CommAntennaTutorial

Working with the Antenna Object Overview The Communications module has a new antenna object. In previous versions, users had to create receiver and transmitter objects, and then set antenna parameters on each one. This becomes tedious when you have many transmitters and receivers, all functioning on the same physical antenna hardware. With a new antenna object, you can set the antenna properties once and then link to the antenna when it is used by a receiver and transmitter. In this tutorial, you will use the new Communications antenna object to analyze the link between a satellite transmitter and a ground-based receiver. You will also learn the difference between the embedded antenna object and the linked antenna object. Note: This tutorial requires valid STK Pro and STK Communications licenses. Embedded Antenna vs. Linked Antenna There are two ways to use antennas in STK: embedding or linking. The embedded antennas are defined within the properties of a parent receiver or transmitter. These antennas are specific to that parent object, which means that they cannot be used by multiple transmitters/receivers. The linked antennas are defined independently of any single receiver or transmitter, which enables the sharing of the antenna by several transmitters and receivers. If you have multiple transponders attached to communication GEO satellite, you can create a single antenna object, and have the transmitters and receivers link to the one antenna. This is convenient for two reasons: 1. The parameters of the antenna object only have to be defined once, rather than re- entered for each receiver and each transmitter. 2. When changing the properties of the antenna, this can be done once on the linked antenna object, rather than on every embedded antenna in every transmitter and every receiver. Create a Scenario 1. Create a scenario. 2. When the STK: New Scenario Wizard appears, name it “CommAntenna.” 3. Leave the default scenario time. 4. Click OK. Add a Facility and a Satellite 1. From the Insert Object tool, select the Facility object and Insert Default method. Click Insert… 2. Rename the facility “Station.” By default, new facilities are created at the latitudinal and longitudinal coordinates of AGI headquarters near Philadelphia. Now that you have a facility in your scenario, you need something for the facility to track. In this case, it will be a satellite. 3. From the Insert Object tool, select the Satellite object and Orbit Wizard method. Click Insert… 4. When the Orbit Wizard appears, set the Type to Molniya. 5. Name the satellite “Satellite.” 6. Leave all the other defaults. 7. Click OK. 8. Close the Insert STK Objects window. 9. Zoom in on the 2D Graphics window to get a better view of your facility and satellite. Add an Antenna and Receiver to the Facility The satellite will be sending transmissions to your facility. In order to accept them, you will need an antenna and receiver attached to the facility. Let’s model these now. 1. Add an Antenna to Station . 2. Rename the Antenna “StationAntenna.” 3. Open StationAntenna’s Properties Browser to the Basic – Definition page. 4. Use the … button to set the Type to Parabolic. 5. Leave all other defaults. 6. Click OK. 7. Attach a Receiver ( ) to Station . 8. Rename the receiver “StationRcv.” 9. Open the StationRcv’s Properties Browser to the Basic – Definition page. 10. Use the … button to set the Type to Complex Receiver Model. 11. On the Antenna tab, set the Reference Type to Link. Note that Antenna/StationAntenna is selected as the Antenna Name. 12. Click OK. This will link the receiver to the antenna you created. You will notice that you cannot change the properties of the linked antenna in the receiver’s properties. Any changes that need to be made to the antenna, such as orientation, will need to be made to the properties of the linked antenna object. Add an Antenna to the Satellite Your satellite will be tracking the facility so it can transmit data to the facility. To do this, you need to attach a sensor that will act as a pointing mechanism for the antenna. Let’s start by adding a sensor to the satellite. 1. Attach a sensor to the Satellite . 2. Rename the sensor “TrackingPlatform.” 3. Open the TrackingPlatform Sensor’s Properties to the Basic – Pointing page. 4. Set the Pointing Type to Targeted. 5. Select Station in the Available Targets list and move it to the Assigned Targets list. 6. Click OK. Now you have a sensor that will target the facility as the satellite moves over the horizon. By creating the antenna object as a “child” of the sensor object, the antenna will inherit the orientation of the sensor. 7. Attach an Antenna to the TrackingPlatform Sensor . 8. Rename the antenna “SatelliteAntenna.” 9. Open SatelliteAntenna’s Properties to the Basic – Definition page. 10. Use the … button to set the Type to Parabolic. 11. Leave all other defaults. 12. Click OK. Since the transmitter will be linked to the antenna, which already inherits the pointing defined by the sensor, no further pointing is needed. We will attach the transmitter to the satellite. To attach the transmitter to the sensor AND link it the antenna which is attached to the sensor would be to “double-count” the pointing effect of the sensor. As a safeguard from unintended results, STK will not permit this. 13. Attach a Transmitter ( ) to the Satellite. 14. Rename it “SatelliteXmtr.” 15. Open SatelliteXmtr’s ( ) Properties Browser to the Basic – Definition page. 16. Use the … button to set the Type to Complex Transmitter Model. 17. On the Antenna Tab, set the Reference Type to Link. Note that Sensor/TrackingPlatform/Antenna/SatelliteAntenna is the Antenna Name. 18. Click OK. Generate a Report You will be concentrating on an examination of the antenna Eb/No and the Bit Error Rate (BER). To check these values, create a Link Budget Report. 1. Right-click on StationRcv in the Object Browser and select Access… . 2. Select SatelliteXmtr in the Associated Objects panel. 3. Click the Report & Graph Manager… button. 4. Select the Link Budget – Detailed report from the Installed Styles folder. 5. Click Generate… The Link Budget – Detailed report shows several more communication parameters than just the simple link budget report. Based on the report, how is the BER? If it is not acceptable, what can you do to the receiver to improve it?