STK Comms

Designing Communication Systems

Version 9

Analytical Graphics, Inc.

www.agi.com [email protected] 610.981.8000 2011-06

OverviewWelcome to the Designing Communication Systems training course. This course is a collection of instructor-led exercises that provide hands-on experience with a variety of the features and functions on which STK is built. It will familiarize you with the STK Software Suite, specifically STK Communications

This course will focus on the core modules that are commonly used to perform various types of analysis. In order to complete the exercises herein you must have a fully functional copy of the following products:

STK Professional STK/TIM (Terrain, Imagery, and Maps) STK/Integration Module STK/Communications with TIREM STK/Radar STK/Coverage

Adding a Simple Receiver .............................................................................. 15Create A Satellite ........................................................................................... 16Calculate the Link Budget .............................................................................. 20Analyzing a Dynamic Platform ....................................................................... 22Create a Transmitter on the Aircraft .............................................................. 24S_AmGEO Needs a Receiver......................................................................... 25Save Your Work ............................................................................................. 27

Will Directed Antennas Help Improve Your Communication Performance? ............................................................................. 29Problem Statement........................................................................................ 30Model the World!........................................................................................... 30Create a Link Budget Report.......................................................................... 31Adding an Antenna to the Satellite ................................................................ 31Embedded vs. Linked Antennas .................................................................... 34Adding a Comple 35Calculate the Link 36x Receiver........................................................................... Budget ..............................................................................Table Of Contents

Can the Military Model Surveillance Communication in South America? ....................................................................................... 7Problem Statement.......................................................................................... 8Welcome To STK!............................................................................................ 8Model the World!............................................................................................. 9Save Your Scenario ........................................................................................ 11Insert STK Objects Tool ................................................................................. 11Model an Area of Interest .............................................................................. 12Model Washington D.C.................................................................................. 14

Table Of Contents

Verify Performance in 3D............................................................................... 36Other Ways to Introduce Objects .................................................................. 37Pointing the Receiver and Transmitter........................................................... 39Change Your Perspective............................................................................... 40Recalculate the Link Budget .......................................................................... 41Pointing the Transmitter to the Facility .......................................................... 41Change Your Perspective............................................................................... 42Calculate the Link Budget .............................................................................. 43Additional Gains and Losses .......................................................................... 43What is a Plugin ............................................................................................. 44AER Report .................................................................................................... 46Custom Graph................................................................................................ 46Save Your Work ............................................................................................. 47

Can You Determine the Effect of Polarization On Your Communication System? ...................................................................................... 49Problem Statement........................................................................................ 50Model the World!........................................................................................... 50Polarization..................................................................................................... 51Set the Polarization of the Transmitter .......................................................... 51Set the Polarization of the Receiver............................................................... 52Create the Link Budget Report ...................................................................... 52Change the Receiver Type............................................................................. 53Change Receiver to RHC ............................................................................... 54Load the Plugin for Aircraft Polarization ......................................................... 55Edit the Receiver Plugin................................................................................. 56Link Budget Comparison................................................................................ 56Model the Second Region ............................................................................. 56Multibeam Analysis........................................................................................ 59Create a Multibeam Receiver ........................................................................ 59Creating a New Link Budget Report .............................................................. 60Create A Second Beam ID Report ................................................................. 61Save Your Work ............................................................................................. 61

Can You Visualize Communications Contours and Beam Patterns in 2D and 3D?............................................................................................... 63Problem Statement........................................................................................ 64Model the World!........................................................................................... 64Viewing Contours........................................................................................... 65Move the Beam ............................................................................................. 664

Show Graphics in 3D ..................................................................................... 67Add a Base of Operations .............................................................................. 68

TABLE OF CONTENTS

Add a Receiver to Tulcan ............................................................................... 69Add a Targeted Sensor to Tulcan................................................................... 69Data Display Panel ......................................................................................... 71Custom 3D Views.......................................................................................... 72Add Vector ..................................................................................................... 74Create the Angle ............................................................................................ 74Save Your Work ............................................................................................. 76Viewer Exercise ............................................................................................. 76

Can the Environment Affect Your Communication System?...... 79Problem Statement........................................................................................ 80Model the World!........................................................................................... 81Theory ............................................................................................................ 81Create a Link Budget ..................................................................................... 81Add a Rain Model........................................................................................... 82Add Rain Outage to DC Receiver................................................................... 83Atmospheric Absorption Models ................................................................... 84Modeling Temperature .................................................................................. 86Other Environmental Models......................................................................... 86Rain Model Plugin .......................................................................................... 87Atmospheric Absorption Plugin ..................................................................... 88View Terrain in 3D Graphics Window ............................................................ 89Adding TIREM................................................................................................ 90Clear the Plugin.............................................................................................. 92Save Your Work ............................................................................................. 92

Which Military Base Is In the Best Location to Accept Communication Data? ........................................................................................... 93Problem Statement........................................................................................ 94Model the World!........................................................................................... 94Theory ............................................................................................................ 95What is Coverage?......................................................................................... 95Narrow Your Focus ........................................................................................ 96Define Coverage ............................................................................................ 97Insert Peterson and McChord........................................................................ 98Coverage Definition ....................................................................................... 99Set the Contour Colors ................................................................................ 100Figure of Merit ............................................................................................. 101Viewing Results in the 2D Window ............................................................. 102Find the Best Place ...................................................................................... 103Atmospheric Effects .................................................................................... 1035

Increase the Gain of the Transmitter ........................................................... 104

Table Of Contents

Save Your Work ........................................................................................... 1046

Can the Military Model Surveillance Communication in South America?

In this exercise, you will use STK and the STK/Communications module. You will look at two different levels of fidelity for transmitters and receivers. Upon completion of this exercise, you will be able to:

Understand Communications in the STK environment. Add a transmitter or receiver to an STK object. Calculate the Link Budget for a transmitter/receiver pair. Modify the modulation of a signal carrier.


Problem StatementThe United States military has decided to conduct an undercover surveillance operation in the northern region of South America to monitor transmissions taking place between renegade militant groups distributing weapons. The military has ordered its group of system engineers to evaluate and create an imaging communications system to capture data from the specified region and relay that information back to the military command and control center in Washington D.C.

A surveillance aircraft will be deployed to monitor the activity. This aircraft needs to relay the information to a GEO satellite, which will then send the information to the control center in Washington D.C.

Break it DownYou have some information that may be helpful. Heres what you know:

The total surveillance time is two (2) hours. The Washington D.C. facility has a Hawkeye 1.6 M receiver with a G/T value of

23.7 dB/K. You have a GEO satellite that has a simple transmitter with a frequency of 12

GHz and an EIRP of 23 dBW. The satellite has a receiver to accept transmissions from the aircraft. That receiver

is a medium receiver with a 37 dB gain. Your aircraft is equipped with a medium transmitter with a frequency of 15 GHz,

a power of 12 dBW, and a gain of 28 dB. The aircraft is modeled after a Link 22 aircraft.

The aircraft transmitter has a modulation of QPSK and a data rate of 128 kb/sec.

SolutionUse STK and STK/Communications module to model a scenario that can be used to conduct undercover surveillance of South America.

Welcome To STK!The first thing you need to do is launch STK, and create a new scenario.

1. Double-click the STK icon ( ) on the desktop.

Everything in STK begins with a scenario. A scenario is STK's name for an instance of an analytical or operational task that you are modeling using STK. In STK a scenario is represented by an icon of an idealized scene. The STK scenario creates the context, or environment, within which all other objects in your scenario exist. You can create an unlimited number of scenarios with STK, however only one scenario 8

can be open at a time.


When STK launches, the Welcome to STK! dialog will appear. Using the options available here, you can create new scenarios, open existing scenarios, or exit the STK application.

FIGURE 1. Welcome to STK!

2. Click the Create a New Scenario button.

The Welcome to STK! dialog also provides an option to disable this feature in the event that you prefer to create and manage your scenarios manually. If the Welcome to STK! dialog were disabled, you could create a new scenario by either:

Clicking the New ( ) button on the Default toolbar, or Selecting the New ( )option from the File menu.

FIGURE 2. Scenario icon

Model the World!When you click the Create a Scenario button, the New Scenario Wizard dialog appears. You can input basic information about your scenario here. Lets set the basic parameters for scenario creation now.

