Contours | Vectors | Antenna Beam Patterns

Communications Graphics Walkthrough

Note: To do this exercise you will need a valid license of STK Professional Edition and STK/Communications.

This walkthrough introduces you to some of the 2D and 3D graphics capabilities available in STK/Communications. In this exercise you will:

• Define and display contours of antenna gain and other RF characteristics in the 2D Graphics window.
• Use vectors to enhance the 3D display of a transmitter on a GEO satellite.
• Create and vary 3D representations of antenna beam patterns.

This tutorial is intended for advanced users and assumes you have gone through the ProTutorial.

Set the Context

Start STK. Create a scenario with a Start time and Epoch of 1 Jun 2003 12:00 UTCG and a Stop time 24 hours later. Use the Orbit Wizard to create a Geosynchronous satellite with all parameters left at their default values.

Define and Display Contours

Receiver Antenna Gain Contour

1. Attach a Receiver to the satellite.
2. Open the Definition page of its Basic properties.
3. Select Complex Receiver Model as the Type.
4. Click the Antenna… tab.
5. Confirm that the Main-Lobe gain is approximately 41 dB.
6. Click Apply to save the settings you made (selection of the Complex Receiver model.)

Comm Contours

1. Open the receiver's 2D Graphics - Contours properties page.
2. Turn On the Show Graphics option.
3. Set the Add Method to Explicit.
4. Enter 41 (the approximate maximum gain for this antenna in dB) in the Level field.
5. Click Add Level to add it to the Level list.
6. Use the Level field and the Add button to add the following additional gain levels to the list: 40, 30, 20, 10, 0, -10, and -20.
7. Set the Color Method to Explicit.
8. Select the first entry in the Level list.
9. Assign it a Color using the color picker.
10. In a similar fashion, assign colors to each of the other gain levels.
11. Uncheck the Relative to Maximum option.
12. Click Apply.

Show in 2D Graphics

1. Reset the 2D Graphics window (shown here zoomed) to see the gain contours display:

2. 

3. To label the contour lines with the appropriate gain levels, return to the Contours page.
4. Turn On the Show option in the Level Labels field.
5. Click Apply.

Saving Time and Effort

There are three options that you could have chosen to simplify and speed up the generation of gain contours:

• You could have used the Relative to Maximum option instead of having to retrieve the maximum gain value from the Antenna Parameters.
• You could have used Start, Stop, Step as the Add Method instead of entering each gain level manually.
• You could have used Color Ramp as the Color Method instead of assigning a color individually to each gain level.

We will now run through the above process again, using these convenient options. Before you start, select each entry in the Level list, and click Remove to delete it.

Tip: To multi-select and remove all the entries at once, select the first entry, hold down the Shift key, and select the last entry. Then, with all entries highlighted, click Remove. You can also use Remove All.

Check the Relative to Maximum box. Select Start, Stop, Step as the Add Method and enter a Start value of 0, a Stop value of -60, and a Step of -10. Click Add Level to populate the Levels list.

Note: Here, a value of 0 relative to maximum is equivalent to the maximum gain value, i.e. approximately 41 dB. A value of -10 is 10 dB less than the maximum, i.e. approximately 31 dB, and so on. The method used here starts at the maximum gain value and steps it down by increments of 10 dB until the Stop value (approximately -19 dB) is reached.

Set the Color Method to Color Ramp, and select a Start and End Color to define the segment of the spectrum from which colors are to be automatically assigned to the contour lines. Click Apply. Reset the 2D Graphics window to see the new contours.

Some Other Things to Try On Your Own

Before leaving receiver antenna gain contours, try some other options that are provided on the Contours page:

• Change the Add Method to Explicit, and add a new level of -35 dB to the Level list.
• Select one or more entries from the Level list, and change the Line Style (e.g. to dotted or dashed).
• Change the Line Width for all gain levels to a different thickness.
• Select the Show at Altitude option, and enter an Altitude value of 5000 km. Instead of representing gain levels where the antenna beam intersects the Earth’s surface (the normal case), the contour pattern now represents gain levels where the beam crosses the selected altitude. When you reset the 2D Graphics window, the contour pattern will noticeably contract.

After each change, click Apply on the Contours page, and reset the 2D Graphics window.

Note: Line Width settings always apply to all contour levels in the pattern; Line Style settings apply only to levels that you select.

For a receiver, contour graphics are available only for Antenna Gain. Additional options are provided for a transmitter, as discussed in the next section.

Transmitter Contours

In the following exercises, in addition to trying out another contour type, you will become acquainted with special graphics options applicable to multibeam antennas.

