GPS Reception and Interference

STK Premium (Air) 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.

Required Capability Install: This lesson requires an additional capability installation for STK Terrain Integrated Rough Earth Model (TIREM). The TIREM install is included in the STK Pro software download, but requires a separate install process. Read the Readme.htm found in the STK install folder for installation instructions. You can obtain the necessary install by visiting http://support.agi.com/downloads or calling AGI support.

This lesson requires an internet connection and STK 12.9 or newer to complete in its entirety. If you have an earlier version of STK, you can complete a legacy version of this lesson.

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
  • Aviator
  • Terrain Integrated Rough Earth Model (TIREM)

Problem statement

Engineers and technicians require tools to simulate and analyze results before spending time and money performing on-site analysis. You are simulating a future training mission where a light aircraft will fly a search pattern over mountainous terrain. You need to determine how well the aircraft receives GPS transmissions. Although illegal to purchase and use in the United States, GPS jammers pose a threat to your communications. You want to know how these jammers will affect your communications. Using the jammer's specifications on the manufacturer's website, they state that the transmitter has a jamming radius of up to 400 meters. A team of engineers will drive to an area centrally located under the aircraft search pattern and determine if one of these devices will affect the aircraft's reception of the GPS signal. During this analysis, terrain must be taken into account. Prior to the mission, you will simulate the test in STK.

Solution

You can use STK's capabilities to understand how the jammer will affect your scenario.

  • Use STK Pro and a local, analytical terrain file to design the mountainous training area where the test will take place
  • Use STK's Communications capability to build GPS transmitters, receivers and measure interference against the GPS signal
  • Use STK's Aviator capability to create a search pattern for a light aircraft built to specifications
  • Use STK's Terrain Integrated Rough Earth Model (TIREM) capability to predict radio frequency propagation loss over irregular terrain
  • Combine these models to analyze GPS reception and interference.

Based on this analysis, engineers will confidently plan future missions, such as search and rescue, when there is a possibility of GPS interference in the rescue area of operations.

What you will learn

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

  • Design GPS Satellite Transmitters which use a Block IIR, L1 antenna pattern and transmits a signal from GPS satellites to an aircraft receiver
  • Design a GPS Receiver which uses a GPS Fixed Reception Pattern (FRPA) antenna pattern
  • Use radio frequency environmental models and system noise temperature calculations
  • Use Aviator to design a simple search pattern for a small aircraft
  • Determine GPS reception in the target area
  • Create a small GPS interference source
  • Use TIREM to predict radio frequency propagation loss over irregular terrain
  • Analyze GPS jamming

Video guidance

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

Creating a new scenario

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

  1. Launch STK ().
  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 GPS_Analysis
    Location Default
    Start 5 Jan 2023 19:00:00.000 UTCG
    Stop + 4 hrs
  4. Click OK when you finish
  5. Click Save () when the scenario loads. STK creates a folder with the same name as your scenario for you.
  6. Verify the scenario name and location in the Save As window.
  7. Click Save.

Save () often during this lesson!

Disabling Terrain Server

You're using a local terrain file for analysis. Turn off Terrain Server.

  1. Right-click on GPS_Analysis () in the Object Browser.
  2. Select Properties ().
  3. Select the Basic - Terrain page in the Properties Browser.
  4. Clear Use terrain server for analysis in the Terrain Server frame.
  5. Click Apply to accept your changes and keep the Properties Browser open.

Modeling the scenario's RF Environment

Since you're modeling the down link portion of a satellite transmission, you'll enable rain and atmospheric absorption models at the scenario level. A number of environmental factors can affect the performance of a communications link. A scenario's RF Environment properties page enables you to apply various models to your analyses. When enabled, the models will affect all RF phenomena in the scenario.

  1. Select the RF - Environment page.
  2. Select the Rain, Cloud & Fog tab.
  3. Select Use in the Rain Model frame.
  4. Use the default ITU-R model.
  5. Select the Atmospheric Absorption tab.
  6. Select Use.
  7. Use the default ITU-R model.
  8. Click OK to accept your changes and close the Properties Browser.

Adding Analytical and Visual Terrain

An STK (PDTT) file can be used analytically and visually (3D Graphics window) in your scenario. Add the terrain file to the scenario.