1. Enter the following in the New Scenario Wizard dialog:9


2. Click OK to create your scenario.

Get Off on the Right Foot--Stay OrganizedOnce you begin working with STK, you may create and save several scenarios with many objects in a short time. The most helpful technique to manage your scenario files is to save each scenario into its own folder, and give the folder and the scenario file (*.sc) the same name as in the example above. Youll find that this simple rule of thumb will help you to manage your scenarios more efficiently for the following reasons:

It decreases the likelihood that you will accidentally overwrite your previous work, especially if you have objects with the same names in different scenarios (e.g. several satellites named 'LEO').

It helps keep your work organized, so that it is easier to find a given scenario later. It makes it easier to share your scenarios with others.

When you use the New Scenario Wizard to create a new scenario, STK will automatically create a new directory in your default user directory (C:\Documents and Settings\Student\My Documents\STK 9) with the same name that you input for the scenario name and store all of your scenario files as described above.The scenario itself is saved as an object (*.sc) and each object within the scenario (e.g., satellites, facilities, planets, stars, receivers and transmitters, etc.) is saved individually.

TABLE 1. New Scenario Wizard options

Option Value

Name Network_Surveillance

Description Model surveillance communication in South America

Location C:\Documents and Settings\student\My Documents\STK 9

Analysis Period Start time: Default Start Time

End Time: + 2 hours10


FIGURE 3. Object Browser

When you create a new scenario, STK updates the Object Browser to include the new scenario and creates the appropriate visualization windows. Once in the Object Browser the objects can be named and properties can be applied.

Save Your Scenario

1. When the scenario loads, click Save ( ).2. Verify the scenario name and location and click Save.

Once a scenario is saved the first time, it will be saved to the same location every time you click the Save button. The Save button is always available, and always saves the entire scenario, regardless of the window or object that is selected.

Insert STK Objects ToolWhen a scenario is created, the Insert STK Objects tool appears automatically unless the Do not show me this again option is enabled. From here, you can begin the object creation and insertion process. The Insert STK Objects tool makes it easy to insert and configure some of the most commonly used individual objects. The left-hand pane lists commonly used STK objects. When you select an object on the left, all of the 11

methods available for introducing that class of object will be listed on the right. The


process and data that you will have to provide will depend on the object class and introduction method selected.

FIGURE 4. Insert STK Objects tool

The Insert STK Objects tool can be customized using the options available on the New Object page of the Application Preferences.

1. Click the Edit Preferences... button.2. Select the New Object page.3. Locate the Define Default Creation Methods area.

The Objects list contains all of the available objects in STK. When an object is selected, all of the available methods for creating and configuring that object display in the Method list to the right. You can include or exclude options from the Insert STK Objects tool by selecting them in the list and enabling or disabling the Show object in insert new object tool.

4. When you finish, click Cancel to dismiss the New Object preferences page.

Model an Area of InterestYou will be conducting surveillance on a particular region in South America. An area target is a good way to highlight that region visually. Lets create the area target now.

1. Bring the Insert STK Object tool ( ) to the front.2. Select the following:12


3. Click the Insert... button.4. Set the Name to Surveillance_Area.5. Click the Insert Point four (4) times. These will be the latitude and longitude

bounds of your area.6. Insert the following coordinates:

7. Click OK on the Area Target Wizard to insert your surveillance area.

Get a Better Look

1. Reset ( ) the animation.2. Right-click Surveillance_Area ( ) in the Object Browser.3. Select Zoom To.4. Mouse around in the window to get a better look at Surveillance_Area ( ).

FIGURE 5. 3D View: 3D view of Surveillance_Area

TABLE 2. Create Surveillance_Area

Option Value

Select an Object To Be Inserted: Area Target

Select a Method: Area Target Wizard

TABLE 3. Coordinates of Surveillance_Area

Latitude Longitude

-1 deg -77 deg

-1 deg -78 deg

1 deg -78 deg

1 deg -77 deg13


Model Washington D.C.Now you have a model of a meaningful world, but your world needs more objects. Your headquarters is located in Washington D.C. You can use the City Database to find Washington D.C.

STK provides two objects that can be used to model a point-of-interest on the surface of the central body--Facilities ( ) and Targets ( ). Facilities and targets are almost identical in properties and behavior, the only difference between them is their icon.

Insert the FacilityNow, you can create and position the facility object.

1. Bring the Insert STK Objects tool ( ) to the front.2. Select the following:

3. Click the Insert... button.

The City Database tool will be launched. The City Database tool contains thousands of cities around the world. Individual city information includes the exact location of the city, the type of city, and more.

4. Enable the City Name criteria.5. Enter Washington in the adjacent textbox.6. Click the Search button.7. Select the Washington District of Columbia entry from the list.8. Set the Color to Red.9. Click the Insert button.10. Close the City Database search tool.

The Properties BrowserEach STK object and visualization window has its own set of properties, which are organized into categories (e.g., Basic, 2D Graphics, Constraints, etc.). Customizing properties creates a meaningful environment for the other objects in your scenario. The properties used to define STK objects are organized in the Properties Browser. When you open the Properties Browser you will see the properties for whatever object or visualization window is selected in the STK Workspace.

TABLE 4. Insert Washington DC

Option Value

Select an Object To Be Inserted: Facility

Select a Method: Select From City Database14

1. Open Washingtons ( ) properties ( ).


2. Select the 2D Graphics - Attributes page.3. Ensure the Color is Red.4. Keep all other defaults.5. Click OK.

Adding a Simple ReceiverAttached to the Washington D.C. facility is a Hawkeye 1.6 M receiver. This receiver will accept transmissions from the GEO satellite. You need to model the Hawkeye receiver that is attached to the Washington D.C. facility.

This receiver is an omnidirectional antenna with constant gain. An omnidirectional antenna radiates uniformly in all directions. A gain of zero (0) dB is representative of a theoretical perfect receiver system.

1. Bring the Insert STK Object tool ( ) to the front.2. Select the following:


4. Select Washington.5. Click OK.6. Rename it DCReceive.

Set DCReceives PropertiesYou have a Hawkeye 1.6 receiver attached to your Washington D.C. facility. You know the parameters of the Hawkeye 1.6 receiver, specifically the G/T value of 23.7 db/K. You can set that now.

1. Select the Basic - Definition page.2. Set the following parameters:

TABLE 5. Create DCReceive

Option Value

Select an Object To Be Inserted: Receiver

Select a Method: Define Properties

If the receiver is not present in the Insert STK Object tool, use the Edit Preferences to add it to the tool.

TABLE 6. DCReceives properties

Option Value15

Type Simple Receiver Model

G/T 23.7 dB/K


3. Click OK.

The simple receiver model is convenient when you do not have all the information necessary to model the receiver in detail. Table 7 on page 16 explains the other receiver types. Take a moment to go over each type with your instructor.

Create A SatelliteYou want to surveil the northern region of South America for potential illegal activity. To do this, you will use a satellite in the geostationary orbit. You can use the Insert STK Object tool to insert the GEO satellite.

1. Bring the Insert STK Object tool ( ) to the front.

TABLE 7. Receiver types in STK

Receiver Type Definition

Simple ReceiverUser-definable specs (G/T, frequency and bandwidth), polarization, rain model and pre-receive and pre-demod gains and losses.

Cable ReceiverUser-definable specs (BER, extra cable factor, propagation speed factor)

Medium ReceiverUser-definable specs (gain, frequency, and bandwidth), system temperature, polarization, rain model, and pre-receive and pre-demod gains and loses.

Complex Receiver

User-definable specs (antenna selection and configuration, frequency and bandwidth), system temperature, polarization, rain model, and pre-receive and pre-demod gains and losses.

Multibeam Receiver

User-definable specs (selection and configuration of multiple antenna beams), system temperature, polarization (for each beam), rain model and pre-receive and pre-demod gains and losses.

Laser ReceiverOptions available for Medium Receiver model, plus receiver optics and detector parameters.

Plugin Receiver Receiver defined in user-supplied script.

The Frequency Auto Track Option (when enabled) allows a receiver to track and lock onto the transmitters carrier frequency which it is currently linking, including any Doppler shift.

