattern.

  3. Click Reset () when you are finished.
  4. Return to Ship_Rx's () Properties ().
  5. Clear the Show Volume check box in the Volume Graphics panel.
  6. Click OK to confirm your change and to close the Properties Browser.

Analyzing the telemetry downlink's link budget

The missile will transmit telemetry data to the ship during its flight. Create a simple link budget to calculate the bit error rate (BER), which reflects of how often errors occur in the transmission of digital data. You can compute a simple link budget using the Access tool. The Access tool's preinstalled Link Budget report includes all the basic link parameters associated with the selected receiver or transmitter. It gives you the signal strength and quality of the link received at the ship from the missile. Obviously, you want a low BER value, because that means you have fewer errors over time. For the purposes of this analysis, a Bit Error Rate of 1.000000e-09 or lower is acceptable.

  1. Right-click on Ship_Rx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Expand () Test_Missile () in the Associated Objects List when the Access tool opens.
  4. Select Missile_Tx ().
  5. Click .
  6. Click Link Budget. . . in the Reports panel.
  7. Scroll to the right until you find the BER column when the Link Budget report opens.
  8. Scroll down through the column.

    9. For the most part, you have good reception from the missile to the ship. As the missile gets further away from the ship, the bit error rate increases.

  9. When finished, close the Link Budget report.
  10. Keep the Access tool open.

Inserting the interfering satellites

Recall that the missile is transmitting in the S band. This is near a frequency on which multiple SDARS satellites are providing XM satellite radio service. Insert the operational XM radio SDARS satellites using the Standard Object Database.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Satellite () object using the From Standard Object Database () method.
  3. Clear the Data Sources: Local check box when the Search Standard Object Data dialog box opens.
  4. Enter SXM in the Name or ID field.
  5. Open the Owner drop-down list.
  6. Select United States.
  7. Click Search.
  8. Select all SXM satellites whose Operational Status is Operational in the Results list.
  9. Click Insert.
  10. When all the Satellite () objects have propagated, click Close to close the Search Standard Object Data dialog box.

Modeling the interfering satellites' transmitters

The satellites broadcast XM radio in the S band. Model one satellite's transmitter first, then reuse it with for the other satellites so you don't have to model each individually.

Inserting a new Transmitter object

Attach a transmitter to one of the SXM satellites.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Transmitter () object using the Insert Default () method.
  3. Select one of the SXM Satellite () objects when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to Select Object dialog box.

Using a Medium Transmitter model

As with the missile's transmitter, use a Medium Transmitter model in your analysis.

  1. Open Transmitter2's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Click the Transmitter Model Component Selector ().
  4. Select Medium Transmitter Model () in the Transmitter Models list when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Select the Model Specs tab.
  7. Set the following transmitter specifications:
    8. Option Value
    Frequency 2.3347 GHz
    Power 13300 W
    Gain 40 dB
    Data Rate 0.048 Mb/Sec
  8. Click Apply to confirm your changes and to keep the Properties Browser open.

Updating the modulation options

The satellite transmitters use quadrature phase shift keying (QPSK) to cover large regions with low population densities.

  1. Select the Modulator tab.
  2. Open the Name drop-down list.
  3. Select QPSK.
  4. Select the Use Signal PSD check box.
  5. Click OK to confirm your selections and to close the Properties Browser.

Reusing and renaming the satellite transmitters

All the SXM satellites will use the same transmitter type and specifications. You can reuse Transmitter2 (copy and paste) which is a quick way to create a new object having identical properties to an object already existing in the scenario.

  1. Select Transmitter2 () in the Object Browser.
  2. Click Copy () on the Object Browser toolbar.
  3. Select another SXM satellite () in the Object Browser.
  4. Click Paste () on the Object Browser toolbar.
  5. Repeat the process for the remaining SXM Satellites.
  6. Rename the transmitters [Satellite Common Name]_Tx.

    7. For example, for the satellite SXM-10_64290 (), rename its transmitter SXM-10_Tx ().

Checking for interference

There are several methods through which you can determine the impact of interference on a system. For more complex systems, you can use a Comm System to model dynamically configured communications links between constellations of transmitters and receivers. However, for less complex systems, like the one in this scenario, you can compute interference effects directly in a Receiver object.