  1. Bring the 3D Graphics window to the front.
  2. Click Globe Manager () on the 3D Graphics window toolbar.
  3. Click Add Terrain/Imagery () in Globe Manager - Hierarchy toolbar.
  4. Select Add Terrain/Imagery... ().
  5. Click the Path: ellipsis () in the Globe Manager: Open Terrain and Imagery Data dialog box.
  6. Browse to Windows (C:) - Program Files - AGI - STK 12 - Data - Resources - stktraining - imagery.
  7. Click OK.
  8. Select the StHelens_Training.pdtt check box.
  9. Click Add .
  10. Click Yes when prompted to use terrain for analysis. By selecting Yes, you are loading the (PDTT) file analytically and visually into the scenario.

Visualizing the Terrain

View the terrain in the 3D Graphics window.

  1. Right-click on StHelens_Training.pdtt () in Globe Manager.
  2. Select Zoom To ().
  3. Use your mouse to move around and zoom in and out to view the terrain in the 3D Graphics Window.

Inserting Constellation objects

Use the Insert STK Objects tool to load the GPS Constellation using orbital elements from GPS almanac files. The Almanac files can be stored in local directories or pulled from AGI Servers (internet connection required). STK creates a constellation that includes all of the satellites in the almanac. Keep in mind, you can build Constellation objects yourself by loading a Constellation object using the Insert Default or Define Properties method and assigning objects required for your analysis.

  1. Select Satellite () in the Insert STK Objects tool.
  2. Select the Load GPS Constellation () method.
  3. Click Insert... .

    4. Once loaded, you will see each individual Satellite () object and a Constellation ( ) object containing all of the satellites.

  4. Open GPSConstellation's () properties ().
  5. Select the Basic - Definition page.
  6. Observe that each GPS satellite has been moved to the Assigned Objects list.
  7. Click OK to close the Properties Browser.

Inserting a Transmitter object

Attach a Transmitter () object to the first GPS satellite in your scenario.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Select the first Satellite () object in the Select Object dialog box.
  3. Click OK.
  4. Right-click on Transmitter1 () in the Object Browser.
  5. Select Rename.
  6. Rename Transmitter1 () to GPS_Tx1.

Modeling GPS Satellite Transmitter

You will use a GPS Satellite Transmitter Model. This model lets you set up multiple antenna beams, each with its own specs and its own polarization and orientation properties. For this lesson, you are configuring one beam.

  1. Open the GPS_Tx1's () properties ().
  2. Select the Basic - Definition page in the Properties Browser.
  3. Click the Transmitter Model Component Selector ().
  4. Select GPS Satellite Transmitter Model in the Transmitter Models list in the Select Component dialog box.
  5. Click OK to accept your selection and to close the Select Component dialog box.

 Modifying beam specs

Use Beam Specs to modify beam parameters of your beam.

  1. Select the Beams tab.
  2. Select the Beam Specs sub-tab.
  3. Enter 27.45 W in the Power: field.
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling GPS global antenna pattern

Use Antenna to modify antenna parameters for your beam. For this analysis, you will use the GPS global antenna pattern. This antenna models a GPS satellite antenna operating a Global Beam on the L1 or L2 frequency channel for Block type II-A satellites. You will keep things simple and model the Block IIR, L1 antenna type.

  1. Select the Antenna sub-tab.
  2. Select the Model Specs sub-sub-tab.
  3. Ensure GPS Global is selected in the Antenna Model field.
  4. Select IIR, L1 for Block Type.

    5. If you look in the Block Type list, you can see antenna types for the other block types.

  5. Enter 80 % in the Efficiency: field.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Setting right-hand circular polarization

Polarization is a property of an electromagnetic wave that describes the orientation of the electric field vector with reference to the antenna's orientation. Antennas used in GPS systems are right-hand circularly polarized.

  1. Select the Polarization sub-sub-tab.
  2. Select Use.
  3. Open the pull-down menu.
  4. Select Right-hand Circular.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Setting data rate

The transmitter's data rate is a compound dimension with data bits and time as simple dimensions. For public use, the GPS design uses Coarse/Acquisition code transmitted at a data rate of 1023 kb/sec.