The Bandwidth Auto Scale option allows the receiver to adjust its bandwidth to that of the current transmitter as you switch from one transmitter to another.16

2. Select the following:


3. Click the Insert... button.4. Rename the satellite S_AmGEO.5. Select the Basic - Orbit page is selected.6. Select Lon. Ascn. Node from the RAAN drop-down menu.7. Use Table 9. Satellites properties to enter the satellites properties.

8. Click Apply.

Satellite AttitudeYou want the satellites Z axis to be aligned with the center of the earth or nadir direction, as is typical for this type of satellite. You also want to make sure the X axis is constrained in the direction of the Earth Centered Inertial (ECI) velocity vector. You have to set the attitude of the satellite to Nadir alignment with ECI velocity constraint. Lets do that now.

1. Select the Basic - Attitude page.2. Ensure Standard is selected.3. Set the Type to Nadir alignment with ECI velocity constraint.

TABLE 8. Create GEO satellite

Option Value

Select an Object To Be Inserted: Satellite


TABLE 9. Satellites properties

Option Value

Propagator Two Body

Start Time Default Scenario Start Time

End Time Default Scenario End Time

Step Size 60 sec

Orbit Epoch Default Scenario Start Time

Coord Type Classical

Coord System International Celestial Reference Frame (ICRF)

Semimajor Axis 42164.2 km

Eccentricity 0.0

Inclination 0.0

Argument of Perigee 0.0

Lon. Ascn. Node 300.0

True Anomaly 0.0 deg17

4. Ensure the Constraint offset is 0 degrees.5. Click OK.


Take a Look at Your SatelliteNow that you have modeled your satellite, lets view it in the 3D Graphics window.

1. Bring the 3D Graphics window to the front.2. Right-click on S_AmGEO ( ) in the Object Browser.3. Select Zoom To to make S_AmGEO the focal point in the 3D Graphics window.4. Mouse around the 3D Graphics window to look at the S_AmGEO satellite.

FIGURE 6. 3D View: 3D view of the S_AmGEO

Adding a TransmitterThe GEO satellite has a simple transmitter attached. This transmitter will relay information to your position in Washington D.C.



TABLE 10. Create GEO_xmit

Option Value

Select an Object To Be Inserted: Transmitter


If the transmitter is not present in the Insert STK Object tool, use the Edit Preferences to add it to the tool.18

4. Select S_AmGEO.5. Click OK.


6. Rename the transmitter GEO_xmit.

Define the Transmitter PropertiesNow that you have the transmitter attached to the GEO satellite, you can define its properties. GEO_xmit is a simple transmitter with a frequency of 12 GHz and an EIRP of 23 dBW.

1. Select the Basic - Definition page.2. Set the following parameters:

3. Click Apply.

This transmitter is an omnidirectional antenna with constant gain. An omnidirectional antenna radiates uniformly in all directions. A gain of zero (0) dB is representative of a theoretical perfect transmitter system.

The simple source transmitter model is convenient when you do not have all the information necessary to model the transmitter in detail, e.g. during the system engineering process. Take a look at Table 12. Transmitter types in STK for more transmitter types. Take a moment to go over each one with your instructor.

TABLE 11. GEO_xmit properties

Option Value

Type Simple Transmitter Model

Frequency 12 GHz

EIRP 23 dBW

Polarization Disabled

TABLE 12. Transmitter types in STK

Receiver Type Definition

Simple Source TransmitterUser-definable specs (frequency, EIRP, and data rate), polarization, post-transmit gains and losses, and modulation.

Medium Source TransmitterUser-definable specs (frequency, gain, power, data rate), polarization, post-transmit gains and losses, and modulation.

Complex Source TransmitterUser-definable specs (frequency, power, data rate, antenna selection and configuration), polarization, post-transmit gains and losses, and modulation.

Multibeam Source TransmitterUser-definable specs (selection and configuration of multiple antenna beams, data rate), post-transmit gains and losses, and modulation.

Laser Source TransmitterOptions available for Medium Source Transmitter model, plus transmitter optics parameters.19

Plug-in Source Transmitter Source transmitter defined in user-supplied script.


Modulator TabSTK/Communications allows you to select from a number of standard modulation types, analytical jammer modulation types, and to incorporate other modulation types - including your own custom types as well as several supplied with STK/Communications. In addition, you can select whether to use a CDMA (Code Division Multiple Access) spread and, if so, specify the CDMA gain by supplying a chips/bit value.

The modulation type determines two characteristics: (1) the fraction of transmitter power contained within the receivers bandwidth (computed in the Bandwidth Overlap Factor) and (2) the translation between the signal-to-noise ratio (Eb/No) and the resulting bit error rate (BER).

1. Select the Modulator tab.2. Set the Data Rate to 30 MB/Sec.3. Ensure Auto Scale Signal Bandwidth is enabled.

When Auto Scale is enabled, the transmitter adjusts its transmitting bandwidth on the basis of its data rate and the modulation type. If autoscaling is disabled, you can specify the bandwidth as symmetric (centered around the carrier frequency) or asymmetric.

4. Ensure Use CDMA Spreading is disabled.5. Ensure the Modulation Type is set to Bi Phase Shifting Keying (BPSK).6. Click OK.

Calculate the Link BudgetYou need to determine if you have acceptable link quality between the satellite transmitter and the DC receiver. To do this you will create a link budget report.

Calculating object-to-object visibility in STK is called access. STK will calculate the

Simple Re-transmitterUser-definable specs (saturation flux density, saturated EIRP), polarization, post-transmit gains and losses, and backoff and frequency transfer functions.

Medium Re-transmitterUser-definable specs (saturation flux density, gain, saturated output power), polarization, post-transmit gains and losses, and backoff and frequency transfer functions.

Complex Re-transmitter

User-definable specs (saturation flux density, saturated output power, antenna selection and configuration), polarization, post-transmit gains and losses, and back-off and frequency transfer functions.

TABLE 12. Transmitter types in STK

Receiver Type Definition20

times one object can access, or see, another object based on position and availability information that considers timing and constraints if necessary.


1. Select GEO_xmit ( ) in the Object Browser.2. Click the Access Tool button ( ) on the STK Tools toolbar.

When you open the Access tool, you can select both the object from which access will be calculated and the object(s) to which access will be calculated. The object FROM which access will be calculated is selected using the Access for: option, and all objects TO which access can be calculated is selected in the Associated Objects list. You can select the object(s) TO which youd like to calculate access be selecting them in the list.

3. Expand the Object Tree under Washington ( ).4. Select DCReceive ( ).5. Click the Link Budget... button.

What is your Carrier to Noise (C/N) ratio? Is your Bit Error Rate (BER) less than or equal to 1 e -008? Is your signal-to-noise ratio (Eb/No) between 13 to 16 dB?

The Bit Error Rate is the probability that a bit received is in error. For example, if you transmit a binary one (1) and receive a binary zero (0), a bit error has occurred. Maintaining a bit error rate of 1e-8 or less is an acceptable requirement for data reception. An Eb/No value between 13 dB and 16 dB corresponds to a BER of 1e-10 to 1e-19 for BPSK.

6. Leave the link budget report open.7. Close the Access tool.

Change BPSK to QPSKYou have received new information from your headquarters in DC. There are bandwidth limitations now imposed on your system. You need to send the same data over half the bandwidth and not interfere with adjacent frequencies. How can you acheive this? We can compare the Binary Phase Shift Keying (BPSK) with Quadrature Phase Shift Keying (QPSK) and see which modulation is best.

Binary Phase Shift Keying (BPSK) is the most fundamental of modulation schemes. It involves encoding a binary zero (0) as part of the sine wave and a binary one as an 180 degree phase shift of the same sine wave.

Quadrature Phase Shift Keying (QPSK) is an alternative modulation scheme. It involves encoding two bits: one as part of a sine wave and the other as part of a cosine wave and summing the two. This creates a savings in bandwidth over BPSK as twice the information can be represented in the same period. This also introduces complexity in the decoder at the receiver.

Lets model that in STK and see if this change affects your comm link.

1. Open GEO_xmits ( ) properties ( ).21

2. Select the Basic - Definition page.3. Select the Modulator tab.


4. Click the button in the Modulation Type field.5. Select QPSK.6. Click OK on the Select Modulation window.7. Click OK on the GEO_xmits Properties page.

