Analyzer: Radar Analysis

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.

Capabilities Covered

This lesson covers the following capabilities:

  • STK Core
  • STK Analyzer
  • Radar

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.

Analyzer

Analyzer is integrated into the STK workflow to help you automate and analyze STK trade studies in order to better understand the design of your system. For purposes of this tutorial, Analyzer will be used to:

  • Parametrically explore the STK design space in order to analyze your radar tracking scenario.
  • Perform parameter studies that vary an input variable through a range of values and plot one or more output variables.

Launch Vehicle Tracking Exercise

A Launch Vehicle Object will be launched and burns out in ten minutes. A radar site near the launch pad will track the launch vehicle using a phased array antenna.

The goal of this scenario is to study the impact of two variables on the performance of a radar used to track the launch vehicle.

You will run several parametric studies and a carpet plot to gain a better understanding of how these parameters impact performance. In this case, performance will be measured by integrated probability of detection (PDet). You would like for the average integrated PDet to be close to 0.5 to ensure that the radar can track the launch vehicle. Finally, you will use the Optimization Tool to determine the best parameter combination that will provide the highest probability of tracking the launch vehicle. The input parameters you will be studying are:

  • Wavelength
  • Power

You will use base values of 0.1 m for wavelength and 40 dBW for power.

Video Guidance

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

Using a starter scenario

To speed things up and have you to focus on the portion of this exercise that teaches you Analyzer, a partially created scenario has been provided for you.

Loading the starter scenario

The STK scenario (VDF) used with this tutorial is located in the STK Data Federate (SDF). To open the scenario:

  1. Ensure that the Welcome dialog box is visible in the STK Workspace.
  2. Click Open a Scenario.
  3. Select STK Data Federate from the Location drop-down arrow.
  4. Go to the Sites/AGI/documentlibrary/STK 12/Starter Tutorials folder.

Open the VDF

  1. Select Analyzer_RadarAnalysis.vdf.
  2. Click Open .

Saving the starter scenario as an SC file

When you open the scenario, STK will create a folder with the same name as the scenario in the default user folder (C:\Documents\STK 12, for example). STK will not save the scenario automatically. When you choose save a scenario, STK will default to saving it in the format in which it originated. Therefore, if you open a VDF, the default save format will be a VDF. The same is true for a scenario file (*.sc). To save the VDF as an SC file, change the file format using the Save As procedure:

  1. Open the File menu and select Save As...
  2. Click to browse to your user location.
  3. Open the folder with the same name as the scenario.
  4. Change "Save as type" to Scenario Files (*.sc) and click Save .
  5. Click Yes to confirm.

3D Graphics Window

External Radar Cross Section Files

While setting up and constraining a radar system, Radar allows 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 defined as the projected area of a metal sphere that would return the same echo signal as the target if it were substituted for the target.

You will be using a custom radar cross section file to define the RCS of the launch vehicle. A file containing this data is included with the scenario. Load this file in the launch vehicle's properties.

  1. In the Object Browser, open LaunchVehicle's properties.
  2. Browse to the RF - Radar Cross Section page.
  3. At the top of the page, clear the Inherit check box.
  4. In the Compute Type: field, select External File.
  5. Click the Filename: ... button.
  6. Select the file Basic_missile_mono.rcs and click Open .

    7. If you click the ... button and you're directed to a directory other than the scenario folder, browse to the scenario directory (e.g. C:\Users\<user>\Documents\STK 12\Analyzer_Radar_Analysis) and select the .rcs file.
  7. Click OK .

Compute Access

You will use Analyzer to perform studies on integrated PDet. First, you’ll need to calculate access between the radar and launch vehicle.

  1. In the Object Browser, right-click PhasedArrayRadar and select Access... .
  2. When the Access window opens, select LaunchVehicle.
  3. Click Compute.
  4. Click the Report & Graph Manager... button.
  5. When the Report & Graph Manager window opens, in the Styles List, select Radar SearchTrack report.
  6. Click Generate... .