  1. Select the Model Specs tab.
  2. Enter 1.023 Mb/Sec in the Data Rate: field.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling the modulator

STK Communications allows you to select from multiple modulators including user-defined modulators. The GPS Coarse / Acquisition code uses the binary Phase-shift keying (BPSK) modulation technique, which is the default setting. You will use the Power Spectral Density (PSD). The Power Spectral Density option allows the scenario to model the actual spectral shape of the transmitted signal based on the modulation, data rate, etc. 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.

  1. Select the Modulator tab.
  2. Select Use Signal PSD.
  3. Enter 1 in the Set Number of Spectrum Nulls: field.
  4. Notice that setting one spectrum null sets Bandwidth: to 2.046 MHz.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Visualizing the antenna pattern

The 3D Graphics Attributes page for the transmitter allows you to control the 3D display of contour lines and antenna patterns. Volume graphics displays the shape and gain levels of antenna beams.

  1. Select the 3D Graphics – Attributes page.
  2. Select Show Volume in the Volume Graphics frame.
  3. Click Apply to accept your changes and to keep the Properties Browser open.
  4. Bring the 3D Graphics window to the front.
  5. Right-click on the Satellite () object to which you attached the Transmitter () object in the Object Browser.
  6. Select Zoom To.

    7. GPS Transmitter Antenna Pattern

    Blue shows the maximum gain and red shows the minimum gain.

  7. Return to GPS_Tx's () properties () when finished.
  8. Clear the Show Volume check box.
  9. Click OK to accept your changes and to close the Properties Browser.

Reusing the GPS transmitter

Copy and paste GPS_Tx1 () to the remaining GPS satellites in your scenario.

  1. Select GPS_Tx1 () in the Object Browser.
  2. Click Copy () on the Object Browser toolbar.
  3. Select the next Satellite () in the Object Browser.
  4. Click Paste () on the Object Browser toolbar.
  5. Using this method, Paste () the transmitter to the remaining GPS satellites.

    6. You only have to copy the transmitter the first time, then paste it onto the remaining satellites. To save time, you can use the Ctrl+C and Ctrl+V methods to copy and paste your transmitters to the satellites.

    Although there is no need to rename the new transmitters in this tutorial (you can just keep the STK numbering), this is one instance where in a real world scenario, matching transmitter names to the satellite can help you when running a report or graph.

Creating an Area Target

The Area Target () object models a region on the surface of the central body. You will use an Area Target () object to outline the training area. Furthermore, the Area Target () object simplifies creating a flight route for the test aircraft.

  1. Insert an Area Target () object using the Area Target Wizard () method.
  2. Type Test_Area in the Name: field once the Area Target Wizard opens.
  3. Click Insert Point four times.
  4. Set the following in the Points frame in the order shown:
    5. Latitude Longitude
    46.00 deg -123.00 deg
    46.00 deg -122.00 deg
    47.00 deg -122.00 deg
    47.00 deg -123.00 deg
  5. Click OK to accept your changes and to close the Area Target Wizard.

Making the Area Target visible

Earlier in the scenario you turned off Terrain Server. This affects the view of the Area Target object when using a local terrain file. You need to change your Scenario object's properties so you can view the Area Target on the terrain.

  1. Open GPS_Analysis's () properties ().
  2. Select the 3D Graphics - Global Attributes page.
  3. Open the On Terrain: pull-down menu in the Surface Lines frame.
  4. Select On.
  5. Click OK to accept your changes and to close the Properties Browser.

Decluttering Labels

Objects located on the surface of the terrain could be covered by the terrain which makes them unreadable. You can fix this by making a change to the 3D Graphic window's properties.

  1. Bring the 3D Graphics window to the front.
  2. Click Properties () on the 3D Graphics window's toolbar.
  3. Select the Details page.
  4. Select Enable in the Label Declutter frame.
  5. Click OK to accept your change and to close the Properties Browser.

Viewing the Area Target

View Test_Area () in the 3D Graphics window.

  1. Right-click on Test_Area () in the Object Browser.
  2. Select Zoom To.
  3. Zoom out on the 3D Graphics window to view the entire outline of Test_Area ().

    4. Area Target

  4. Look at the lower right hand corner of the test area. This is Mount St. Helens.
  5. Use your mouse to zoom back to the surface and explore the terrain.