Recalculate the Link Budget

1. Bring the link budget report to the front.2. Click the Refresh ( ) button.

The bandwidth in the QPSK is half the value of the bandwidth in the BPSK case. In the QPSK case, the Carrier to Noise (C/N) is equal to the signal to noise ratio (Eb/No). In the BPSK case, the C/N is three (3) dB less than the Eb/No value (or half the power). You can save bandwidth by using the QPSK over BPSK.

Does the reduction in modulation affect your comm system?

3. Close the Link Budget report.4. Save ( ) your work.

Analyzing a Dynamic PlatformYou have set up the GEO to DC communication link. You have a surveillance aircraft monitoring the distribution of weapons in South America. The aircraft needs to send the information to DC for further analysis.

The aircraft has a simple transmitter and will transmit its findings to the satellite. The satellite will then downlink to Washington D.C, which you have already determined is possible.

FIGURE 7. AWACS to DC Comm Link22

Add an E-3A Sentry AWACS AircraftLets add the aircraft that will gather intelligence on this region.


1. Select the following in the Insert STK Object tool ( ):

1. Click the Insert... button.2. Rename the aircraft Sentry_AWACS.3. Ensure the Basic - Route page is selected.4. Click the Insert Point button.5. Enter the following waypoints for the Aircraft:

6. Click the Insert Point button.7. Enter the following waypoints for the aircraft:

8. Click Apply.

Change the Aircraft ModelLets change the aircraft model to be more representative of the aircraft flying this mission.

1. Select the 3D Graphics - Model page.2. Click the button in the Model File field.3. Browse to C:\Program Files\AGI\STK 9\STKData\VO\Models\Air.4. Select the e-3a_sentry_awacs.mdl file.5. Click Open.6. Click OK.

TABLE 13. Create the aircraft

Option Value

Select an Object To Be Inserted: Aircraft


TABLE 14. Sentry_AWACS waypoint 1

Field Value

Waypoint 1 Latitude 1 deg

Longitude -77.5 deg

Altitude 29,000 ft

TABLE 15. Sentry_AWACS waypoint 2

Field Value

Waypoint 2 Latitude - 1 deg

Longitude -77.5 deg

Altitude 29,000 ft23

Take a Look at the AircraftNow that you have modeled your aircraft, lets view it in the 3D Graphics window.


1. Bring the 3D Graphics window to the front.2. Right-click on Sentry_AWACS ( ) in the Object Browser.3. Select Zoom To to make Sentry_AWACS ( ) the focal point in the 3D Graphics

window.4. Mouse around in the 3D Graphics window to get a better view of Sentry_AWACS.5. Play ( ) the animation.

FIGURE 8. 3D View: 3D view of the Sentry_AWACS

Create a Transmitter on the AircraftThe aircraft has a medium transmitter attached to it. The transmitter relays information gathered during the surveillance mission to the S_AmGeo satellite. You can use the Insert STK Object tool to create a transmitter.

1. Select the following in the Insert STK Object tool ( ):

2. Click the Insert... button.3. Select Sentry_AWACS.4. Click OK.5. Select the Basic - Definition page.6. Set the Type to Medium Transmitter Model.7. Enter the following specifications for the transmitter:

TABLE 16. Create transmitter

Option Value

Select an Object To Be Inserted: Transmitter

Select a Method: Define Properties24


8. Click Apply to accept the properties for the transmitter.9. Rename the transmitter to Air_xmit.

Modulator of Aircraft TransmitterThe commander wants to reduce cost and bandwidth. Due to the reduction in bandwidth, there are now power limitations where you can use Offset Quadrature Phase Shift Keying (OQPSK) modulation. OQPSK is the standard modulation on a transmitter attached to an aircraft. You also know the data rate is 128 kb/sec. You can set that now.

1. Select the Modulator tab.2. Set the Data Rate to 128 kb/sec.3. Change the Modulator type to OQPSK.

OQPSK uses four points equispaced around a circle. With four phases, OQPSK can encode two bits per symbol to minimize the BER - twice the rate of BPSK. Analysis shows that this may be used either to double the data rate compared to a BPSK system while maintaining the bandwidth of the signal or to maintain the data rate of BPSK, but halve the bandwidth needed.

4. Click OK.

S_AmGEO Needs a ReceiverThe S_AmGEO has a receiver that will accept transmissions from the aircraft about the location of weapons.

The medium receiver model provides more flexibility than the simple model by letting you specify the components of system temperature. The following can be set for this kind of model:

Gain - the receiver antennas isotropic gain Frequency Bandwidth System Temperature Polarization

TABLE 17. Air-xmits properties

Field Value

Frequency 14 GHz

Power 12 dBW

Gain 28 dB

Polarization Disabled25

Rain Outage


Lets change the simple receiver to a Medium Receiver.


3. Click the Insert... button.4. Select S_AmGEO.5. Click OK.6. Select the Basic - Definition page.7. Set the following options:

8. Click OK.9. Rename the satellite receiver SatRcv.

Calculate the Link BudgetLets test the quality of the link between the aircraft and the satellite. You can run a link budget report to test link quality.

1. Select Air_xmit ( ) in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.3. Expand the Object Tree under S_AmGEO ( ).4. Select SatRcv ( ).5. Click the Link Budget... button.

Is your Bit Error Rate (BER) less than or equal to 1 e -008? Is your signal-to-noise ratio (Eb/No) between 13 to 16 dB?

6. Close the link budget report.

Graph Link Budget DataYou are interested in seeing how your signal quality changes versus the frequency as the aircraft flies the surveillance mission. To do this, you will have to create a custom

TABLE 18. Create the satellite receiver

Option Value



TABLE 19. Satellite receiver settings

Option Value

Type Medium Receiver Model

Gain 37 dB26

link budget report.


1. Click the Report & Graph Manager ( ) button in the Access tool.2. Ensure the Object Type is set to Access ( ).3. Select the Acces link between Air_xmit and SatRcv. 4. Select the MyStyles directory.5. Select Create a new graph style ( ).6. Name the new report Rcvd Freq and EbNo.7. Expand the Link Information data provider.8. Move ( ) Rcvd Frequency to the Y axis.9. Move ( ) Eb/No to the Y2 axis.10. Click OK on the graph style Rcvd Freq and EbNo window.11. Click the Generate... button.12. Using the new graph, answer the following questions:

Does the received frequency fall within your receivers bandwidth?

FIGURE 9. Graph: Received Frequency and Eb/No

The receivers bandwidth is 128 kb/sec or between 13,999,936 and 14,000,064 kHz.

Save Your Work

1. Close any remaining reports.2. Close the Report & Graph Manager.3. Close the Access tool.4. Save ( ) your work.5. Leave the scenario ( ) open.6. Leave STK open( ).27

Can the Military Model Surveillance Communication in South America?28

Will Directed Antennas Help Improve Your Communication Performance?

In this exercise you will use STK and the STK/Communications module. You will look at creating antennas and customized communications plugins. Upon completion of this exercise, you will be able to:

Design a complex transmitter and receiver in STK. Point an antenna using an STK sensor as a gimbal. Take into account additional antenna gains and losses. Add STK/Communications Plugins for transmitters and receivers. Modify antenna plugins. Understand how plugins can be used to enhance the STK/Communications models.


Problem StatementThe United States military has decided to conduct an undercover surveillance operation in the northern region of South America to monitor illegal transmissions taking place between renegade militant groups distributing illegal arms. The military has ordered its group of system engineers to evaluate and create a communications system to capture data from the specified region and relay that information back to the military command and control center in Washington D.C.

Currently, you are sending communications between an aircraft to a satellite to Washington D.C. The communication link between your South American satellite and Washington D.C. is being broadcasted across many communication bands. The military is concerned about interference from other communication operations on your operation. The military wants to focus the gain of the antenna toward Washington D.C. to narrow the communication. To do that, you will add an antenna on the satellite.

This causes a redesign of the current South American communication system. You will need to add a directed antenna on your satellite. You will need to add a directed antenna on Washington D.C.


The total surveillance time is two (2) hours. You need to relay information to a facility in Washington D.C. that has a simple

receiver attached to it. You have a GEO satellite that is equipped with a complex transmitter model with

a frequency of 12 GHz and a power of 127 W. You need a parabolic antenna on the S_AmGEO satellite with a design frequency

of 12 GHz, a diameter of two (2) meters, an antenna efficiency of 55%, and a back-lobe gain of -30 db.

Washington DC has a complex receiver with a parabolic antenna and a five (5) m diameter.