Adding interference sources to the receiver

Add the satellite transmitters as interference sources to your RF receiver through its properties. Then, you can assess their impact on the performance of the receiver.

  1. Open Ship_Rx's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Select the Interference tab.
  4. Select the Use check box.
  5. Select Transmitter () in the Selection Filter panel.
  6. Move () all of the transmitters from the Available Emitters list to the Assigned Emitters list.

    7. Only qualified assets will appear in the Available Emitters list, including Transmitter objects configured with one of the RF transmitter models (no laser models) and Radar objects configured with either the Monostatic or Bistatic Transmitter Radar systems.

  7. Select Test_Missile/Mssile_Tx () in the Assigned Emitters list.
  8. Remove () Test_Missile/Mssile_Tx () from the Assigned Emitters list.
  9. Click Apply to confirm your changes and to keep the Properties Browser open.

Determining the impact of interference with a Link Budget - Interference report

Generate a Link Budget - Interference report to determine if the SDARS satellites will interfere with the telemetry data. A Link Budget - Interference report shows key link budget parameters (EIRP, Frequency, RIP, Flux Density, g/T, C/No, Bandwidth, C/N, Eb/No, and BER.) and also reports key link performance parameters under the presence of interfering signals, such as C/(No+Io), C/(N+I), C/I, Eb/(No+Io), and BER+I.

  1. Return to the Access tool.
  2. Click Report & Graph Manager....
  3. Select the Link Budget - Interference () report style, located in the Installed Styles () folder in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate....
  5. Click Show Step Value when the report opens.
  6. Enter 1 sec in the Step field.
  7. Select the Enter key.
  8. Locate the BER and BER+I columns.

    9. BER+I is the Bit Error Rate in the presence of Interference.

  9. Scroll down through the report and compare the columns.

    10. Link Budget - Interference report

    Your report may look different than the one show above. In this analysis, you require a BER of 1.000000e-09 or lower. You can see that the XM satellite transmitters will interfere with the telemetry data being transmitted from the test missile to the ship. Note the time(s) at which interference raises the BER+I above 1.000000e-09.

  10. Leave the Link Budget - Interference report open.

Mitigating interference with a spectrum filter

Having determined that the SDARS 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 SDARS satellites' 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.

Using a Butterworth filter

Use a Butterworth filter. A 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 can be adjusted, if required.

  1. Return to Ship_Rx's () Properties ().
  2. Select the Filter tab.
  3. Select the Use check box in the Filter Model panel.
  4. Ensure Butterworth is selected for the Filter Model.
  5. Enter 5 MHz in the Cut-off Frequency field.
  6. Click OK to confirm your changes and to close the Properties Browser.

Recomputing the Link Budget - Interference report

Check the effect of filtering on the signal quality.

  1. Bring the Link Budget - Interference report the front.
  2. Click Refresh (F5) () in the report's toolbar.
  3. Review the report.

    4. Notice that BER+I using filtering shows improvement in link performance over BER+I without filtering. You should also see approximately 0.5 dB of improvement in the energy per bit to noise-plus-interference ratio (Eb/(No + Io)) with the Butterworth filter. Using a 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.

  4. When finished, close the Link Budget - Interference report.
  5. Click Close to close the Report & Graph Manager.
  6. Clear the check box for Antenna_Motor () in the Object Browser.

    7. This will remove it visually from your scenario.

  7. Bring the Access tool to the front.
  8. Click Remove All Accesses ().
  9. Click Close to close the Access tool.
  10. Save () your scenario.

Modeling the ship's radar

The second phase of the test determines for how long the ship's radar can track the test missile. The radar tracks the missile by sending pulses to determine probability of detection (PDET). The radar continues to send pulses until it meets an assigned signal-to-noise ratio (SNR) goal. At the end of sending the pulses, if none of them hit the missile and return, then the radar did not detect the missile.

The Radar capability implements a Swerling detection model. The probability of detection is a function of the per pulse SNR, the number of pulses integrated, the probability of false alarm, and the radar cross-section (RCS) fluctuation type, which is taken from the target RCS properties. You will base test on achieving an integrated PDET value of 0.800000 or higher, 1.000000 being the highest value.

