Introduction to Radio Frequency Interference Analysis

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 STK 12.5 or newer to complete.

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.

Problem statement

Engineers and operators require a quick way to determine radio frequency (RF) interference. A customer plans to launch a new communications satellite. The customer is concerned that a new constellation of low Earth orbiting (LEO) satellites will create RF interference against a ground site receiver because they have similar frequencies. The customer needs to determine if interference will take place and how often.

Solution

Use STK and STK's Communications capability to add the new communications satellite and the constellation of LEO satellites in orbit with their transmitters and receivers. Determine if RF interference could occur between the LEO transmitters and the ground site's receiver that communicates with the new communications satellite.

What you will learn

Upon completion of this tutorial, you will have a basic understanding of the following:

  • Determining RF interference
  • The Walker tool

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: RF_Interference_Analysis
    Location: Default
    Start: 15 May 2022 16:00:00.000 UTCG
    Stop: + 24 hr
  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 will not use Terrain in this analysis, so you can turn off the Terrain Server.

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

Inserting the communications satellite

You will use the Orbit Wizard to place the communications satellite into its expected orbit.

  1. Select Satellite () in the Insert STK Objects tool.
  2. Select the Orbit Wizard () method.
  3. Click Insert....

Orbit Wizard

The Orbit Wizard is a satellite-level tool designed to assist you in creating any one of several standard orbits or designing your own satellite orbit. The configurable options available will depend on the orbit type selected.

  1. When the Orbit Wizard opens, open the Type: shortcut menu.
  2. Select Orbit Designer.
  3. Type Comm_Sat in the Satellite Name: field.
  4. Enter the following in the Orbital Elements frame:
    5. Option Value
    Semimajor Axis: 42164 km
    Eccentricity: 0.0027
    Inclination: 9 deg
    Argument of Perigee: 302.5 deg
    RAAN: 61 deg
    True Anomaly: 33 deg
  5. Click OK to accept your changes and to close the Orbit Wizard.

Inserting the ground site

The ground site is located at a U.S. Air Force Base.

  1. Insert a Facility () object using the From Standard Object Database () method.
  2. Type Offutt in the Name: field when the Search Standard Object Data dialog box opens.
  3. Click Search.
  4. Select Offutt AFB SATCOM Terminal in the Results: list using the Local Database Data Source.
  5. Click Insert.
  6. Click Close after Offutt_AFB_SATCOM_Terminal () appears in the Object Browser.

Changing Offutt AFB SATCOM Terminal's altitude

Place Offutt AFB SATCOM Terminal on the surface of the WGS84. WGS84 or World Geodetic System 1984 is an Earth-fixed reference frame.

  1. Open Offutt_AFB_SATCOM_Terminal's () properties ().
  2. Select the Basic - Position page.
  3. Select the Use terrain data check box in the Position frame.
  4. Click OK to accept your changes and close the Properties Browser.

Inserting the communications satellite's transmitter

Attach a transmitter to the communications satellite.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Select Comm_Sat () in the Select Object dialog box.
  3. Click OK to accept your selection and close the Select Object dialog box.
  4. Right-click on Transmitter1 () in the Object Browser.
  5. Select Rename.
  6. Rename Transmitter1 () to CommSat_Tx.

Using a Medium Transmitter model

Only some of the communications satellite transmitter's specifications are defined, so you will use a Medium Transmitter model for your analysis. The Medium Transmitter provides more flexibility by letting you specify gain and power separately, instead of entering their product (EIRP) directly as in the Simple model. The default antenna model for a Medium Transmitter is isotropic which is defined as a hypothetical antenna having the same radiation in all directions.

  1. Open CommSat_Tx's () properties ().
  2. Select the Basic - Definition page.
  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 accept your selection and to close the Select Component dialog box.

Updating the Model Specs

  1. Select the Model Specs tab.
  2. Set the following:
    3. Option Value
    Frequency: 1.5 GHz
    Gain: 10 dB
  3. Click OK to accept your changes and to close the Properties Browser.

Inserting Offutt AFB SATCOM Terminal's servo motor

The receiver antenna is steerable. In STK, you use a targeted sensor that functions as a servo motor.

  1. Insert a Sensor () object using the Insert Default () method.
  2. Select Offutt_AFB_SATCOM_Terminal () in the Select Object dialog box.
  3. Click OK to accept your selection and close the Select Object dialog box.
  4. Rename Sensor1 () to Servo_Motor.

Simple Conic sensor

You will use a Simple Conic sensor type.