    7. Radar Search Track Results

    Note the S/T Integrated PDet value. This value will be accessible in Analyzer as an output variable. The PDet ranges from 0.0001 to 1.0000 with the majority being below the required value of > 0.5000. By varying each of the parameter inputs, you’ll determine which values are necessary to meet the requirement. You’ll also see how a carpet plot will allow you to change more than one input at once and determine what combinations of two inputs can achieve the minimum requirement. The final optimization will provide the best combination of parameters to track the launch vehicle.

  7. Close the report, the Report & Graph Manager and the Access Tool.

Analyzer Layout

Use the Analyzer Main Form to configure input/output variables available for further analysis. You can first select an object in the scenario tree on the left. When an object is selected, all possible input variable candidates are listed under the STK Property Variables and Active Constraints tab. All output variable candidates are listed under the Data Providers Variables tab, Object Coverage tab, DeckAccess tab or MissileModelingTools tab.

Wavelength Study

The first parameter you will examine is the transmitter's wavelength. You need to select input and output variables from the main Analyzer window to pass to the Parametric Study tool.

Select the input variable.

  1. Click the Analyzer button on the Analyzer Tool Bar.

    2. Analyzer Tool Bar Analyzer Icon

    Another way of opening Analyzer is to go to the Object Browser, right click on the scenario object (or any object), select the object's Plugins, and click Analyzer.
  2. When Analyzer is open, in the STK Variables list, expand RadarSite.
  3. Select PhasedArrayRadar.
  4. In the STK Property Variables field, expand SystemMonostatic, Transmitter, and Specs.
  5. Under Specs, double-click Wavelength. This moves Wavelength to the Analyzer Variables field as an input.

Select the output variables.

  1. In the STK Variables list, expand Access and select Facility-RadarSite-Radar_PhasedArrayRadar-to-LaunchVehicle-LaunchVehicle.
  2. At the bottom of the Data Providers list, enable Show all data providers.

    3. Show All Data Providers

  3. In the Data Providers field, expand Radar SearchTrack and then S/T Integrated PDet.
  4. Move Mean into the Analyzer Variables field.

Parametric Study Tool

The Parametric Study Tool runs a Scenario through a sweep of values for some input variable. The resulting data can be plotted to view trends.

  1. In the Analyzer tool bar, select Parametric Study.

    2. Parametric Study Icon

    Analyzer builds a parametric representation of the currently loaded Scenario. This representation is viewed in the Component Tree displayed on the left side of each trade study tool.

  2. When the Parametric Study opens, in the Component Tree, using your left mouse button, drag Wavelength to the Design Variable field on the right.

    3. Design Variable

  3. Set the following Design Variables:
    4. Option Value
    starting value: .1
    ending value: 10
    number of samples: 51
    step size: .2
  4. In the Component Tree, using your left mouse button, drag Mean to the Responses field on the right.
  5. In the lower right hand corner of the Parametric Study Tool, click Run... .

Data Explorer

The Data Explorer is a tool used by Trade Study tools to display data while they are being collected from STK. While data is being collected, the Data Explorer displays a progress meter, a halt button, and the data.

Table Page

The Table page displays trade study data in a tabular form. It is the default window that is present for all trade studies. Cells are shaded differently depending on the associated variable's state. Input variables are shown with green text, valid values are displayed with black text, invalid values are displayed with gray text, and modified values are displayed with blue text. From the table it is possible to view and edit all values in your trade study and even to add and remove whole runs.

Table Page

The results of your trade studies will show mean values throughout.

Toolbar

Once the trade study is complete and all data has been collected, the Data Explorer toolbar becomes active.

Data Explorer Tool Bar

Plot Types

Some trade study tools will automatically launch a default plot window when the trade study runs. Other plots can be created from the Add View drop down menu.