Inserting a Radar object

A Radar object models the characteristics of a radar system and its environment. Attach a Radar object to the ship.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Radar () object using the Insert Default () method.
  3. Select Ship () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename Radar1 () Ship_Radar.

Setting the radar's mode

The ship is equipped with a Search/Track (S/T) radar, which detects and tracks point targets.

  1. Open Ship_Radar's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Leave the Radar System set to Monostatic.

    4. A Monostatic radar uses a common antenna for both transmitting and receiving.

  4. Select the Mode tab.
  5. Ensure the Radar Monostatic Mode is set to Search Track.
  6. Select the Waveform sub-tab.
  7. Leave the Waveform set to Fixed PRF.

    8. The waveform in your system will use a fixed pulse repetition frequency (PRF). The PRF is the number of pulses of a repeating signal in a specific time unit. After producing a brief transmission pulse, the transmitter turns off in order for the receiver to hear the reflections of that signal off of targets.

  8. Select the Pulse Definition sub-tab on the Waveform sub-tab.
  9. Enter 880 nsec in the Pulse Width field.

    10. This is the width of the transmitted pulse in nanoseconds, which is equivalent to 8.8e-07 sec.

  10. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the goal signal-to-noise ratio

Radar systems often use multiple pulse integration, which is the process of summing all the radar pulses, to improve detection. This helps increase the SNR. For a Fixed PRF radar, select either an integration analysis based on the desired signal-to-noise ratio (Goal SNR) or a fixed number of pulses (Fixed Pulse Number).

  1. Select the Pulse Integration sub-tab on the Waveform sub-tab.
  2. Leave the analysis mode set to Goal SNR.
  3. Enter 20 dB in the SNR field.
  4. Leave the Maximum Pulses set to the default value of 512.
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Configuring the radar's antenna

The ship's tracking radar is similar to an airport surveillance radar, which spins, covering a 360-degree field of view. Model the radar's antenna with an External Antenna Pattern component, which is used for files arranged in a format used by the STK application.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select External Antenna Pattern () when the Select Component dialog box opens.
  5. Click OK to confirm your selection and to close the Select Component dialog box.
  6. Enter 2.8 GHz in the Design Frequency field.

Selecting the external pattern file

Use an external antenna pattern file, which contains user-defined data, to model the field of view of this type of radar.

  1. Click the External Filename ellipsis ().
  2. Browse to <Install Dir>\Data\Resources\stktraining\samples when the Select File dialog box opens.
  3. Select ASR9Low.pattern.

    4. The ASR9Low.pattern file uses a Symmetric antenna pattern format. You can open ASR9Low.pattern using a text editor such as Notepad to view the file. Use this type for antenna patterns that are symmetric about the boresight of the antenna, where the gain value does not change as a function of phi (azimuth). Inside the Pattern file are several keywords that identify the type of antenna pattern as well as other pertinent information for importing the pattern.

  4. Click Open to select the antenna pattern file and to close the Select File dialog box.
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the radar antenna's location

The radar is located at the top of the ship's mast. Adjust the Radar antenna's Orientation properties to place it at the correct height.

  1. Select the Orientation sub-tab.
  2. Set the following values in the Position Offset panel:
    3. Option Value
    X 37 ft
    Z 120 ft
  3. Click Apply to confirm your changes and to keep the Properties Browser open.

Setting the radar transmitter specifications

Model the specifications of the radar transmitter.

  1. Select the Transmitter tab.
  2. Select the Specs sub-tab.
  3. Select the Frequency option.
  4. Set the following transmitter specifications:
    5. Option Value
    Frequency 2.8 GHz
    Power 11 GW
  5. Click Apply to confirm your changes and to keep the Properties Browser open.

Changing the radar receiver LNA gain

Add the value for the gain introduced by the Low Noise Amplifier (LNA) by updating the radar receiver properties.

  1. Select the Receiver tab.
  2. Select the Specs sub-tab.
  3. Enter 25 dB in the LNA Gain field.
  4. Click OK to confirm your changes and to close the Properties Browser.

Defining the missile's radar cross section

The Radar capability enables you to specify an important property of a potential radar target: its radar cross section (RCS). To design a radar system, it is essential to be able to describe the target's echo, which is a function of its size, shape, and orientation. RCS is the projected area of a metal sphere that would return the same echo signal as the target if it were substituted for the target. The signal return from a point target is inversely proportional to the fourth power of target range and directly proportional to the target's radar cross section. Real targets have widely differing radar cross sections from different aspect angles.