  1. Open Servo_Motor's () properties ().
  2. Select the Basic - Definition page.
  3. Change the Cone Half Angle: value to 2 deg in the Simple Conic frame. You want to do this for situational awareness, but it is not required analytically.
  4. Click Apply.

Raising the servo motor's altitude

The antenna is located 10 feet above the ground. The parent object's positive Z body points to the center of the Earth. In order to raise the sensor above the ground, you need to use a negative value.

  1. Select the Basic - Location page.
  2. Open the Location Type: shortcut menu.
  3. Select Fixed.
  4. Change Z: to -10ft in the Fixed Location frame.
  5. Click Apply.

Targeting the communications satellite

The Pointing page enables you to set parameters to determine how a sensor is aimed (for example, with respect to its parent object, the central body, objects selected for tracking, and others).

  1. Select the Basic - Pointing page.
  2. Open the Pointing Type: shortcut menu.
  3. Select Targeted.
  4. Open the Track Mode: shortcut menu.
  5. Select Receive.
  6. Select Comm_Sat () in the Available Targets list.
  7. Move () Comm_Sat () to the Assigned Targets list.
  8. Click OK to accept your changes and to close the Properties Browser.

Attaching a receiver to the ground site's servo motor

The servo motor will point the receiver's antenna.

  1. Insert a Receiver () object using the Insert Default () method.
  2. Select Servo_Motor () in the Select Object dialog box.
  3. Click OK to accept your selection and close the Select Object dialog box.
  4. Rename Receiver1 () to Satcom_Rx.

Using a Complex Receiver model

The Complex Receiver model allows you to select among a variety of analytical and realistic antenna models and to define the characteristics of the selected antenna type.

  1. Open Satcom_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Click the Receiver Model Component Selector ().
  4. When the Select Component dialog box opens, select Complex Receiver Model () in the Receiver Models list.
  5. Click OK to accept your selection and to close the Select Component dialog box.

Using a Gaussian Antenna Model

The Gaussian Antenna Model uses an analytical model of a Gaussian beam. The model is like a parabolic antenna within about -6 dB relative to the boresight. The Gaussian Antenna Model is the default antenna model.

  1. Select the Antenna tab.
  2. Set the following:
    3. Option Value
    Design Frequency: 1.5 GHz
    Diameter: 3 m
  3. Click OK to accept your changes and to close the Properties Browser.

What is a Simple Link Budget?

You can create a Simple Link Budget by creating a Link Budget in the Access tool. The Link Budget Report is a specialized Access Report for basic link budget analysis and is available using the Link Budget button in the Reports frame of the Access tool. In this analysis, you will use the Simple Link Budget to calculate bit error rate (BER), which reflects of how often errors occur in the transmission of digital data. Obviously, you want a low BER value because that means you have less errors over time.

Creating a Simple Link Budget

For the purposes of your analysis, a bit error rate (BER) less than 1.000000e-10 is acceptable.

  1. Right-click on Satcom_Rx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Expand () Comm_Sat () in the Associated Objects list when the Access Tool opens.
  4. Select CommSat_Tx ().
  5. Click Compute.
  6. Click Link Budget... in the Reports frame.
  7. Scroll to the right to locate the BER column when the report opens. Your bit error rate values look good. They are well below 1.000000e-10.
  8. Close the link budget report and the Access tool.

Creating a Seed Satellite

You will create the proposed constellation of LEO satellites using the Walker Tool. The original satellite that creates the Walker constellation is referred to as the seed satellite. The satellites generated using the Walker tool are referred to as children. You will use the Orbit Wizard to create the seed satellite from which the other satellites will be derived.

  1. Insert a Satellite object () using the Orbit Wizard () method.
  2. When the Orbit Wizard opens, set the following:
    3. Option Value
    Type: Circular
    Satellite Name: LEO_Sat
    Inclination: 45 deg
    Altitude: 2000 km
    RAAN: 0 deg
  3. Click OK to accept your changes and to close the Orbit Wizard.

Reusing a transmitter

The transmitter on the seed satellite has the same properties as the transmitter on the communications satellite. You can reuse the existing transmitter. This is a quick way to create a new object having identical properties to an object already existing in the scenario.

  1. Select CommSat_Tx () in the Object Browser.
  2. Click Copy () in the Object Browser toolbar.
  3. Select LEO_Sat ().
  4. Click Paste () in the Object Browser toolbar.
  5. Rename CommSat_Tx1 () to LEO_Tx.

