Part 12: Introduction to Radar

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training by contacting AGI Support at support@agi.com or 1-800-924-7244.

Note: 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
  • Radar

Problem Statement

Engineers and operators need to determine how various radar settings will affect its ability to track different sized targets.

They want to know how the following settings affect a radar's ability to track multiple target types:

  • Radar Cross Section
  • Pulse Repetition Frequency
  • Gain
  • Pulse integration

Solution

Use STK Pro and STK's Radar capability to:

  1. Create an airfield radar site
  2. Model an airport surveillance radar
  3. Build a monostatic radar
  4. Test various settings against multiple targets
  5. Determine probability of detection

What you will learn

Upon completion of this tutorial, you will understand:

  • Radar Cross Sections
  • Monostatic Radars and their settings
  • Radar Data Providers

Video Guidance

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

Create a new scenario

Create a new scenario.

  1. Launch STK ().
  2. Click Create a Scenario () in the Welcome to STK window.
  3. Enter the following in the New Scenario Wizard:
    4. Option Value
    Name: STK_Radar
    Location: Default
    Start: 1 Oct 2020 03:00:00.000 UTCG
    Stop: +30 min
  4. When finished, click OK.
  5. When the scenario loads, click Save (). A folder with the same name as your scenario is created for you in the location specified above.
  6. Verify the scenario name and location in the Save As window.
  7. Click Save.

Save () often!

Turn Off Terrain Server

This is an introduction to Radar. Terrain will not be used in this analysis.

  1. Open STK_Radar's () properties ().
  2. Select the Basic - Terrain page.
  3. Clear Use terrain server for analysis.
  4. Click OK to accept the changes and close the Properties Browser.

Turn On Label Declutter

Turn on Label Declutter to reposition object labels so they do not obstruct one another while in close proximity.

  1. Open the 3D Graphics Window's properties ().
  2. Select the Details page.
  3. Select Enable for Label Declutter.
  4. Click OK.

Insert the Target Aircraft

Insert an Aircraft () object. We will use the aircraft to analyze the airfield surveillance radar.

  1. Select Aircraft () in the Insert STK Objects tool.
  2. Select the Insert Default method.
  3. Click Insert....
  4. Rename the Aircraft () Target_Acft.

Create the Target Aircraft's Route

Create Target_Acft's () route, then modify it's altitude and speed.

  1. Open Target_Acft's () properties ().
  2. Select the Basic - Route page.
  3. Click Insert Point two times.
  4. Set the following:
    5. Waypoint Latitude Longitude
    One 37 deg 139.7 deg
    Two 34 deg 139.1 deg
  5. Click Set All....
  6. Select Altitude: and Speed: in the Set All Grid Values window.
  7. Set the following:
    8. Option Value
    Altitude: 25000 ft
    Speed: 330 mi/hr
  8. Click OK to close the Set All Grid Values window.
  9. Click Apply to accept the changes and keep the Properties Browser open.

Specify the Radar Cross Section

Before 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). Use the RCS of a popular four engined transport turboprop aircraft.

  1. Select the RF - Radar Cross Section page.
  2. At the top of the page, clear Inherit. This allows you to set the RCS settings for the Aircraft () instead of inheriting the settings from the Scenario () object.
  3. Set the Constant RCS Value: to 19 dBsm (decibels referenced to a square meter).

    4. Ideally, you would want to use an Aspect Dependent RCS file. Since you don't have one, you will use a constant value. The constant value we set is the RCS of a sphere that radiates isotropically.

  4. Click Apply.

Display Radar Cross Section Graphics

The 3D Graphics RCS page allows you to control the 3D display of Radar Cross Section contour lines.

  1. Select the 3D Graphics - Radar Cross Section page.
  2. Select Show Volume in the Volume Graphics section.
  3. Click OK.
  4. Bring the 3D Graphics window to the front.
  5. Right-click on Target_Acft () in the Object Browser.
  6. Select Zoom To.
  7. Use your mouse to zoom out until you can see the RCS sphere.

Radar Cross Section Sphere

Insert the Radar Site

Use a Place () object as the radar site location.

  1. Select Place () in the Insert STK Objects tool.
  2. Select the Insert Default method.
  3. Click Insert....
  4. Rename the Place () Radar_Site.

