External and Plugin Models
STK Communications and STK Radar include several antenna models based on external files. Descriptions of these antenna models are in the sections below.
ITU GIMROC Antenna Files (Communications)
Options for modeling ITU antenna types is significantly enhanced by the option of reading files from the ITU-R GIMROC software package and incorporating them into STK Communications as analytical tools.
GIMROC (Space Graphical Data on CD-ROM) is available as part of the Space Radiocommunications Stations CD-ROM, published by the ITU Radio Communications Bureau.
You can read in two GIMROC file formats corresponding to:
- Earth Station Antenna Radiation Pattern
- Antenna Gain Contours Diagram
The ITU GIMROC package produces gain contour values with 0 dB as the maximum at the beam boresight. You may need to change beam and contour gain values in the gain contour text files to correspond to the gain of the real antennas of interest.
STK samples antenna gain contours on the surface of the Earth and uses the samples to generate a 3D antenna gain pattern beam. You can then use this 3D beam like any other antenna modeled analytically, such as a parabolic, Gaussian, square horn, or helix antenna. To select a GIMROC antenna file, enter its file name in the Gimroc Antenna Parameters window or click () and browse for a file.
You may lose a small amount of accuracy while generating a 3D antenna gain beam from 2D contour diagrams. This is due to the sparse, irregularly spaced data points and the interpolation algorithm. Yet, you can compensate for this small inaccuracy by including appropriate postings in the Additional Gains & Losses (Communications) or Other Gain/Loss (Radar) field. See the technical notes for further information.
Intelsat Antennas (Communications)
The gain for an Intelsat antenna is determined from data stored in an external file in a format commonly used by Intelsat. Enter the path and file name or click to browse for a file.
The format of the external file follows.
| Line | Name | Representation | Units |
|---|---|---|---|
|
Line 1 |
Series |
integer |
-- |
| Beam | string | -- | |
| Frequency | double | MHz | |
| Beam_Theta | double | degrees | |
| Beam_Phi | double | degrees | |
| Line 2 | Description | string | -- |
| Line 3 | Start_Phi | double | degrees |
| End_Theta | double | degrees | |
| End_Phi | double | degrees | |
| Start_Theta | double | degrees | |
| Num_Phi | integer | -- | |
| Num_Theta | integer | -- | |
| Line 4 and subsequent lines | <gain matrix values>
Two or more values per line is allowed. |
double | dB |
Remcom UAN Format
The gain and polarization for a Remcom UAN antenna is determined from data stored in an external file in a format that conforms to the antenna data produced by Remcom's XFdtd program. See this sample file for an example of the Remcom UAN antenna file format.
For this format, you can specify a single gain scale factor that STK will apply to the data in the external file. To do this, go to the receiver or transmitter properties, select the Basic > Definitions page, click the Antenna tab, and click the Model Specs tab. Enter a value (in dB) in the text box next to User Gain Factor. This is useful when the STK-computed gain values may not match gain values produced by other programs.
ANSYS FFD Format
You can define an antenna using an ANSYS FFD Format file. Use the ANSYS HFFS tool to generate and export one or more antenna design files. You can then load these files into STK’s ANSYS FFD Format antenna type by selecting either an FFD file or an XML file from the exported collection of files.
The XML file contains the metadata of the antenna design, such as the number of elements, the reference location of the element(s), the file name which contains the fair field electric field vectors, and the frequency dependent antenna port incident powers. The port powers incorporate various losses within the HFSS design, such as antenna impedance, antenna connection (or mismatch loss), etc.
The other file is an FFD file that contains the frequency-dependent far-field electric field vectors for an antenna element. The Far Field Data file (*.ffd) is required, while the Metadata file (*.xml) is optional. However, if the Metadata file is not present, the gain may be slightly offset in magnitude because it will default to a port incident power reference of 1 W and thus the gain will not reflect HFSS antenna design losses. These aspects are only reflected in the XML file. When the Metadata file is not present, you can correct for these missing losses by entering a value (in dB) in the field called User Gain Factor.