You can define the missile's RCS using an external RCS file. External RCS files can contain real-valued pattern data or complex-valued pattern data.

  1. Open Test_Missile's () Properties ().
  2. Select the RF - Radar Cross Section page when the Properties Browser opens.
  3. Clear the Inherit check box.
  4. Open the Compute Type drop-down list in the Band Properties panel.
  5. Select External File.
  6. Click the Filename ellipsis ().
  7. Browse to <Install Dir>\Data\Resources\stktraining\samples when the Select File dialog box opens.
  8. Select the Basic_Missile_mono.rcs file.

    9. The Basic_Missile_mono.rcs file uses the RealSymmetric (*.rcs) file format. You can open Basic_Missile_mono.rcs using a text editor such as Notepad to view the file.

  9. Click Open to select the RCS file and to close the Select File dialog box.
  10. Click OK to confirm your changes and to close the Properties Browser.

Computing access

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

  1. Right-click on Ship_Radar () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select Test_Missile () in the Associated Object list when the Access tool opens.
  4. Click .
  5. Click Report & Graph Manager....

Creating a custom report

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

Creating a new report style

Create a new report style for your custom report.

  1. Select the My Styles () folder in the Styles panel list, when the Report & Graph Manager opens.
  2. Click Create new report style () on the Styles toolbar.
  3. Rename the report AER and Search Track Data.
  4. Select the Enter key.

Adding data providers

Define the contents of your new report style by selecting the data providers you wish to use in the report content properties.

  1. Select the Content - page when the Properties Browser opens.
  2. Expand () the AER Data () data provider in the Data Providers list.

    3. 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.

  3. Expand () the BodyFixed () data provider group.
  4. Move () the following data provider elements to the Report Contents list in the order shown:
    • Time ()
    • Azimuth ()
    • Elevation ()
    • Range ()
  5. Expand () the Radar SearchTrack () data provider.

    6. The Radar SearchTrack data provider reports the dynamic Search Track mode radar performance data between the radar system and the selected target.

  6. Move () the following data provider elements to the Report Contents section in the order shown:
    • S/T Integrated SNR () — signal quality of the return from the radar
    • S/T Integrated PDet () — probability that the missile is detected
    • S/T Pulses Integrated () — number of pulses needed to detect the missile
  7. Expand () the Radar RCS () data provider.

    8. The Radar RCS data provider reports on radar cross section settings.

  8. Move () the RCS data provider element () to the Report Contents list.
  9. Click OK to confirm your changes and to close the Properties Browser.

Setting the time period

Now that the data providers have been defined, you can specify the time period during which data are reported.

  1. Select the Specify Time Properties option in the Time Properties panel.
  2. Set the following time options:
    3. Option Value
    Start [Date] 16:00:00.000 UTCG
    Stop [Date] 16:00:20.000 UTCG
  3. Select the Use step size/ time bound option.
  4. Enter 0.1 sec in the Step size field.
  5. Click Generate. . ..

AER and Search Track Data Report

Your report will look different than the one shown above, which has been modified to limit the start time for illustration purposes. Notice how long you can track the test missile basing it on an S/T Integrated PDet value of 0.8 or higher — approximately 16 seconds. Also note the change in azimuth, elevation, and range as the missile travels along its arc.

Saving your work

Clean up your workspace and save your work.

  1. Close any open reports, tools, and the Report & Graph Manager.
  2. Save () your work.

Summary

You determined that a portion of test missile's telemetry data was interfered with by the satellite radio transmissions. By using a Butterworth filter, you were able to largely mitigate the interference. Using an external antenna pattern, you model a specific shipboard radar that functioned similar to an air surveillance radar. You applied an external radar cross section file to the test missile, which modeled a specific missile type. By creating a custom report, you determined that the ship's radar was able to track the test missile for approximately 16 seconds of its flight.

On your own

Change the 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 further mitigate the interference in the link budget. Keep the current settings, but change the test missile's flight path (that is, the impact point, apogee altitude, etc.) to evaluate the effects.