Define the Radar Site's Location

Define the location of Radar_Site (), and raise its height above ground 50 ft to model the radar antenna height.

  1. Open Radar_Site's () properties ().
  2. Select the Basic - Position page.
  3. Set the following:
    4. Option Value
    Latitude: 35.7517 deg
    Longitude: 139.3562 deg
    Height Above Ground: 50 ft
  4. Click OK.

    5. Raising the Place () object 50 feet above the ground simulates the height of the radar antenna.

  5. Bring the 3D Graphics window to the front.
  6. Right-click on Radar_Site () in the Object Browser.
  7. Select Zoom To.
  8. Use your mouse to obtain situational awareness of the radar site's location.

Radar Site

Insert the Antenna Servo System

Insert a Sensor () object to simulate a servo system for antenna positioning. In STK, you could create a spinning sensor to simulate a spinning radar antenna normally seen at an airfield. However, you will lock the sensor onto the aircraft and constrain the sensor to point in a limited area. This simulates the actual field of view of the airfield surveillance radar both horizontally and vertically.

  1. Select Sensor () in the Insert STK Objects tool.
  2. Select the Insert Default method.
  3. Click Insert....
  4. Select Radar_Site () in the Select Object window.
  5. Click OK.
  6. Rename the Sensor () Servo_System.

Define the Sensor Field of View

Define Servo_System's () 3 degree field of view using a Simple Conic sensor pattern. You will use the sensor's field of view for situational awareness when Servo_System() points the antenna at a target.

  1. Open Servo_System's () properties ().
  2. Select the Basic - Definition page.
  3. Set the Simple Conic - Cone Half Angle: value to 3 deg.
  4. Click Apply.

Target the Aircraft

Use the Targeted pointing type to point Servo_System () to Target_Acft().

  1. Select the Basic - Pointing page.
  2. Set the Pointing Type: to Targeted.
  3. Select Target_Acft () in the Available Targets list.
  4. Move () Target_Acft () to the Assigned Targets list.
  5. Click Apply.

Set Range and Elevation Angle Constraints

There are many types of radar systems. A typical airport surveillance radar's nominal range is 60 miles and the elevation angle of the beam can track from 0 to 30 degrees. Anything higher than 30 degrees is the cone of silence in which the radar cannot track the aircraft. Extend the Servo_System's () maximum range further than 60 miles in order to lock onto the aircraft when it's above the horizon.

  1. Select the Constraints - Basic page.
  2. Select Min: and Max: in the Elevation Angle section.
  3. Set the Min: value to 0 deg.
  4. Set the Max: value to 30 deg.
  5. Select Max: in the Range section.
  6. Set the value to 150 km.
  7. Click OK.

Determine Access

Determine when Servo_System () accesses Target_Acft (). This will give you a good idea of when the radar may be able to track the aircraft.

  1. Right-click on Servo_System () in the Object Browser.
  2. Select Access ().
  3. When the Access Tool opens, select Target_Acft () in the Associated Objects list.
  4. Click Compute.
  5. Click Access... in the Reports section.
  6. Click Report Units () in the Access report's toolbar.
  7. Select Time Dimension in the Units: Access window.
  8. Select Minutes (min) in the New Unit Value list.
  9. Click OK to close the Units: Access window.

    10. There are two accesses with a total duration of approximately 31 minutes.

  10. Close the report.

Generate an Azimuth Elevation Range Report

You have three constraints: a maximum elevation angle of 30 degrees, a minimum elevation angle of 0 degrees, and a maximum range of 150 km. Generate an azimuth-elevation-range (AER) report to see what affect these constraints have on your access report.

  1. Return to the Access Tool.
  2. Click AER... in the Reports section.
  3. Look at the Elevation (deg) column.
  4. Notice that the first access ends and the second access begins at an approximate elevation angle of 30 degrees.

    5. There is a break in access when the elevation angle exceeds 30 degrees due to the modeled cone of silence.

  5. When finished, close the AER report.
  6. Close the Access Tool.

Look at the Sensor's Field of View

Animate through the scenario to get a visual idea of when Servo_System () tracks Target_Acft ().