SolutionUse STK/Communications module to model a scenario that can be used to conduct undercover surveillance on South America. You need to redesign the current South American communication system.

Model the World!Previously, you modeled and analyzed the initial communication links in South 30

America to determine the signal quality from a surveillance aircraft and Washington D.C. The Network_Surveillance scenario set up your initial conditions in South America


and provided a model of your communication system. You can use that as your starting point.

There is no need to change any of the scenario level properties, but you will need to save the scenario with a different name to preserve the integrity of the previously developed analysis.

1. Open the Network_Surveillance scenario if it is not already.

Before you make any more changes to the scenario, save it with a different name to preserve the integrity of the previously developed analysis.

2. Save ( ) the new scenario in the default user directory (C:\My Documents\STK 9). In doing so, create a unique folder and rename the new folder and the scenario file (*.sc) Comm_Surveillance.

Create a Link Budget ReportLets start out by creating a link budget report to see if you can improve the BER.

1. Select GEO_xmit ( ) in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.3. Select DCReceive ( ).4. Click the Link Budget... button.

How is your performance?

Using the Link Budget report, you can see that the communication between the GEO satellite and headquarters link is poor. In order to to improve performance, there are several dynamics we should consider. One way to increase performance is to add an antenna to a satellite with an increase in power. Eventually, the transmitter on the GEO satellite and the receiver at headquarters will need to be pointed toward each other for better alignment. Lets see if that can increase performance.

Adding an Antenna to the SatelliteYour communication system is currently set up like this:

If you do not have the Network_Surveillance scenario, you can open a VDF version of the completed scenario at C:\Training\Comm\Intro2Comms\Scenarios.31


FIGURE 1. AWACS to DC Comm Link

The aircraft will be monitoring the illegal transmissions and sending the information back to headquarters in DC. With the communication between the GEO satellite and the Sentry aircraft, you have excellent signal quality. However, as previously discovered, the Bit-Error-Rate (BER) between the GEO satellite and the receiver at headquarters link was poor. Due to the other military operations, you need to refine your transmission. The first approach to improving the signal is to add a directed antenna attached to the GEO satellite with increased power.

The STK/Communications module has two types of antenna objects, embedded and linked. In previous versions of STK, each antenna was created with individual property settings and the object was embedded in the receiver or transmitter properties. Now in STK 9, an antenna object may be created once and linked to a transmitter or receiver object. Lets set up an antenna.


3. Click the Insert... button.4. Select the S_AmGEO object.5. Click OK.6. Select the Basic - Definition page.7. Ensure the Type is set to Parabolic in the Antenna properties.8. Ensure the following values are set:

TABLE 1. Create antenna on S_AmGEO

Option Value

Select an Object To Be Inserted: Antenna



9. Click OK.10. Rename the antenna GEO_Antenna.

Transmitter ChangeYou just set up the satellites antenna on your satellite, but you have to make sure that the satellite transmitter is using the new antenna. To do this you will need to direct the transmitter to use the antenna by setting the transmitter to complex transmitter model and then associating it with the antenna.

The complex transmitter model allows you to select among a variety of analytical and realistic antenna models, and to define the characteristics of the selected antenna type. The following parameters can be set for this model:

Frequency - the RF carrier frequency of the transmitter Power - the RF power output of the transmitter as measured at the input to the

antenna Data rate - the data rate in the selected unit (typically megabits per second) Antenna Polarization Post-transmit Gains & Losses Modulation

1. Open GEO_xmits ( ) properties ( ).2. Change the Model Type to Complex Transmitter Model.3. Click OK on the Select Model page.4. Enter the following Model specifications:

5. Click Apply.

TABLE 2. GEO_Antennas properties

Field Value

Design Frequency 12 GHz

Diameter 2 m

Antenna Efficiency 55%

Back-lobe Gain -30 dB

TABLE 3. GEO_xmits properties

Field Value

Frequency 12 GHz

Power 127 W33


Embedded vs. Linked AntennasThere are two ways to use antennas in STK, an embedded or linked antenna. The embedded antennas are usually attached to a parent object like a receiver and/or transmitter. These antennas are specific to their parent object. This means that they can not be used by multiple objects. The properties for the antenna are set within the properties of the receiver and transmitters.

The linked antennas are independent of any receiver or transmitter and thus facilitate the sharing of the antenna by several transmitters and receivers. For example, if you have multiple transponders attached to a communication GEO satellite, you can create an antenna object and have the transmitters or receivers reference it. This is convenient when you have to change the properties of the antenna because instead of changing the properties for on each transmitter and receiver object, you only need to change the properties of one antenna.

You now need to tell the transmitter to reference the antenna attached to S_AmGEO. This means you want to use the linked antenna option.

1. Select the Antenna tab.2. Set the Reference Type to Link.3. Ensure the Antenna/GEO_Antenna as the Antenna Name.4. Click Apply.

Modulator TabYou also need to limit the bandwidth to narrow the broadcast so it does not interfere with other military broadcasts. To do this, you will change the data rate.

1. Select the Modulator tab.2. Set the following options:

Code Division Multiple Access (CDMA) is a Digital Wireless Technology developed by Department Of Defense in the 1960s. Digital Spread-Spectrum Modulation Technique is used mainly with Personal Communications Devices, such as mobile phones. In 1999, the International Telecommunications Union select CDMA as the industry standard for new third generation(3G) wireless systems.

3. Click OK to accept GEO_xmits ( ) properties ( ).

TABLE 4. GEO_xmits modulator properties

Option Value

Data Rate 30 Mb/sec

Modulation Type QPSK

Signal Bandwidth Auto Scale Enabled

CDMA Spreading Disabled34


Adding a Complex ReceiverNow that you have an antenna and transmitter system on your satellite, you need a complex receiver at your headquarters in Washington D.C. to accept the transmission from the satellite. The complex receiver offers a few more options that are customizable.

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. The following parameters can be set for this model:

Antenna Frequency Bandwidth System Temperature Polarization Rain Outage Pre-Receive & Pre-Demodulation Gains & Losses


3. Click the Insert... button.4. Select Washington.5. Click OK.6. Rename it DC_ComplexRcv.7. Select the Basic - Definition page on the properties page ( ).8. Set the Model Type to Complex Receiver Model.9. Click OK on the Select Model window.

Set the AntennaYou still havent modeled the parabolic antenna. You can set those properties now. Rather than link to an antenna like before, you will set the antenna properties in the receivers properties.

1. Select the Antenna tab.2. Set the following parameters:

TABLE 5. Create receiver on Washington

Option Value




3. Leave all other defaults.4. Click OK.

Calculate the Link BudgetYou have created a directed receiver and antenna. Lets see the effect of this on the signal quality of your link.

1. Select GEO_xmit ( ) in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.3. Select DC_ComplexRcv ( ).4. Click the Link Budget... button.

What is the BER? Is it acceptable? Why is the performance so poor?

Notice the difference in having an omni-directional receiver compared with a directed one. You think the performance of the latter link is much worse because of misalignment of the receiver and transmitter boresights due to the orbital geometry. You think the antennas are not pointed toward one another.

5. Leave the Link Budget report open.6. Close the Access tool.

Verify Performance in 3DYou just determined your directed antennas performance was terrible. What could be the cause of this? Lets create boresight vectors to see if the antenna and receiver are pointed at each other.

1. Open GEO_xmits ( ) properties ( ).2. Select the 3D Graphics - Vector page.3. Enable the Boresight Vector.4. Set the Componet Size to seven (7).5. Click OK.

TABLE 6. DC_ComplexRcvs antenna properties

Option Value

Reference Type Embed

Type Parabolic

Diameter 5 m36


Turn on DC_ComplexRcvs Boresight VectorNow that you turned on GEO_xmits boresight vector, lets turn on DC_ComplexRcvs boresight vector so you can determine if they are truly pointing at one another.

1. Open DC_ComplexRcvs ( ) properties ( ).2. Select the 3D Graphics - Vector page.3. Enable the Boresight Vector.4. Set the Componet Size to seven (7).5. Click OK.

Change Your Perspective

1. Bring the 3D Graphics window to the front.2. Click the Home View ( ) button. 3. Reset ( ) the animation to refresh the view in the 3D Graphics window.4. Mouse around the 3D Graphics window until you can clearly see the vectors.