Set Up the Multibeam Transmitter

1. Open the 2D Graphics - Contours properties page for the receiver.
2. Turn Off the Show Graphics option.
3. Click OK.
4. Add a Transmitter to the satellite.
5. Open the transmitter's Basic - Definition page.
6. Select Multibeam Transmitter Model as the Model Type.
7. Click Add twice to add two more beams.

8. Note: Maximum Gain (the default) is specified as the Beam Selection Strategy in the Beams tab in the Basic Definition properties. This has consequences for, among other things, contour graphics, as you will see later in this exercise.

9. Multi-select all three beams.
10. Click Orient….
11. Set the Elevation Initial Value to 87 deg.
12. Set the Azimuth Increment Value to 120 deg.
13. Click OK.
14. Click Apply on the Definition page.

Define Contours

1. Open the 2D Graphics - Contours properties page for the transmitter.
2. Ensure the Show Graphics is On.
3. Select EIRP (Effective Isotropic Radiated Power) as the Type.
4. Turn On the Relative to Maximum box.
5. Select Start, Stop, Step as the Add Method.
6. Enter a Start value of 0, a Stop value of -60, and a Step value of -10.
7. Click Add Level.
8. Use Color Ramp as the Color Method.
9. Click Apply.
10. Reset the 2D Graphics window.

Recall that the Beam Selection Strategy (specified in the Beams tab in the Basic Definition properties) is Maximum Gain.

1. Open the transmitter's Basic - Definition properties page.
2. Select Aggregate Active Beams as the Beam Selection Strategy.
3. Click Apply on the Definition page.
4. Reset the 2D Graphics window. The contour graphics now reflect the aggregate EIRP levels of all three beams:

Improve Resolution

You can improve the resolution of the contours.

1. Open the transmitter's 2D Graphics - Contours properties page.
2. Turn On the Set azimuth and elevation resolution together option.
3. Set the Azimuth Resolution to 0.5 deg.
4. Click Apply on the Contours page.
5. Reset the 2D Graphics window. There should be a noticeable change in the resolution of the contour graphics.

Note: The Points field, immediately below the Resolution field, will automatically update to reflect the finer resolution value.

Contours in 3D

Contours can also be displayed in the 3D Graphics window.

1. Open the 3D Graphics - Attributes properties page for the transmitter.
2. Turn on the Show Lines option for Contour Graphics.
3. Click Apply.
4. Reset the 3D Graphics Window.

1. Open the Basic - Definition properties page for the transmitter.
2. Select the Antenna tab.
3. Select the Orientation tab.
4. Set a Relative Position Offset of 1000000 m for the X axis.
5. Click Apply on the Definition page.
6. Reset the 2D Graphics window.

After viewing the effect of the offset on the contour graphics, go back and set the offset back to zero.

In addition to EIRP, transmitter contour graphics are available for Antenna Gain, Flux Density, and RIP (Received Isotropic Power). Before leaving transmitter contours, you may want to try out one or more of these contour types using the Relative to Maximum option and the Start, Stop, Step method to avoid having to determine or guess absolute values.

Note: Unlike Antenna Gain, which can be retrieved directly from the Antenna properties, determination of appropriate values for the other contour types requires creating additional objects, calculating access, and generating link budget reports.

Before moving on to vectors, open the 3D Graphics - Attributes properties pages for the receiver and the transmitter, and make sure that the Show Lines option for Contour Graphics is unchecked on both.

Enhance the 3D Display with Vectors

In the following exercise you will:

• configure the satellite and the transmitter to display body axes,
• mount the transmitter on a sensor and set the sensor spinning, and
• observe the display of the satellite and transmitter axes in the 3D Graphics window.

1. Open the 3D Graphics - Vector properties page for the satellite.
2. Turn On the Show option for Body Axes.
3. Ensure that the Axes field is set to Earth Inertial.
4. Turn on Scale Relative to Model under Component Size.
5. Ensure that the Scale is set to 1.2.
6. Click OK.
7. Reset the 3D Graphics window.
8. Click View From/To ().
9. Select the satellite as the View From and View To object.
10. Click OK.
11. Zoom and rotate the 3D view, as necessary, to see the axes.

Add a Sensor

1. With the satellite still selected in the Object Browser, add a sensor.
2. Open the sensor’s Basic - Pointing properties page.
3. Set the Pointing Type to Spinning.
4. Set the Spin Rate to 0.2 revolutions per minute.
5. Open the sensor’s 3D Graphics - Attributes properties page.
6. Increase the Projection %Translucency value to 100.
7. Click OK.

Note: The translucency is increased so that display of the sensor cone in the 3D Graphics window does not interfere with display of the vector graphics.