Views

There are multiple views that can be selected to visualize the data seen on the Table Page. You can choose views by clicking on Add View. You can build custom views or switch to Legacy Views.

  1. Close the 2D Scatter Plot that opened when you ran the trade study.
  2. On the Table Page tool bar, expand Add View and select 2D Line Plot.

Axes

Use the Axes tab to set options for the axes.

  1. Click Axes.
  2. Select the Ticks tab.
  3. Change the Max # value to 40.
  4. Click on the plot to close the Axes menu.

    5. Wavelength 2D Line Plot

    As the transmitter's wavelength increases (the frequency becomes lower), the average PDET increases. Between a wavelength of three and six, this increase tapers off.

  5. Close the 2D Line Plot and the Table Page.
  6. When prompted to save, click No .
  7. Close the Parametric Study Tool.
  8. Return to Analyzer.

Power Study

Wavelength is not the only transmitter parameter that will impact your tracking. Power also has an impact. To determine how much, run another Parametric Study.

Select the input variable.

  1. In the STK Variables list, expand RadarSite.
  2. Select PhasedArrayRadar.
  3. In the STK Property Variables field, expand SystemMonostatic, Transmitter, and Specs.
  4. Under Specs, double-click Power. This moves Power to the Analyzer Variables field as an input.
  5. In the Analyzer tool bar, click Parametric Study.
  6. Click the Value field for the Wavelength and change it to 10 m.
  7. In the Component Tree, using your left mouse button, drag Power to the Design Variable field on the right.
  8. Set the following Design Variables:
    9. Option Value
    starting value: 100
    ending value: 14000
    number of samples: 15
    step size: 1000
  9. In the Component Tree, using your left mouse button, drag Mean to the Responses field on the right.
  10. In the lower right hand corner of the Parametric Study Tool, click Run... .

View

  1. Close the 2D Scatter Plot that opened when you ran the trade study.
  2. On the Table Page tool bar, expand Add View and select the 2D Line Plot.

Axes

  1. Click Axes.
  2. Select the Ticks tab.
  3. Change the Axes Ticks to twenty (20).

    4. Power Change

    Power shows a steady increase of Mean Integrated PDET between 4 and 8 kW.

  4. Close the 2D Line Plot and the Table Page.
  5. When prompted to save, click No .
  6. Close the Parametric Study Tool.
  7. Return to Analyzer.

Determine if Wavelength and Power Impact One Another

You have determined that wavelength and power have significant impacts on Integrated PDET. This leads to the following question:

How do wavelength and power affect one another?

You can answer the question by performing a 2-dimensional parametric study called a Carpet Plot.

Carpet Plot Tool

A Carpet Plot is a means of displaying data dependent on two variables in a format that makes interpretation easier than normal multiple curve plots. A Carpet Plot can be thought of as a multi-dimensional Parametric Study.

  1. In the Analyzer tool bar select Carpet Plot.

    2. Carpet Plot Study Icon

    Setting the design variables is similar to using the Parametric Study Tool except you now have two variables instead of one.

  2. In the Component Tree, using your left mouse button, drag Wavelength to the first Design Variable field on the right and Power to the second Design Variable field.
  3. Set the following Wavelength Design Variables:
    4. Option Value
    From .1
    To 10
    Num Steps 11
    Step Size 1
  4. Set the following Power Design Variables:
    5. Option Value
    From 2000
    To 14000
    Num Steps 13
    Step Size 1000

    If you are wondering why this tutorial uses large step sizes, it's due to keeping the tutorial time under an hour. These settings will require a total of 143 runs to obtain every variable combination. On your own, you can set the Wavelength and Power to change at smaller step sizes to make the trade study more realistic. Be patient. Depending on your settings, you could end up running hundreds of runs.

  5. In the Component Tree, using your left mouse button, drag Mean to the Responses field on the right.
  6. In the lower right hand corner of the Carpet Plot Tool, click Run... .