FIGURE 2. 3D View: Non-Intersecting vectors

You can easily see that the vectors do not intersect. This is the reason your performance is so poor; the receiver and transmitter do not see one another. You will need to fix this.

Other Ways to Introduce ObjectsThe Insert STK Objects tool also provides an option to disable this feature in the event that you prefer to create and configure objects manually. If the Insert STK Objects tool were disabled, you could open that tool by either:37

Clicking the Insert Object button ( ). or


Selecting New... from the Insert menu.

If you prefer to use the Object Catalog, you can enable that tool by:

Clicking the New Object button ( ) to launch the Object Catalog.

The Object CatalogAll objects that you can add to a scenario are also found in the Object Catalog. The Object Catalog updates dynamically based on your selections in the Object Browser. When you select an object in the Object Browser, the Object Catalog will be populated with all eligible siblings and children of that object. When you introduce an object using the Object Catalog, a generic instance of that selected object is introduced into the scenario. STK configures that object using the standard default properties which vary depending on the object.38


FIGURE 3. Object Catalog

Pointing the Receiver and TransmitterYou need to point the receiver and the antenna toward one another. In STK, this is accomplished by placing the transmitter, receiver, or antenna on a sensor and manipulating the sensor. Since the antenna becomes a child of the sensor, the antenna will point anywhere the sensor points.

Lets add some sensors to visually see what is happening.

1. Select Washington ( ) in the Object Browser.2. Attach a Sensor ( ) object using the Object Catalog.39

3. Rename it Gimbal_R.


Target S_AmGEOLets point the antenna toward the S_AmGEO satellite by pointing the sensor.

1. Open Gimbal_Rs ( ) properties ( ).2. Select the Basic - Definition page.3. Set the Cone Angle to five (5) deg.4. Select the Basic - Pointing tab.5. Set the Pointing Type to Targeted.6. Move ( ) the S_AmGEO satellite to the Assigned Targets field.7. Click OK.

Add an Antenna ObjectRemember DC has a parabolic antenna with a diameter of five (5) m. You added a sensor so you could point the antenna toward the satellites transmitter. Rather than keep your receiver properties with an embedded antenna, you now want to create an antenna and link to it like you did with your transmitter. Lets create that antenna.

1. Select Gimbal_R ( ) in the Object Browser.2. Attach an Antenna ( ) object using the Object Catalog.3. Rename it DC_Antenna.4. Open DC_Antennas ( ) properties ( ).5. Select the Basic - Definition page.6. Set the Type to Parabolic.7. Set the Diameter to 5 m.8. Click OK.

Use the AntennaPreviously, you had an embedded antenna. Now that you created your antenna, you can have the receiver use it.

1. Open DC_ComplexRcvs ( ) properties ( ).2. Select the Antenna tab.3. Set the Reference Type to Link.4. Select Sensor/Gimbal_R/Antenna/DC_Antenna.5. Click OK to accept the changes made to DC_ComplexRcv.


1. Bring the 3D Graphics window to the front.2. Click the Home View ( ) button. 3. Reset ( ) the animation to refresh the view in the 3D Graphics window.40

4. Mouse around the 3D Graphics window until you can clearly see the vectors.


FIGURE 4. 3D View: Almost Intersecting Sensors

Take a closer look. It appears the satellite transmitter and the Washington receiver are pointed at each other, but while they are much closer, they are not exactly pointed at one another. Lets verify this with your link budget report.

Recalculate the Link Budget


How is your BER?

Pointing the Transmitter to the FacilityWell your BER is slightly improved, but still not that great. Lets try to direct the antenna on the satellite. First you will need a pointing mechanism on your satellite as well.

1. Select S_AmGEO ( ) in the Object Browser.2. Attach a Sensor ( ) object using the Object Catalog.3. Rename it Gimbal_T.4. Open Gimbal_Ts ( ) properties ( ).5. Set the Cone Angle to be five (5) deg.6. Select the Basic - Pointing Page.7. Set the Pointing Type to Targeted.8. Move ( ) the Washington facility to the Assigned Targets field.9. Click OK.41


Move the AntennaLets move the antenna to the targeted sensor so that it is associated with the transmitter on the new sensor.

1. Select GEO_Antenna in the Object Browser.2. Cut ( ) the GEO_Antenna ( ).3. Select the Gimbal_T sensor.4. Paste ( ) the GEO_Antenna ( ).

Use the AntennaSince you moved the antenna, you need to remind the transmitter to use it.

1. Open GEO_xmits ( ) properties ( ).2. Select the Antenna tab.3. Set the Reference Type is set to Link.4. Set the Link is set to Sensor/Gimbal_T/Antenna/GEO_Antenna.5. Click OK.


1. Bring the 3D Graphics window to the front.2. Click the Home View ( ) button. 3. Reset ( ) the animation to refresh the view in the 3D Graphics window.4. Mouse around the 3D Graphics window until you can clearly see the vectors.

FIGURE 5. 3D View: Washington and S_AmGEO Sensors

It appears that the satellite can now send communications to DC, but lets check the 42

link budget report to verify.


Calculate the Link BudgetNow that you have properly pointed the sensors, the transmitter and receivers should be able to communicate with each other. Lets take a look at your signal quality to see if it has increased.


Has the BER improved? Is it acceptable?

If you compare this report with the previous link budget report, you will see a significant difference. For example, compare the BER in each report. Without proper pointing using the parabolic antennas, the BER reads a poor value due to the inability to see each other. With proper pointing, the BER values improved.

3. Keep the most recent Link Budget report open.4. Close all other Link Budget reports.

Additional Gains and LossesThere is always some satellite communications degradation loss. For the transmitter, user-specified post-transmit gains and losses can be applied in the transmitter panel under the Additional Gains and Losses tab. For the receiver, user-specified pre-receive and pre-demodulation gains and losses can be applied in the receiver panel under the Additional Gains and Losses tab. Lets take into account these satellite degradation losses.

1. Open GEO_xmits ( ) properties ( ).2. Select the Additional Gains and Losses tab.3. Click the Add button.4. Change the Identifier name to Post-Transmit Loss. 5. Set the Gain to -1 dB. This represents a typically occurring Post-Transmit Loss.6. Click OK.

Link Budget ReportNow that you have a satellite degradation loss set on the transmitter, lets see how that effects the signal quality.


What is your Effective Isotropic Radiated Power (EIRP)?43

The C/N and Eb/No are also reduced by 1 dB from the previous analysis. Post transmit may result in a slightly worse BER.


3. Close any open reports.

What is a PluginA plugin allows a user to extend and customize the capabilities of STK by implementing a script and code at specific points within STK to be used in STK computations. These extendable points include:

STK/Communications STK/Astrogator (Engine modeling propagator modeling and attitude modeling) Access HPOP Force Modeling Vector Geometry Tool

There are two types: (i) compiled code (usually a dynamic link library) and (ii) script code. Comm plugins currently utilize only script code.

Plugin scripts have three sections. The input section which represents what is being pushed from STK to the plugin. The output section which represents what is being pushed from the plugin to STK. The final section is the equations that use the inputs to manipulate the outputs.

Custom TransmitterLets add it to your Air_xmit transmitter to customize the uplink.

1. Open Air_xmits ( ) properties ( ).2. Select the Basic - Definition page.3. Click the to change the Type.4. Select the Script Plugin RF Transmitter Model.5. Click OK.6. Click the to change the script Filename.7. Browse to C:\Training\Comm\Intro2Comms\Plugins.8. Select the VB_TransmitterModel.vbs file.9. Open the VB script in Textpad or Wordpad.

Take a look at a Plugin in TextpadYou have a plugin that gives a transmitter the ability to hop frequencies to avoid detection. Lets view it and see if it can be used in your scenario by the aircraft.

The transmitter model plugin script provides all the parameters that a transmitter needs to operate in STK like frequency, power, gain, etc. The script uses various timing and geometry inputs from STK. This particular script makes use of the range computed from the transmitter and receiver positions to compute the center frequency used in transmission.44

1. Locate the following line:


Freq = 1000 * Range

2. Change this line to read:

Freq = 500 * Range

You will notice that frequency is a function of range. This is what you want so your aircraft transmissions can avoid detection.

3. Click Save to save your changes.4. Close Textpad.5. Bring the properties for Air_xmit to the front.6. Select the VB_TransmitterModel.vbs file.7. Click Open.8. Click OK on Air_xmits ( ) properties ( ).