Moving Objects

1. Highlight the transmitter in the Object Browser.
2. Right-click and select Cut from the Edit menu.
3. Highlight the sensor in the Object Browser.
4. Right-click and select Paste from the Edit menu.

Tip: Cut-and-paste is an easy way to move objects around in the scenario hierarchy. You can also use copy-and-paste to create duplicates of objects that you have previously created and configured. When you move or copy an object that has sub-objects, the sub-objects are moved or copied along with their parent object.

Add A Vector

1. Open the 3D Graphics - Vector properties page for the transmitter.
2. Turn On the Show option for Body Axes.
3. For the Axes field, click the ellipsis (…) button.
4. Ensure that the transmitter’s body frame is selected as the reference axes.
5. Click OK to close the Select Reference Axes dialog.
6. Ensure that the Component Size Scale is set to 1.2.
7. Click Apply.
8. Briefly animate the scenario to observe the transmitter axes as they rotate with respect to the satellite axes in the 3D Graphics window.

9. 

10. Return to the 3D Graphics - Vector properties page for the transmitter.
11. Turn on the Show option for Sun Vector.
12. Ensure the Scale is set to 1.2.
13. Click Apply.
14. Reset the 3D Graphics window.

A representative selection of vectors and axes is listed on the transmitter’s 3D Graphics - Vector properties page, but you are by no means limited to those. Click Add… to browse through the large variety of vectors, axes, and other components that you can add to your 3D display.

Before moving on to antenna beam patterns, you may want to experiment a bit with other graphics settings on the transmitter’s Vector page, or click Add… and introduce other components into your 3D display.

When you are finished, return to the 3D Graphics - Vector properties page for the transmitter, uncheck the Show option for the body axes and the sun vector (as well as any other components you may have added), and click OK. Then open the satellite’s 3D Graphics - Vector properties page, uncheck the Show option for the body axes, and click OK.

Display and Vary Antenna Beam Patterns

Use cut-and-paste to move the transmitter off the sensor and place it back on the satellite. Delete the sensor.

1. Open the 3D Graphics - Attributes properties page for the transmitter.
2. Turn on the Show Volume option under Volume Graphics.
3. Increase the Gain Scale to 800 km.
4. Turn On the Set azimuth and elevation resolution together option.
5. Set the resolution to 0.5 deg.
6. Click Apply on the Attributes page.
7. Reset the 3D Graphics window.
8. Change the View From/To to be from the satellite to the Earth, if it is not already.

Tip: If you are still seeing contour graphics, you can remove them by unchecking the Show Lines option on the 3D Graphics - Attributes page for the receiver and/or the transmitter, as necessary. If you only see two beams, you need to remove the offset you introduced earlier: open the transmitter's Basic - Definition page, click Multibeam Antenna..., select the first beam, click Modify..., and change the Relative Position Offset for X to 0 m.

The colors of the beam pattern represent gain levels, running the spectrum from red (relatively high gain) to violet (relatively low gain). The size of the beam pattern is determined by the setting for Gain Scale (see above), which specifies the number of kilometers per dB of gain.

To add contour graphics back into the 3D view, return to the transmitter's 3D Graphics - Attributes properties page, check Show Lines under Contour Graphics, click Apply, and reset the 3D Graphics window.

You can also bring the transmitter’s body axes back into the picture. For better display, increase the Scale to 5.5.

Now turn off all 3D display options for the transmitter: contours, antenna beam pattern (volume graphics), and axes. With the 3D Graphics Window active, select View From/To ,and set the view to be from the satellite to the satellite.

Change the Receiver

1. Open the receiver’s Basic - Definition properties page.
2. Click the Antenna tab, and then the Model Specs tab, if necessary.
3. Change the antenna's Model Specs Type to a Helix model.
4. Set the Efficiency of the antenna to 100%.
5. Set the Diameter to 0.1 m.
6. Expose the receiver's Model Specs page by clicking the upper Model Specs tab.
7. Turn off the Auto Track option.
8. Set the Frequency to 2.5 GHz.
9. Click Apply.
10. Open the 3D Graphics - Attributes properties page.
11. Turn on Show Volume.
12. Set the Azimuth Resolution to 1 deg.
13. Set the Elevation Resolution to 1 deg.
14. Click Apply.
15. Reset the 3D Graphics window to see the gain pattern of the helix antenna.
16. Return to the receiver's 3D Graphics - Attributes properties page.
17. Turn on the Show as wireframe option, and click Apply.
18. Zoom in close to see the wireframe effect.

This exercise illustrates only a few of the things you can do with antenna beam patterns. Experiment with other Definition settings (e.g. frequency, antenna model, antenna size) and graphics options. Observe the results in the 3D Graphics window.