  1. Bring the 3D Graphics window to the front.
  2. Click Reset () in the Animation Toolbar.
  3. Right-click on Radar_Site ().
  4. Select Zoom To.
  5. Use your mouse to zoom out until you can see the entire aircraft flight route, the radar site, and the sensor's field of view.

    6. Sensor Field of View

  6. Click Decrease Time Step () in the Animation Toolbar until Time Step: is 3.00 sec.
  7. Click Start () in the Animation Toolbar to animate the scenario.
  8. Watch the animation. You can see the sensor turn off when the elevation angle exceeds 30 degrees, and turn back on when it returns to 30 degrees.
  9. When finished, click Reset () in the Animation Toolbar.

Insert an Airport Surveillance Radar

Insert a Radar () object to create an airport surveillance radar. We will model actual airport surveillance radar specifications that are easily available to the public.

  1. Select Radar () in the Insert STK Objects Tool.
  2. Select the Insert Default method.
  3. Select Servo_System () in the Select Object window.
  4. Click OK.
  5. Rename the Radar () ASR.

Model a Monostatic Radar

Model a Monostatic radar with a Search/Track mode. This will model a common antenna for both transmitting and receiving, and detect and track point targets.

To understand constants and equations used in STK, look at Search/Track Radar Constants and Equations in STK Help.

  1. Open ASR's () properties ().
  2. Select the Basic - Definition page.
  3. Note that Type: defaults to Monostatic.
  4. Note that Mode - Type: defaults to Search Track.

Define the Waveform

The waveform in our system will use a fixed pulse repetition frequency (PRF), with a PRF of ~1000 Hz. Radar systems often use multiple pulse integration to increase the signal-to-noise ratio. The PRF is the number of pulses of a repeating signal in a specific time unit. After producing a brief transmission pulse, the transmitter is turned off in order for the receiver to hear the reflections of that signal off of targets.

  1. Return to ASR's () properties (), Basic - Definition page.
  2. Note the Waveform is set to Fixed PRF.
  3. Note the default value of 0.001 MHz. We will keep that value since our system's PRF is ~1000 Hz.

Define the Pulse Width

Pulse width is the width of the transmitted pulse (the uncompressed RF bandwidth can also be taken as the inverse of the Pulse Width). Set the pulse width to one microsecond.

  1. Return to ASR's () properties (), Basic - Definition page.
  2. Click the units () drop down next to Pulse Width.
  3. Select usec.
  4. Set the Pulse Width value to 1 usec.
  5. Click Apply.

Define the Antenna Pattern

Model the antenna using the cosine squared aperture rectangular antenna pattern. The antenna transmit frequency for this radar is between 2.7-2.9 GHz.

  1. Select the Antenna tab on ASR's () properties (), Basic - Definition page.
  2. Click the ellipsis button (Component Selector) () beside the Type field.
  3. Select Cosine Squared Aperture Rectangular.
  4. Click OK.
  5. Select Use Beamwidth.
  6. Set the following:
    7. Option Value
    X Dim Beamwidth: 5 deg
    Y Dim Beamwidth: 1.4 deg
    Design Frequency: 2.8 GHz
    Main-lobe Gain: (if required, turn off Computed) 34 dB
    Efficiency: 55 %
  7. Click Apply.

Define the Radar Transmitter

The transmitter has a frequency range of 2.7-2.9 GHz, a peak power of 20 kW, and uses either linear or circular polarization. We will model linear polarization.

  1. Select the Transmitter tab on ASR's () properties (), Basic - Definition page.
  2. Select Frequency.
  3. Set the value to 2.8 GHz.
  4. Set the Power: value to 20 kW.
  5. Select the Polarization sub-tab.
  6. Select Use.
  7. Keep the default setting of Linear.
  8. Click Apply.

Set the Radar Receiver's Polarization

You don't have specific values regarding the low noise amplifier settings. These would be applied on the Receiver's Specs sub-tab. However, you know the polarization and want to add the receiver's system noise temperature. Let's set the polarization model type to Linear now.

  1. Select the Receiver tab on ASR's () properties (), Basic - Definition page.
  2. Select the Polarization sub-tab.
  3. Select Use.
  4. Keep the default setting of Linear.
  5. Click Apply.