Inserting an Aircraft Object

Insert an Aircraft () object to simulate the aircraft that will fly a search pattern inside of the designated test area.

  1. Insert an Aircraft () object using the Insert Default () method.
  2. Rename Aircraft1 () to Test_Acft.

Aviator

Use the Aviator propagator to create the flight route. You will choose the type of aircraft you want to model and Aviator takes into account the performance characteristics of that aircraft as it creates the route. This provides a more accurate and realistic model for your aircraft.

  1. Open Test_Acft's () properties ().
  2. Select the Basic - Route page.
  3. Open the Propagator: pull-down menu.
  4. Select Aviator.
  5. Click Apply to accept your change and to keep the Properties Browser open.
  6. Click Optimize STK for Aviator when the Flight Path Warning dialog box opens.
  7. Read the information in the window.
  8. Click OK to close the Flight Path Warning dialog box.

Selecting the aircraft model

Choose the aircraft model you want in your scenario. You will model a light aircraft using the pre-defined Basic General Aviator model.

  1. Click Select Aircraft () in the Initial Aircraft Setup toolbar.
  2. Select Basic General Aviation in the User Aircraft Models list in the Select Aircraft dialog box.
  3. Click OK to close the Select Aircraft dialog box.
  4. Click Apply to accept your change and to keep the Properties Browser open.

Modeling the first phase of flight

Inserting the first procedure

Every mission must have at least one phase.

  1. Right-click on Phase 1 () in the Mission List.
  2. Select Insert First Procedure for Phase... ().

Selecting site type

You can use an STK Area Target to define a waypoint at the centroid of the selected area target, or, combined with the Area Target Search procedure, to define a search area.

  1. Select STK Area Target () in the Select Site Type: list in the Site Properties dialog box.
  2. Select Test_Area () in the Link To: list.
  3. Click Next >.

Selecting procedure type

An Area Target Search procedure conducts a search pattern flight - comprised of raster parallel lines - within the selected area target site.

  1. Select AreaTargetSearch () in the Select Procedure Type: list once the Procedure Properties dialog box opens.
  2. Set the following in the Search Options frame:
    3. Option Value
    Max Separation 5 nm
    Course Mode Override
    Centroid True Course 90 deg
  3. Enter 5.00 in the Turn Factor: field, located in the Enroute Options frame.

    4. The Turn Factor is the maximum amount - expressed as a multiplier - that the turn radius will be increased to minimize the bank angle required to complete the turn.

  4. Click Finish to close the Procedure Properties dialog box.
  5. Click OK to accept your changes and to close the Properties Browser.

Viewing the aircraft flight route

View Test_Acft's () flight route in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Test_Area () in the Object Browser.
  3. Select Zoom To.
  4. Zoom in or out using your mouse so that you can see Test_Acft's () flight route.

    5. Aircraft Flight Route

Aviator calculated a search pattern based on the parameters that you set. The course is defined based on Test_Area's () centroid.

Inserting GPS Receiver

Insert and attach a Receiver () object to Test_Acft ().

  1. Insert a Receiver () object using the Insert Default () method.
  2. Select Test_Acft () in the Select Object dialog box.
  3. Click OK.
  4. Rename Receiver1 () to GPS_Rx.

Using a complex receiver model

The complex receiver model enables you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open the GPS_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Click the Receiver Model Component Selector ().
  4. Select Complex Receiver Model in the Receiver Models list in the Select Component dialog box .
  5. Click OK to close the Select Component dialog box.

Setting model specs

Adjust the low noise amplifier (LNA) losses and gain. A low noise amplifier is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio.

  1. Select the Model Specs tab.
  2. Set the following:
    3. Option Value
    Antenna to LNA Line Loss 1 dB
    LNA Gain 20 dB
    LNA to Receiver Line Loss 10 dB
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling GPS fixed reception pattern antenna

The receiver requires a GPS fixed reception pattern antenna (GPS FRPA). A GPS FRPA is a single element, omni-directional antenna designed to receive GPS satellite signals from about five to ten degrees above the horizon and up.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select GPS FRPA () once the Select Component dialog box opens.
  5. Click OK to close the Select Component dialog box.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling linear polarization

The receiver is linearly polarized with the electrical field aligned with the reference axis. Although it would be optimal for the receiver's antenna polarization to match the transmitter's, it is common to transmit with circular polarization but receive using linear polarization. You will lose power due to the polarization mismatch which will be modeled.