Custom ReceiverYou now have a transmitter that hops frequency to avoid detection. Now you need a receiver on your satellite that is able to receive this type of transmission. You need to have your receiver be in tune with the transmitter frequency because you are not interested in any other frequencies on that communication band. This will require another custom plugin.

1. Open SatRcvs ( ) properties ( ).2. Select the Basic - Definition page.3. Click to change the Type.4. Select the Script Plugin RF Receiver Model.5. Click OK.6. Click to change the script Filename.7. Browse to C:\Training\Comm\Intro2Comms\Plugins.8. Select the VB_ReceiverModel.vbs file.9. Click Open.10. Click OK to accept the changes for SatRcv.

The output parameters in these examples are hard coded as constants, but this is not a requirement. Feel free to look at this plugin in a text document.

Receiver AccessNow that you have two plugins being used, lets determine the signal quality between them.

1. Select Air_xmit ( ) in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.45

3. Select SatRcv ( ) as the Associated Object.4. Click on Link Budget... under Reports.


5. Use the report to answer the following questions:

Is the BER good? Bad?

Take a look at the Received Frequency. Do you notice the slight difference? As the range between the aircraft and satellite slightly changes, the frequency, which is a function of range, also changes. The frequency is 500 times the range.

AER Report

1. Bring the Access tool to the front.2. Click on the AER... button.

You will see the variance in range directly affects the variance in the received frequency in the Link Budget report. Lets view this data in a different way.

Custom GraphYou are using a custom transmitter and receiver model. You want to graph the range and the received frequency versus time. In order to properly graph this, you need to create a custom graph.

1. Click the Report & Graph Manager button ( ) on the STK Tools toolbar.2. Set the Object Type to Access.3. Select the Access Object for the Air_xmit transmitter to the SatRcv receiver.4. Select the MyStyles directory.5. Click the Create new graph style button ( ).6. Rename the graph Range and Rcvd Frequency vs. Time.7. Expand ( ) the Link Information data provider.8. Move ( ) Range to the Y-Axis.9. Move ( ) Rcvd. Frequency to the Y2-Axis.10. Click OK.11. Click the Generate... button.

Why is there a difference in the two graphs?46


FIGURE 6. Graph: Received Frequency vs. Time

The graphs appear to be slightly shifted from one another. This is due to the Doppler shift.

Save Your Work

1. Close all remaining reports.2. Close the Report & Graph Manager.3. Close the Access tool.4. Save ( ) your work.5. Leave the scenario ( ) open.6. Leave STK open( ).47

Will Directed Antennas Help Improve Your Communication Performance?48

Can You Determine the Effect of Polarization On Your Communication System?

In this exercise, you will use STK and the STK/Communications module. You will investigate polarization for uplink and downlink communications. Upon completion, you will be able to:

Model polarization on an uplink and downlink. Utilize a multibeam receiver.


Problem StatementThe United States military has decided to conduct an undercover surveillance operation in the northern region of South America to monitor illegal transmissions taking place between renegade militant groups distributing illegal arms. The military has ordered its group of system engineers to evaluate and create a communications system to capture data from the specified region and relay that information back to the military command and control center in Washington D.C.

Progress has been made in creating the communication system in which an aircraft captures images and relays them to a satellite, before downlinking to Washington D.C. Now you have to account for a real world condition, polarization. You need to determine the effect of polarization on the uplink and downlink for your communication system. You also might need to add in a second aircraft to help monitor the region.


The total surveillance time is two (2) hours. The polarization of the satellite transmitter is right-hand circular. You need to investigate circular vs. linear polarization for both the uplink and

downlink. Add a second identical aircraft to help monitor the region. To help handle the increase in data incoming over a larger area, your comm

system will need a multibeam receiver.

SolutionUse the STK/Communications module to model a scenario that can be used to conduct undercover surveillance on South America and help you model polarization.

Model the World!Previously, you modeled and analyzed the initial communication links in South America to determine the signal quality from a surveillance aircraft and Washington D.C. The Comm_Surveillance scenario set up your initial conditions in South America and provided a model of your communication system. You can use that as your starting point.

1. Open the Comm_Surveillance scenario if it is not already.

If you do not have the Comm_Surveillance scenario, you can open a VDF version of the completed scenario at C:\Training\Comm\Intro2Comms\Scenarios.50


Before you make any more changes to the scenario, save it with a different name to preserve the integrity of the previously developed analysis.

2. Save ( ) the new scenario in the default user directory (C:\My Documents\STK 9). In doing so, create a unique folder and rename the new folder and the scenario file (*.sc) Multi_Surveillance.

PolarizationPolarization is the condition or expression of orientation of the electromagnetic field vector with reference to the antennas orientation. To calculate the loss due to polarization mismatch, you need to compare the angle between the transmitters and receivers vertical references in the plane perpendicular to the line of sight. The resultant loss is the square of the cosine of twice the angle between the two polarization states. The polarization of the satellite transmitter would need to be measured. You will try different polarizations on the ground receiver until you match.

Set the Polarization of the TransmitterTo start you are going to set the polarization of the transmitter on S_AmGEO as right-hand circular. Lets set that now and see the effects.

1. Select GEO_xmits ( ) properties ( ).2. Select the Basic - Definition page.

TABLE 1. Polarization types

Type Description

Linear The transmitter/receiver is linearly polarized.

Right-Hand CircularThe transmitter/receiver is configured for the right-hand circular polarization.

Left-Hand CircularThe transmitter/receiver is configured for left-hand circular polarization.

Vertical

The transmitter/receiver is linearly polarized, and the electrical field is vertical with respect to the antenna. If the antenna is vertically oriented, the electrical field is aligned with it.

Horizontal

The transmitter/receiver is polarized, and the electrical field is vertical with respect to the antenna. If the antenna is vertically oriented, the electrical field is aligned orthogonal with it.

EllipticalThe receiver is elliptically polarized. The vector describing the orientation of the electrical field with reference to the antenna describes an ellipse as it rotates over time.51

3. Select the Antenna tab.4. Select the Polarization tab.


5. Enable the Use option.6. Set the Polarization type to Right-hand Circular.7. Click OK.

Set the Polarization of the ReceiverIn normal situations, your ground station may not know the polarization of a satellite. You would have to vary the polarization on the ground until you matched and had an acceptable Bit Error Rate. Lets assume you do not know your satellite has a right hand circular polarization. You will set the ground station receiver to left-hand circular and check the link budget report for the BER.

1. Open DC_ComplexRcv s( ) properties ( ).2. Select the Basic - Definition page.3. Click on the Antenna tab.4. Select the Polarization tab.5. Enable the Use option.6. Set the Polarization type to Left-hand Circular.7. Set the Cross-Pol Leakage to -60 dB. This setting accounts for the interference when

the polarization is not matched.8. Click OK.

Create the Link Budget ReportYou need to determine the effect these polarization changes have on your communication system. Your current link budget styles do not have a column that will show you the polarization efficiency. You need to create a custom report to receive this information.

1. Select the GEO_xmit ( ) transmitter in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.3. Expand Washington in the Associated Objects window.4. Select DC_ComplexRcv ( ).5. Click the Report & Graph Manager button.

Duplicate the ReportYou want to add polarization efficiency to your link budget report. Lets do that.

1. Expand the Installed Styles directory.2. Select Link Budget.3. Ensure the Show Reports option is selected.4. Click the Duplicate Style ( ) button.5. Select Link Information - Flux Density in the Report Contents window that appears.52


Note that the Link Information data providers has been expanded for you.

6. Move ( ) Polarization Effic to the Report Contents window.

Set the UnitsYou want your report to generate the polarization efficiency in a unitless ratio. Lets do that now.

1. Click the Units... button.2. Disable the Use Defaults option.3. Select the Units (units) option in the New Unit Value window.4. Click OK on the Units window.5. Click OK on the Report Style window.

Change the Name of the ReportNow that you have created a specific report to check the polarization efficiency, you need to give it a new name.

1. Select Link Budget in the My Styles folder.2. Rename the report to Link Budget -Pol.

View the Report

1. Generate the Link Budget - Pol report.

Does the receiver "see" the transmitter?