Add the Radar Receiver's System Noise Temperature

Next, let's add the receiver's system noise temperature to your analysis. You will compute system noise temperature using the default values, and take into account Sun and Cosmic Background noise.

  1. Select the System Noise Temperature sub-tab.
  2. Select Compute.
  3. Select Compute in the Antenna Noise section.
  4. Select Sun.
  5. Select Cosmic Background.
  6. Click OK.
  7. Save () your scenario.

Probability of Detection

You will base the probability of detection (Pdet) on a value of 0.800000 or higher, one (1) being the highest value. You will also look at signal-to-noise ratio (SNR) and pulse integration. You will start by determining the Pdet of the large turboprop aircraft. Then, you will change Target_Acft's () constant RCS value to simulate a medium sized aircraft, then a small aircraft, and then a bird. Finally, you'll load a notional Aspect Dependent RCS file to see the difference between that and the constant value RCS sphere.

Compute Access

Compute Access () between ASR () and Target_Acft ().

  1. Right-click on ASR () in the Object Browser.
  2. Select Access... ().
  3. Select Target_Acft () in the Access Tool's associated objects list.
  4. Click Compute.

Generate a Radar SearchTrack Report

Now that you calculated Access between ASR () and Target_Acft (), generate a Radar SearchTrack report.

  1. Return to the Access Tool.
  2. Click Report & Graph Manager... under the Reports section.
  3. Expand () the Installed Styles list if necessary when the Report & Graph Manager opens.
  4. Select Radar SearchTrack report ().
  5. Click Generate....
  6. Click Show Step Value.Show Step Value At the top of the report.
  7. Change the Step: value to 30 sec.
  8. Press Enter on the keyboard or click Refresh () at the top of the report.

Understanding the Data

The content of a report or graph is generated from the selected data providers for the report or graph style. The data provider you'll focus on in this analysis is Radar SearchTrack.

Observe Pdet

Look at the difference between S/T Pdet1 and S/T Integrated Pdet in the report. S/T Pdet1 is based off of a single pulse. S/T Integrated PDet uses multiple pulses.

  1. Look at the first line in the report.
  2. Locate the two columns S/T Pdet1 and S/T Integrated Pdet.
  3. Note the difference in the values.

    4. Pulse integration improves the ability of the radar to detect targets by combining the returns from multiple pulses. You can see this in the S/T Pulses Integrated column in the report.

  4. Notice that overall tracking is good when using pulse integration (Pdet of 0.8 or higher).
  5. Keep the report open.

Observe SNR

Look at the difference between S/T SNR1 (dB) and S/T Integrated SNR (dB) in the report. S/T SNR1 (dB) is based on a single pulse and S/T Integrated SNR (dB) on pulse integration.

  1. Locate the two columns S/T SNR1 (dB) and S/T Integrated SNR (dB).
  2. Note the differences in the values.
  3. Again, the pulse integration allows for a better SNR.

Observe S/T Ambig Tgt Range

Look at the report to determine if distance from the radar has an effect on the data.

  1. Click Report Units () in the Radar SearchTrack report's toolbar.
  2. Select Distance Dimension in the Units: Radar SearchTrack window.
  3. Select Statute Miles (mi) in the New Unit Value list.
  4. Click OK to close the Units: Radar SearchTrack window.
  5. Scroll over to the right in the Radar SearchTrack report.
  6. Locate the S/T Ambig Tgt Range (mi) column. This column tells you how far the aircraft is from the radar site.
  7. You see improvement in values discussed above when the aircraft is closer to the radar site.
  8. Keep the report open.

Medium Sized Aircraft

Next, simulate a medium sized aircraft.

  1. Open Target_Acft's () properties ().
  2. Select the RF - Radar Cross Section page.
  3. Change the Constant RCS Value: to 10 dBsm.
  4. Click Apply.
  5. Return to the Radar SearchTrack report.
  6. Click Refresh () at the top of the report.
  7. Note the S/T Pdet1, S/T Integrated Pdet, S/T SNR1 (dB), and S/T Integrated SNR (dB) changes.