  1. Select the Polarization sub-tab.
  2. Select Use.
  3. Ensure the Polarization is set to Linear. Linear is the default selection.
  4. Set the Cross-Pol Leakage Threshold to -30 dB.

    5. You only use Cross-Pol Leakage with a Receiver () object. Whenever STK detects a complete polarization mismatch between the transmitted signal and the received signal under ideal conditions, the cross polarization leakage value is applied to model the less than ideal real world performance.

  5. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the antenna's orientation

STK provides methods to specify the orientation of the antenna coordinate frame relative to the coordinate frame of the parent object. The antenna’s default elevation is 90 degrees, which points the antenna boresite along its parent object's positive Z vector. The positive Z vector of an Aircraft () object points to nadir. You need to point the antenna up along the negative Z vector.

  1. Select the Orientation sub-tab.
  2. Enter -90 deg in the Elevation: field.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling System Noise Temperature

The Receiver's System Noise Temperature allows you to specify the system's inherent noise characteristics. These can help simulate real-world RF situations more accurately.

  1. Select the System Noise Temperature tab.
  2. Select the Compute option.
  3. Enter 4.8 dB in the LNA - Noise Figure: field, located in the LNA frame.
  4. Select the Compute option in the Antenna Noise frame.
  5. Select the following check boxes:
    • Earth
    • Sun
    • Atmosphere
    • Rain
    • Cosmic Background
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling a Terrain Mask

Use the Terrain Mask constraint when access to the object is constrained by any terrain data in the line of sight to which access is being calculated. Test_Acft () is flying in a mountainous area and you are using analytical terrain.

  1. Select the Constraints - Active page.
  2. Click Add new constraints () in the Active Constraints toolbar.
  3. Select Terrain Mask in the Constraint Name list in the Select Constraints to Add dialog box.
  4. Click Add.
  5. Click Close to close the Select Constraints to Add dialog box.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Visualizing the antenna pattern

Set the volume graphics and view the antenna pattern in the 3D Graphics Window.

  1. Select the 3D Graphics - Attributes page.
  2. Select the Show Volume check box in the Volume Graphics frame.
  3. Click Apply to accept your changes and to keep the Properties Browser open.
  4. Bring the 3D Graphics window to the front.
  5. Right-click on the Test_Acft () in the Object Browser.
  6. Select Zoom To.

    7. Receiver Antenna Pattern

  7. Return to GPS_Rx's () properties () when finished.
  8. Clear Show Volume.
  9. Click OK to accept your changes and to close the Properties Browser.

Determining GPS reception

Determine the signal quality between the GPS transmitters and the GPS receiver. A link budget reports the values that determine the GPS reception. For the purposes of this scenario, you will focus on one column in the link budget: C/No (dB * Hz). The carrier to noise density ratio (C/No) where C is the carrier power and No = kT (Boltzmann's constant x system temperature) is the noise density. It is equivalent to C/N with a normalized Bandwidth (B=1). In this instance, the compound dimension being used is Spectral Density and the Base Dimension is Bandwidth*Ratio. The Bandwidth is Hertz (Hz).

A value of greater than or equal to 35 means you have good GPS reception.

  1. Right-click on GPS_Rx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select all of the Satellite () objects in the Associated Objects list in the Access Tool.
  4. Right-click on one of the Satellite () objects.
  5. Select Expand All.
  6. Select GPS_Tx1 ().
  7. Hold down the Ctrl key on your keyboard.
  8. Select the remaining Transmitter () objects.
  9. Click .

    10. Be patient. This could take a couple of minutes.

Creating a link budget report

Generate a Link Budget report using the Report & Graph Manager.

  1. Click Report & Graph Manager... in the Access Tool.
  2. Select all of the Access () objects in the Object Type: list once the Report & Graph Manager opens.
  3. Select the Specify Time Properties option in the Time Properties frame.
  4. Set the following:
    5. Option Value
    Use step size / time bound Selected
    Step size: 60 sec
  5. Select the Link Budget - Detailed () report in the Installed Styles folder, located in the Styles frame.
  6. Click Generate... .

