Within STK's Communications capability, you can employ an external antenna pattern file that contains user-defined data. The antenna data must form a rectangular matrix so that STK can process it. If the data originated from an antenna test system, the angle value may not necessarily result in a rectangular matrix; if this occurs, STK displays an error message. Inside the Pattern section are several keywords that identify the type of antenna pattern as well as other pertinent information for importing the pattern.
You CANNOT use the file extension *.antenna with an external antenna pattern file; your antenna data will fail to apply to an antenna object. AGI recommends using *.ant or *.pattern and applying the same extension for all external antenna files so that they are easy to locate.
The antenna pattern data type keyword can be one of the following:
- PhiThetaPattern
- ThetaPhiPattern
- AzElPattern
- ElAzPattern
- SymmetricPattern
Keywords are not case sensitive.
Communications keywords
| Keyword | Description |
|---|---|
| stk.v.<major release number>.<minor release number> |
Use this keyword to specify the version of STK software associated with the file formatting. You can create files in this format and import them into any STK software version at this level or higher. The version stamp must be the first line in the file. Example: stk.v.11.0 A file created in and stamped with this version could be imported into STK software version 11.0 through the most recent version. |
| PhiThetaPattern
ThetaPhiPattern AzElPattern ElAzPattern SymmetricPattern |
Choose one of these pattern type keywords to include in the pattern file. It tells STK how to interpret the pattern data; it describes the type and order of the data in the file. For more information on and samples of each type, see the later sections in this topic page. |
| IEEE1979 |
Add this keyword to extend one of the patterns you specified above. The extension enables you to specify the the external gain pattern data format to use measured antenna gain data using the IEEE1979 standard. For more information, see the IEEE1979 format description later in this topic. You cannot use this format with the SymmetricPattern type nor with the IrregDataGrid keywords. The data must be defined on a two-dimensional, uniformly spaced grid in a cartesian or polar coordinate frame. |
| Ieee1979PolRefAxis | You can use this keyword along with IEEE1979 to specify the reference axis for a polar coordinate pattern. The choices are: X-Axis, Y-Axis, and Z-Axis. |
| GainInterpolationLinearScale | This keyword tells STK to convert the gain values to linear scale before interpolation. |
| AngleUnits <Degrees | Radians> | This keyword controls whether STK interprets angle data as being in degrees or radians. If you do not provide the AngleUnit keyword, the value defaults to degrees. |
| 3dbBeamwidth <nnnn> | This is the angular width of the beam at half power relative to the maximum. Specify the value in the selected AngleUnits (see above). |
| IrregDataGrid | This is an optional parameter applicable to asymmetrical patterns only. If you add the keyword IrregDataGrid to the pattern file, you can then enter an asymmetrical antenna pattern that is on a nonuniform 2D grid in AzEl or ElAz space.
This keyword is applicable to data that is based on AzEl or ElAz rectangular coordinate (keywords AzElPattern and ElAzPattern). STK interpolates the data on the nonuniform grid onto a 2D uniform grid before calculating antenna gain for comm link budget analyses. The interpolation on the new 2D regular grid is an approximation of the gain pattern, and the results may not match the original data exactly. You cannot use this keyword with the IEEE1979 format. |
| OrderOfInterpolation <n> | This is an optional parameter applicable to symmetrical patterns only. Choose an order of interpolation value from 1 to 7. If not specified or if the specified value is out of range, it defaults to 1. |
| NumberOfPoints <nnnn> | This is an optional parameter that specifies the number of data points in the file. |
| PatternData |
Each row contains angle data, based on the pattern type, followed by the corresponding antenna gain in dBi. |
Symmetric antenna pattern format
Use this type for antenna patterns that are symmetric about the boresight of the antenna, where the gain value does not change as a function of phi (azimuth). It is commonly used to model traditional antennas, such as parabolic.
The symmetric pattern uses a polar coordinate system, with the boresight along the Z axis.
The data in a SymmetricPattern format consists of two columns. The first column is the elevation angle, and the second is the antenna gain in dBi.
Click here for a sample symmetric pattern file that approximates a Gaussian antenna with properties identical to the default Gaussian antenna model in STK Communications, i.e., antenna diameter of 1 m, aperture efficiency of 55%, and design frequency of 14.5 GHz.