    8. The radar's ability to track this aircraft has diminished due to the aircraft's smaller RCS.

Small Sized Aircraft

Simulate a small sized aircraft.

  1. Return to Target_Acft's () properties ()..
  2. Change the Constant RCS Value: to 0 dBsm.
  3. Click Apply.
  4. Return to the Radar SearchTrack report.
  5. Click Refresh () at the top of the report.
  6. Note the S/T Pdet1, S/T Integrated Pdet, S/T SNR1 (dB), and S/T Integrated SNR (dB) changes.

    7. The radar's ability to track this aircraft has again diminished due to the aircraft's smaller RCS.

Birds and Stealth

Simulate a bird and a large, somewhat stealthy aircraft.

  1. Return to Target_Acft's () properties ().
  2. Change the Constant RCS Value: to -20 dBsm.
  3. Click Apply.
  4. Return to the Radar SearchTrack report.
  5. Click Refresh () at the top of the report.
  6. Note the S/T Pdet1, S/T Integrated Pdet, S/T SNR1 (dB), and S/T Integrated SNR (dB) changes.
  7. Looking at the results, you can only track birds within 10 miles of the airfield.

Aspect Dependent RCS Files

If you have an aspect dependent RCS file built for a specific target aircraft, your data will be much more realistic.

Load External File

Load an installed Aspect Dependent RCS file.

  1. Return to Target_Acft's () properties ().
  2. Change Compute Type: to External File.
  3. Click the ellipsis button () beside the Filename field.
  4. Browse to <STK install folder>\Data\Resources\stktraining\samples\SeaRangeResources\X-47B
  5. Select X-47B_Notional_Sample.rcs.
  6. Click Open.
  7. Click Reload.
  8. Click OK.

Visualize RCS Pattern

View the RCS pattern in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Target_Acft's () in the Object Browser.
  3. Select Zoom To.
  4. Use your mouse to get a good view of the aspect dependent RCS pattern.

    5. Aspect Dependent RCS Pattern

View Data

Refresh the Radar SearchTrack report to see the changes in SNR, PDet and Pulse Integration.

  1. Return to the Radar SearchTrack report.
  2. Click Refresh () at the top of the report.
  3. Note the S/T Pdet1, S/T Integrated Pdet, S/T SNR1 (dB), and S/T Integrated SNR (dB) changes.

    4. Depending on the reflection from the aircraft back to the radar, you could see fluctuation in your values. This is noticeable in the S/T Pulses Integrated column.

View RCS Data

Use the RCS graph style to visualize changes to RCS Decibel (dBsm). Note the cone of silence in the middle of the graph.

  1. Return to the Report & Graph Manager.
  2. Ensure the Object Type: is set to Access.
  3. Select Place-Radar_Site-Sensor-Servo_System-Radar-ASR-To-Aircraft-Target_Acft in the Object Type: list.
  4. Select Radar RCS graph () in the Installed Styles folder.
  5. Click Generate....
  6. Click Show Step Value.Show Step Value At the top of the graph.
  7. Change the Step: value to 1 sec.
  8. Press Enter on the keyboard or click Refresh () at the top of the report.

    9. Radar RCS Graph

  9. Save () your scenario.

Summary

You created a scenario that used the surface of the WGS84 as the central body obstruction. You created a simple flight route of an aircraft and changed its RCS value to simulate a large, four engined turboprop using a constant analytical RCS value. You created an airfield radar site and inserted a Sensor to create a servo system that was used to steer a radar antenna pattern inside its field of view in order to analyze various targets. You built a Radar using specifications typically found on air surveillance radars. You analyzed Pdet values for large, medium, small, and very small targets focusing on Pdet, SNR, and Pulse Integration. Finally, you used a notional aspect dependent RCS file that demonstrated both analytical and visual differences when compared to a constant RCS sphere.

On your own

Throughout the tutorial, hyperlinks were provided that pointed to in depth information of various tools and functions. Now is a good time to go back through this tutorial and view that information. Here are a few things you can do:

  • Move the radar site to an area that is using a local analytical terrain file and constrain your objects to use terrain for analysis.
  • Go on the Internet to find RCS values for other target types and analyze their Pdet values.
  • Change settings in the Radar's properties and see their effects on your analysis.