Input parameters for the Ansys FFD Format antenna include:
| Parameter | Description |
|---|---|
| Design Frequency | Enter the design frequency for the antenna gain pattern. |
| Defined Frequencies | List all the frequencies in the file that include a far-field pattern. |
| External Filename | Select either an HFSS-exported antenna FFD file or the XML file. |
| Gain Type | This determines if the gain pattern should be the realized gain pattern or the total gain. If you load an XML file, the selection of Total Gain or Realized Gain will utilize the accepted power or incident power from within the file. These power values incorporate various losses like coupling loss from within the HFSS antenna design. If you load an FFD file, this field is inactive because only an XML file captures this metadata. |
| Defined Power Value | This is either the accepted power or incident power within the XML file as determined by the Gain Type field. If you load an FFD file, then this value will default to 1 W because only an XML file captures this metadata. |
| User Gain Factor |
You can use this to artificially offset the magnitude of the entire gain pattern. See these sample files for examples of the Complex ANSYS HFSS Far Field Data file format: |
Ticra GRASP Antenna data format
STK Comm & Radar antennas support the "Ticra GRASP Antenna" data format. The gain pattern data is in a complex data format with each value being in real and imaginary parts. The format defines several coordinate frame types and E-Field data orthogonal pairs. Current implementation of the format in STK supports the following subset of the coordinate frames and the E-Field orthogonal pairs. The data may be represented on a "UV Grid" or "Elevation Over Azimuth" coordinate frame. The E-Field polarization orthogonal pairs may be (Right-Hand Coordinate & Left-Hand Coordinate) or Linear. Please refer to the Ticra GRASP format description for coordinate frame details.
For this format, you can specify a single gain scale factor that STK will apply to the data in the external file. To do this, go to the receiver or transmitter properties, select the Basic > Definitions page, click the Antenna tab, and click the Model Specs tab. Enter a value (in dB) in the text box next to User Gain Factor. This is useful when the STK-computed gain values may not match gain values produced by other programs.
External Antennas
The external antenna type is for antenna files arranged in a format used by STK.
In the File field, enter the name of the file containing the antenna gain data. If you are unsure of the location of the file, click to browse for the file of interest. If you are using an External antenna file with a symmetric pattern, you may specify the order of interpolation for the Mth order Lagrange interpolation algorithm. The value may range from 1 to 7, with 3 as the default if no value is specified or if the value is out of range.
Interpolation is used to calculate points between the values you specified in the input file for a symmetric pattern. 2D bivariable interpolation is used for 2D gain data on a regularly spaced grid, and the order of interpolation is linear.
Custom Gain Plugin
An interface is provided for adding your own dynamic antenna gain models. You can write the models in MATLAB or VBScript.
The required inputs and expected outputs of this model are listed below:
Custom Gain Plugin Inputs
Provide the following inputs to the script:
| Input | Description |
|---|---|
| EpochSec | A double representing the scenario simulation epoch time in seconds |
| DateUTC | A string representing the current date and time |
| CbName | A string representing the scenario central body |
| Frequency | A double representing the frequency in Hz; the current frequency at which antenna gain is desired |
| AntennaPosLLA | A vector of doubles with a length of 3; represent Latitude (degrees), Longitude (degrees), and Altitude (meters) of the antenna above the surface of the Earth |
| AzimuthAngle | The azimuth angle measured from the boresight of the antenna; represents the direction of the communications link where the gain value is required |
| ElevationAngle | The elevation angle measured from the boresight of the antenna; in combination with the azimuth angle, represents the direction of the communications link |
The above angles are measured from the boresight of the antenna and are in the antenna Polar Coordinate System used by STK.
Custom Gain Plugin Outputs
The following outputs are expected from the script by STK:
| Output | Description |
|---|---|
| AntennaGain | This is the antenna gain value in the direction given by the azimuth and elevation angles; value is in dBi. |
| AntennaMaxGain | This is the maximum gain of the antenna beam; the maximum value may be at the boresight. |
| Beamwidth | This is the 3dB beamwidth of the antenna gain pattern. |
| IntegrateGain | This is the antenna integrated gain over a noise source; STK estimates it's value using internal numerical methods. |
| DynamicGain | Displays a new 3D volume and 2D contour at each time step. Setting DynamicGain will incur a greater performance penalty due to increased graphics computations. Valid values are 1 to enable DynamicGain and 0 to disable it. |