PhiTheta/ThetaPhi antenna pattern format
This format is commonly used to model traditional antennas, such as parabolic. It describes the antenna gain as a function of the circumferential angle phi and the angle off the boresight, theta.
The PhiTheta/ThetaPhi antenna uses a polar coordinate system, where phi maps to azimuth and theta maps to elevation, with the boresight along the Z axis.
The data in a PhiThetaPattern format consists of three columns. The first column is the phi angle, the second is the theta angle, and the third is the antenna gain in dBi.
Click here for a sample PhiTheta/ThetaPhi pattern file that approximates a Gaussian antenna similarly to the SymmetricPattern sample, but only in quadrants 1 through 3 (0 deg <= phi <= 270 deg). In the fourth quadrant (270 deg < phi < 360 deg), the gain has been set to 0. This is done so the orientation of the antenna pattern in the antenna's body frame is evident in reports or 3D visualization.
Complex ANSYS *.ffd antenna file
There is another antenna pattern file format that uses theta and phi angles but none of the keywords specified in the previous table. You can define a Far Field Incident Wave Source as a plain text data file with a .ffd suffix. The source can be dependent on the frequency. See descriptions and sample files for these Complex ANSYS antenna file formats:
AzEl/ElAz antenna pattern format
This format is traditionally used for geostationary satellites, where positive azimuth and elevation is from the equator to the north.
The AzEl and ElAz antenna patterns use a rectangular coordinate system, with the boresight along the Z axis and the velocity vector along the Y axis. The azimuth and elevation are not specified in the usual spherical coordinate sense. In this case, the azimuth is measured in an east/west sense as you look to the subsatellite point on the equator below you, where positive azimuth is from the boresight toward the east. Elevation is measured in a north/south sense, where positive azimuth is from the boresight toward the north.
Click here for a sample AzEl pattern file that approximates a Gaussian antenna similarly to the PhiTheta/ThetaPhi sample. The gain in the fourth quadrant (Az > 0 deg, El > 0 deg) has been set to 0 to illustrate the antenna orientation.
IEEE1979 extension format
This format requires that you specify the gain as a combination of right-hand-circular polarized gain (RHC gain), left-hand-circular polarized gain (LHC), and the Tau angle (elliptical polarization tilt angle).
An example of a data row is:
Az El RHC_Gain LHC_Gain Tau Angle 45.0 22.8 14.0 3.0 32.0
The gain values are in dBs and the angles are in degrees or radians, as indicated by the AngleUnits keyword.
The gain file contains the data defined on a uniform regular grid in a cartesian or polar coordinate frame, as indicated by the PhiThetaPattern, ThetaPhiPattern, ElAzPattern, and AzElPattern keywords. The angle spacing along azimuth and elevation (phi and theta) axes does not need to be the same.
The total gain is computed as a linear sum of the two orthogonal gain values. The antenna polarization is computed from the two orthogonal polarization gain and the Tau angle value. The gain and the Tau Angle value matrices are interpolate using bivariate linear interpolation for sample points not on the grid points.
Here is an example of a ThetaPhi pattern file with the IEEE1979 designation:
stk.v.6.0
IEEE1979
ThetaPhiPattern
AngleUnits Degrees
NumberOfPoints 10000
PatternData
0.000000 0.000000 -15.800000 -13.100000 52.600460
1.000000 0.000000 -24.900000 -23.900000 69.581134
2.000000 0.000000 -12.000000 -10.500000 56.976587
3.000000 0.000000 -7.900000 -5.800000 55.059353
4.000000 0.000000 -6.300000 -3.700000 53.866485
5.000000 0.000000 -6.200000 -3.200000 52.579523
6.000000 0.000000 -7.700000 -3.500000 52.723497
7.000000 0.000000 -11.000000 -4.800000 54.915469
8.000000 0.000000 -13.600000 -6.400000 66.729959
9.000000 0.000000 -10.400000 -6.700000 70.989230
10.000000 0.000000 -7.300000 -5.500000 66.973957
11.000000 0.000000 -5.600000 -3.800000 61.690072
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Interaction between external antenna files and STK polarization settings
If you have an external antenna file with polarization defined, then the polarization data in the external file overrides the polarization settings in STK for the transmitter and receiver. If the external antenna file does not have polarization data defined, then the polarization settings in STK for the transmitter and receiver take effect.
Polarization must be enabled for both the transmitter and the receiver in STK for polarization to take effect.