You will notice that the Polarization Efficiency equals zero (0). The complete polarization mismatch results in a BER of approximately 0.5. By not choosing the correct polarization, the receiver does not see the transmitter.

2. Keep the report open for further comparisons.3. Close the Report & Graph Manager.4. Close the Access tool.

Change the Receiver TypeYou just determined that the polarization you currently have does not work. The receiver and transmitter can not communicate with one another. Lets try a different polarization and see if you cant get the receiver to talk to the transmitter.

1. Open DC_ComplexRcv ( ) properties ( ).2. Select the Basic - Definition page.3. Select the Antenna tab.53

4. Select the Polarization tab.


Linear polarization means the receiver is linearly polarized with the electromagnetic field aligned with the reference axes.

5. Change the Polarization type to Linear Polarization.

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. The value, ranging from -9999.9 dB to -0.001 dB, reflects the performance of the user's system, where -9999.9 dB represents ideal conditions (no leakage). You want to make sure the Cross Pol Leakage is set to -60 dB.

6. Ensure Cross Pol Leakage is set to -60 dB.7. Click OK.

Recalculate the Link BudgetNow that you have changed the receivers polarization, lets rerun the Link Budget - Pol report to see if your signal quality has increased.

1. Select the Link Budget - Pol report.2. Refresh ( ) the report so that the change in Polarization can be calculated.3. Take a look at the resulting report.

What is your new polarization efficiency?

Note the Polarization Efficiency is 50%, which might result in a higher BER. But for this case, you do not see a higher BER. You will need to further improve the polarization of the receiver. While your BER is good you can be more efficient by matching polarization and thus using less power.

4. Keep the report open.

Change Receiver to RHCYou have just determined that linear polarization isnt good enough. You need to change the receivers polarization to right-hand circular polarization to test that polarization.

1. Open DC_ComplexRcvs ( ) properties ( ).2. Select the Basic - Definition page.3. Select the Antenna tab.4. Select the Polarization tab.5. Change the Polarization type to Right Hand Circular Polarization.6. Click OK.54

Recalculate the Link BudgetLets see if the right-hand circular polarization has increased your signal quality.


1. Select the Link Budget - Pol report.2. Refresh ( ) the report so that the change in Polarization can be calculated.3. Take a look at the resulting report.

What is your new polarization efficiency?

Note that having the correct polarization on both ends of the link budget is desirable. This will avoid polarization mismatch and result in the best signal quality.

4. Keep the report open.

Load the Plugin for Aircraft PolarizationYou have just figured out that your transmitter is using right-hand circular polarization on the downlink from the satellites transmitter to DCs receiver. Now you have to account for polarization on the uplink from the aircraft to the satellite.

However, instead of using trial and error to figure out the polarization, you are going to use a plugin. This plugin for the aircraft transmitter will already have the polarization set to right-hand circular.

1. Open Air_xmits ( ) properties ( ).2. Select the Basic - Definition page. The transmitter type is already set to Script

Plugin RF Transmitter Model. You just need to change your file for this transmitter.

3. Click the button to change the file.4. Browse to C:\Training\Comm\Intro2Comms\Plugins.5. Open VB_TransmitterModel.vbs file using Textpad or Wordpad.6. Find the line the following line:

returnValue(VB_TransmitterModel_outputs.PolType)

7. Ensure the PolType is set to two (2). This is the polarization for right-hand circular.

8. Save your changes.9. Close Textpad.10. Click OK on Air_xmits ( ) properties ( ).

This number comes directly from the Plugin Scripting Guide. You can find that by opening the STK Programming Interface and browsin to Extend AGI Products -> Extend the Engine -> Engine Plugin Scripts -> Plugin Scripting Guide. The information on PolTypes can be found on page 57 of the Plugin Scripting Guide.55


Edit the Receiver PluginYou need to adjust the plugin attached to the satellite receiver to account for polarization.

1. Open SatRcvs ( ) properties ( ).2. Select the Basic - Definition page.3. Ensure the Type is set to Script Plugin RF Receiver Model.4. Browse to C:\Training\Comm\Intro2Comms\Plugins.5. Right-click on the VB_ReceiverModel.vbs file.6. Open the VB script in Textpad.7. Find the line the following line:

returnValue(VB_ReceiverModel_outputs.PolType)

8. Set the PolType value to two (2). This will set the polarization to right-hand circular like the Air_xmit ( ) transmitter.

9. Save the file.10. Close Textpad.11. Select the VB_ReceiverModel.vbs file in Air_xmits properties.12. Click OK.

Link Budget ComparisonNow lets test the polarization.

1. Select the SatRcv ( ) in the Object Browser.2. Click the Access tool button ( ) on the STK Tools toolbar.3. Expand Sentry_AWACS in the Associated Objects window.4. Select Air_xmit ( ).5. Click the Report & Graph Manager button ( ) on the STK Tools toolbar.6. Generate the Link Budget - Pol report.7. Compare the Polarization efficiencies.

What is your polarization efficiency?

The polarization on the aircraft transmitter and satellite receiver are now both right hand circular. They are perfectly matched and this is why your performance is good.

8. Close the remaining reports.9. Close the Report & Graph Manager.10. Close the Access tool.

Model the Second Region56

Intelligence has revealed the sale of arms has moved to another location. The military has deployed a second surveillance aircraft to monitor the area. Lets do more


analysis and planning in STK. You can start by highlighting this second area with an area target.


3. Click the Insert... button.4. Set the Name to Surveillance_Area2.5. Click the Insert Point four (4) times. These will be the latitude and longitude

bounds of your area.6. Insert the following coordinates:

7. Click OK on the Area Target Wizard to insert your surveillance area.

Get a Better Look

1. Reset ( ) the animation.2. Right-click Surveillance_Area2 ( ) in the Object Browser.3. Select Zoom To.4. Mouse around in the window to get a better look at Surveillance_Area2 ( ).

TABLE 2. Create a second area target

Option Value

Select an Object To Be Inserted: Area Target

Select a Method: Area Target Wizard

TABLE 3. Coordinates of Surveillance_Area2

Latitude Longitude

-33 deg -70 deg

-33 deg -71 deg

-34 deg -71 deg

-34 deg -70 deg57


FIGURE 1. 3D View: 3D view of Surveillance_Area2

Add a Second AircraftYou know you have an aircraft heading to a second location where arms are being exchanged. This aircraft is very similar to the Sentry_AWACS you already have in your scenario. You can copy that aircraft you made previously in your scenario because you want to keep the transmitter and aircraft the same. You will merely edit the flight route.

1. Select Sentry_AWACS ( ) in the Object Browser.2. Click the Copy ( ) button.3. Click the Paste ( ) button to insert a second aircraft into your scenario.4. Rename the second aircraft Sentry_AWACS2.5. Open Sentry_AWACS2s ( ) properties ( ).6. Select the Basic - Route page.7. Enter the following waypoints for the Aircraft:

8. Click OK on Sentry_AWACS2 properties.

Rename the Transmitter

TABLE 4. Sentry_AWACS2 Waypoints

Field Value

Waypoint 1 Latitude 1 -33 deg

Longitude 1 -70.5 deg

Waypoint 2 Latitude 2 -34 deg

Longitude 2 -70.5 deg58

You need to rename the transmitter attached to the second aircraft. Lets do that.

1. Select Air_xmit ( ) that is attached to Sentry_AWACS2.


2. Rename it Air_xmit2.


1. Reposition the view so that Sentry_AWACS2s ( ) is the focal point in the 3D Graphics window.

2. Mouse around until you have a clear view of Sentry_AWACS2s ( ) flight.3. Reset ( ) the animation.4. Play ( ) the animation and watch as Sentry_AWACS2s ( ) travels along its path.

FIGURE 2. 3D View: 3D view of Sentry_AWACS2

Multibeam AnalysisThe Commander has requested that the engineering team also evaluate the multibeam receivers on the satellite to see if they cover a broader area in the specified region.

The multibeam receiver model allows you to set up multiple antenna beams, each with its own specifications, polarization, and orientation properties. The following parameters can be set for this model:

Multibeam Antenna Data Rate Modulation Post-Transmit Gains and Losses

Create a Multibeam Receiver59

Your S_AmGEO satellite needs to receive data from both of the aircraft for analysis. To do this you will set up a multibeam receiver.


1. Attach a second receiver ( ) to the S_AmGEO satellite using the Object Catalog.