    7. Any fields in the report where it says "Data Unavailable" means there was no access between the GPS receiver and GPS transmitter on that satellite.

  7. Browse to the C/No (dB * Hz) column.
  8. Scroll down through the report.

    9. How is the reception between your GPS receiver and the satellite transmitters based on C/No (dB*Hz) of greater than or equal to 35? Keep in mind you're going to see fluctuations due to RF environment, location of satellites (overhead, low on the horizon), distance, etc.

  9. View other data based on settings:
    • Atmos Loss (dB)
    • Rain Loss (dB)
    • Tatmos (K)
    • Train (K)
    • Tsun (K)
    • Tearth (K)
    • Tcosmic (K)
    • Tantenna (K)
  10. Close the link budget - detailed report, the Report & Graph Manager, and the Access tool.

Inserting Test Team as a place object

Insert a Place () object that will simulate the location of the test team.

  1. Insert a Place () object using the Insert Default () method.
  2. Rename Place1 () to Test_Team.

Setting Test Team's Location

The test team is deploying a small, portable GPS jammer near the center of the test area.

  1. Open the Test_Team's () properties ().
  2. Select the Basic - Position page.
  3. Set the following in the Position frame:
    4. Option Value
    Latitude 46.499 deg
    Longitude -122.494 deg
    Height Above Ground 2 m

    Height Above Ground raises Test_Team () 2 meters above the surface of the terrain. When you attach a Transmitter () object to Test_Team (), the Transmitter () object's antenna will also be 2 meters above the terrain's surface.

  4. Click OK to accept your changes and to close the Properties Browser.

Viewing Test Team

View the Test Team's () location in the 3D Graphics window. This is where the GPS jammer will be deployed. Look at its location compared to the Test_Acft's () route.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to Test_Team ().
  3. Use your mouse to view the area where the GPS jammer will be deployed and its location compared to the test aircraft's flight route.

    4. Test Team and Aircraft

Determining the range from the Test Team to the aircraft

The manufacturer claims the jammer's maximum effectiveness is 400 meters. Determine how far the aircraft is from the test team during the test.

  1. Right-click Test_Team () in the Object Browser.
  2. Select Access... ().
  3. Select Test_Acft () in the Associated Objects list in the Access Tool.
  4. Click AER in the Reports frame. AER computes an azimuth / elevation / range report.
  5. Scroll down to the Statistics in the AER report.
  6. Note the minimum and maximum range of the Test_Acft () from Test_Team ().

    7. The aircraft never gets closer than approximately 2.6 kilometers from the test team. This is well outside the manufacturer's claimed radius of 400 meters.

  7. Close () the AER report when finished.
  8. Click Close to close the Access Tool.

Inserting a portable jammer

Insert and attach a Transmitter () object to Test_Team ().

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Select Test_Team () in the Select Object dialog box.
  3. Click OK.
  4. Rename Transmitter2 () to Jammer.

Configuring the GPS jammer

Most small, portable GPS jammers have similar specifications. You will model the jammer using a Complex Transmitter Model.

  1. Open Jammer’s () properties ().
  2. Select the Basic - Definition page.
  3. Click the Transmitter Model Component Selector ().
  4. Select Complex Transmitter Model () in the Transmitter Models List in the Select Component dialog box.
  5. Click OK to accept your selection and to close the Select Component dialog box.

Setting model specs

Model the frequency and power.

  1. Select the Model Specs tab.
  2. Set the following options:
    3. Option Value
    Frequency 1.57542 GHz
    Power 35 W (Watts)
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling a Dipole Antenna pattern

For this analysis, you will use a dipole antenna pattern. Dipole antennas are modeled analytically using modeling equations that can be found in standard antenna texts.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Model Component Selector ().
  4. Select Dipole () in the Antenna Models list in the Select Component dialog box.
  5. Click OK to accept your choice and to close the Select Component dialog box.
  6. Set the following options:
    7. Option Value
    Design Frequency 1.57542 GHz
    Length 7 in
    Efficiency 80%
  7. Click Apply to accept your changes and to keep the Properties Browser open.

Modeling Vertical Polarization

Set the Antenna's Polarization to vertical.

  1. Select the Polarization sub-tab.
  2. Select Use.
  3. Select Vertical in the pull-down menu.
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Setting Modulator model

The Narrowband Uniform analytical modulator models narrowband jammers.