    7. Carpet Plot

    Using the Carpet Plot, you can find different combinations of wavelength and power that allow you to maintain an Mean Integrated PDET of .5 or higher.

  7. Close the Carpet Plot and the Table Page.
  8. When prompted to save, click No .
  9. Close the Carpet Plot Tool.
  10. Return to Analyzer.

Optimize Transmitter Parameters

You now know that transmitter parameters have an impact on Integrated PDET. In order to optimize these parameters, you can either guess at values, or employ an optimization tool. Although you can clearly see trends from the previous studies, guessing at values will be difficult because you are dealing with multiple parameters at the same time.

To solve more complex problems, an optimization tool can be a very useful guide. An optimizer is an automated tool that makes mathematical calculations about a design problem and incrementally attempts to find an optimal solution. The algorithm you will employ here is an optimizer. The selected algorithm will compute derivatives about an initial point in the design space and compute a search direction. This process will repeat until no more progress can be achieved on the objective function.

An optimizer will be used in this problem to minimize the power requirement for the transmitter while maintaining an average Integrated PDET of ~ 0.5.

Optimization Tool

The Optimization Tool is a collection of optimization algorithms that can be used within Analyzer. Currently over 30 algorithms are available including gradient based optimizers, genetic algorithms, multi-objective algorithms, and other heuristic search methods (see Algorithm Comparison Chart). A common graphical user interface is provided to define optimization problems. The objective is to minimize the value for power and maximize the Mean Integrated PDET by changing wavelength and power.

  1. In the Analyzer tool bar select the Optimization Tool.

    2. Optimization Tool Icon

    The objective is to minimize the value for power by changing wavelength and power all while maintaining an Mean Integrated PDET as close to 0.5 as possible. It's probable that you won't meet your goal due to radar system limitations, but you can still get close.

  2. In the Component Tree, using your left mouse button, drag Power to the Objective field on the right.
  3. Set Goal to Minimize.
  4. In the Component Tree, using your left mouse button, drag Mean to the Objective field on the right.
  5. Set Goal to Maximize.
  6. In the Component Tree, using your left mouse button, drag Mean to the Constraint field on the right.
  7. Set the Lower Bound to 0.5 and the Upper Bound to 1.0.
  8. In the Component Tree, using your left mouse button, drag Wavelength and Power to the Design Variables field on the right.
  9. In the Design Variables field, change the Wavelength Start Value (Explicit Value) to one (1). This value has to be at least or greater than the lower bound value.
  10. Change the Power Start Value (Explicit Value) to 2000. This value has to be at least or greater than the lower bound value.
  11. Continue making the following changes:
    12. Option Lower Bound Upper Bound
    Wavelength 1 10
    Power 2000 14000
  12. Set Algorithm to Darwin Algorithm.

    13. Darwin is a genetic search algorithm developed specifically for solving engineering optimization problems. Darwin is capable of handling discrete variables, continuous variables, and any number of constraints. Because Darwin does not require gradient information, it is able to effectively search non-linear and noisy design spaces.

  13. In the lower right hand corner of the Optimization Tool, click Run .

    14. The optimizer will display a history of steps as it progresses. By default only the objective definition will be displayed.

    The above process can be repeated to add plots for frequency and data rate. This study will take a long time to complete.

  14. Close the 2D Scatter Plot.
  15. When the optimization study is complete, the View Output button on the Optimization Tool panel will contain the convergence history of the process. Select the Best Design tab which contain the optimized values. These values are also displayed in the Value column for the design variables in the Optimization Tool. See the images below.

    16. Optimization Values

    You are able to maintain an average PDET above 0.5. The Optimization Tool got you within the bounds.

  16. Click the Sync to STK button to push these parameters to the scenario.

When You Finish

  1. Close the Table Page, the Optimization Tool, and Analyzer.
  2. Save your work.
  3. Close the scenario.
  4. Close STK.