Walker Constellations

The Walker Tool makes it easy to generate a Walker constellation using the Two Body, J2, J4, or SGP4 orbit propagators. Open the Walker tool by highlighting the satellite in the Object Browser and selecting Walker... from the Satellite shortcut menu.

  1. Right-click on LEO_Sat () in the Object Browser.
  2. Select Satellite in the shortcut menu.
  3. Select Walker... in the second shortcut menu.
  4. Set the following in the Walker Tool:
    5. Option Value
    Type: Delta
    Number of Sats per Plane 10
    Number of Planes: 10
    Inter Plane Phase Increment: 1
  5. Click Create / Modify Walker.
  6. Click Close when finished propagating the Walker constellation.
  7. Save () the scenario. Your seed Satellite object has been saved in the scenario folder for later use if you need it.
  8. Select LEO_Sat () in the Object Browser.
  9. Click Delete () in the Object Browser toolbar.
  10. Click Delete in the Delete Object dialog box.

Interference sources

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

  1. Open SATCOM_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Select the Interference tab.
  4. Select the Use check box.
  5. Select Transmitter () in the Selection Filter frame.
  6. Move () all of the transmitters from the Available Emitters list to the Assigned Emitters list.
  7. Select Comm_Sat/CommSat_Tx in the Assigned Emitters list.
  8. Remove () Comm_Sat/CommSat_Tx from the Assigned Emitters list.
  9. Click OK to accept your changes and to close the Properties Browser.

Creating a custom report

You can easily create a custom report that focuses on bit error rates and potential interference.

  1. Right-click on SATCOM_Rx () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select CommSat_Tx () in the Associated Objects list when the Access tool opens.
  4. Click Report & Graph Manager... under the Reports frame.
  5. Select the My Styles () folder in the Styles frame when the Report & Graph Manager opens.
  6. Click Create new report style () in the Styles toolbar.
  7. Type BER Interference to rename the new report style.
  8. Press the Enter key on your keyboard to open BER Interference's properties ().

Link Information data provider and elements

When the report properties open, you need to choose the correct data provider and required elements for your analysis. The Link Information data provider provides the link budget for a single access between a transmitter and a receiver.

  1. Select the Content page.
  2. Expand () Link Information () in the Data Providers list.
  3. Move () the following Data Provider Elements to the Report Contents list in the sequence shown:
  • Time
  • BER
  • BER+I (Bit error rate in the presence of interference)

Setting options for data providers

You want to set options for the data providers. Both the BER and BER+I notations default to a Floating Point, but you want to use Scientific notation.

Updating BER notation

  1. Select Link Information-BER in the Report Contents list.
  2. Click Options... .
  3. When the Options: Section 1, Line 1, Link Information-BER dialog box opens, open the Notation: shortcut menu in the Data Format frame.
  4. Select Scientific (e).
  5. Click OK to accept your change and to close the Options: Section 1, Line 1, Link Information-BER dialog box.

Updating BER+I notation

  1. Select Link Information-BER+I in the Report Contents list.
  2. Click Options... .
  3. When the Options: Section 1, Line 1, Link Information-BER+I dialog box opens, open the Notation: shortcut menu in the Data Format frame.
  4. Select Scientific (e).
  5. Click OK to accept your change and to close the Options: Section 1, Line 1, Link Information-BER+I dialog box.
  6. Click OK to accept your changes and to close the Properties Browser.

Generating the custom report

Any BER+I value greater than 1.000000e-10 indicates interference to your communications system.

  1. Select BER Interference in the My Styles () folder located in the Styles frame.
  2. Click Generate... .
  3. Compare the BER and BER+I columns.

Determining whether there is RF interference

You should see some changes between the BER and BER+I values. As you scroll down through the report, you will see times during which your BER+I values are well over the established threshold for effective communications (1.000000e-10). This means the constellation of LEO satellites will cause interference between your ground site and the communications satellite.

Summary

With the advent of thousands of small satellites being placed in orbit for many forms of communication, STK is an outstanding tool that you can use to simulate how those satellites might interfere with existing or planned communications systems. In your scenario, you created a link budget between your ground site and a communications satellite. The resulting data showed good communications. You used the Walker Tool to create a proposed constellation of satellites that could interfere with your communications. Using the Access tool and the Report & Graph Manager, you determined that the constellation of satellites will interfere with portions of your communications.

Saving your work

  1. Close any reports, tools and properties.
  2. Save () your work.

On your own

You could use the instructions in this tutorial to determine intentional communications jamming or other forms of communications interference.