  1. Select the Modulator tab.
  2. Select Narrowband Uniform for the Name.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Preparing the Transmitter object for the Terrain Integrated Rough Earth Model (TIREM)

Disable Line-of-sight, Terrain Mask, or Az-El Mask constraints to take advantage of the over-the-horizon analysis functionality of TIREM.

  1. Select the Constraints - Active page.
  2. Clear Enable - Line Of Sight in the Active Constraints section.
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Adding Terrain Integrated Rough Earth Model

TIREM adds fidelity to the calculation and dynamic modeling of point-to-point line-of-sight effects for link performance in communications. It does this by taking into account the effect of irregular terrain and non-line-of-sight effects. The maximum height for these models is 30 km.

Recall that you enabled rain and atmospheric absorption models, at the scenario level, to predict you link budget between the satellites' transmitters and the aircraft's receiver. The jamming device needs to take into account how terrain will affect its performance. You can set this RF Environment setting at the object level.

  1. Select the RF - Environment page.
  2. Select the Atmospheric Absorption Tab.
  3. Select Use.
  4. Click the Atmospheric Absorption Model Component Selector ().
  5. Select the newest TIREM model (the higher the number, the newer the model) once the Select Component dialog box opens.
  6. Click OK to accept your selection and to close the Select Component dialog box.
  7. Click OK to accept your changes and to close the Properties Browser.

Adding receiver interference sources

You can add interference sources to an RF receiver's properties. Then, you can assess their impact on the performance of the receiver.

  1. Open GPS_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Select the Interference tab.
  4. Select Use.
  5. Select Test_Team/Jammer () in the Available Emitters list.
  6. Move () Test_Team/Jammer () to the Assigned Emitters list.
  7. Click OK to accept your changes and to close the Properties Browser.

    8. Be patient. This can take a couple of minutes.

Checking for Interference

You can view all the transmitters on one report. Generate an STK pre-built link budget report.

  1. Right-click on GPS_Rx () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select Access as the Object Type in the Report & Graph Manager.
  4. Select all of the Access () objects in the Object Type: list except () Place-Test_Team-To-Aircraft-Test_Acft.
  5. Select the Specify Time Properties option in the Time Properties frame.
  6. Set the following:
    7. Option Value
    Use step size / time bound Selected
    Step size 60 sec
  7. Select the Link Budget - Interference () report in the Installed Styles folder, located in the Styles frame.
  8. Click Generate... .
  9. Scroll to the right and locate the C/No (dB*Hz) and C/(No+Io) (dB*Hz) columns in your generated report. The C/(No+Io) (dB*Hz) column measures interference.
  10. Scroll down through the report to see how the hand held jamming device is affecting the aircraft's GPS reception.

    11. Column One: No Interference / Column Two: Interference

    Scrolling through the report, you can see that the jammer is definitely affecting GPS reception.

Saving your work

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

Summary

This tutorial demonstrated a link budget that focused on a specific value: C/No (dB * Hz). Representational averages were used for both rain and atmospheric absorption losses. GPS Transmitters and the aircraft's GPS receiver were built to model authentic civilian hardware. When the C/No (dB * Hz) value was equal to or greater than 35, GPS reception was good. Actual website specifications for illegal hand held GPS jammers lead consumers to think they have a very limited jam radius. The jammer specifications used in this scenario stated that the jammer had a jamming radius of up to 400 meters. As you can see, the jammer reached out much further than that when targeting C/No (dB * Hz). You can verify this by matching Access range times against successful interference periods (C/No (dB*Hz) versus C/(No+Io) (dB*Hz)). You also took into account the effect terrain had on the jammer using TIREM. This tutorial is an excellent example of applying real-world hardware specifications and environmental factors into an STK scenario to obtain a better understanding of what the engineering team should expect to see during an actual test.

On your own

Additional analysis:

  • Match the Antenna Type to the different GPS block types, and rerun the link budget analysis.
  • Match the receiver's polarization to the transmitter's polarization, and rerun the link budget analysis.
  • Place two or three jammers in different locations through the test area, and analyze interference.
  • Place a jammer on the plane and a GPS receiver on the ground, and analyze interference.