STK Communications allows you to specify an external antenna pattern file that contains user defined data. The antenna data must form a rectangular matrix in order for STK to 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.
There are no restrictions on the file extension used with the external antenna pattern file. It is recommended that you use the same extension for all antenna files so that they are easy to locate. For example, *.ant.
Depending on the type of data included in the file, the keyword can be one of the following:
Samples of the Symmetric, PhiTheta/ThetaPhi, AzEl/ElAz, and IEEE1979 antenna pattern formats are provided for your reference.
Keywords are not case-sensitive.
Communications keywords
| Keyword | Description |
|---|---|
| PhiThetaPattern
ThetaPhiPattern AzElPattern ElAzPattern SymmetricPattern |
These control the type and order of the data in the file. For example, 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. Other patterns contain similar information. Three coordinate systems are supported: Theta-Phi, Az-El, and Symmetric. Theta-Phi is a polar system where Theta is the angle off the boresight and Phi is the rotation angle about the boresight. Az-El is a rectangular system traditionally used by geostationary satellites where azimuth is measured in an east/west sense as you look to the subsatellite point on the equator below you; elevation is measured in a north/south sense. Symmetric pattern data is used for antenna patterns that are symmetric about the boresight of the antenna, where the gain value doesn't change as a function of Phi. Samples of the ThetaPhi, AzEl, and Symmetric external antenna pattern formats are provided for your reference. |
| IEEE1979 |
Extends the external gain pattern data formats to use measured antenna gain data using the IEEE1979 standard. The format requires the gain values to be Right Hand Circular polarized gain (RHC gain), Left Hand Circular Polarized gain (LHC), and the Tau angle (elliptical polarization tilt angle).
A sample of the IEEE1979 External Antenna Pattern format is provided for your reference. This format does not support the "SymmetricPattern" and the "IrregDataGrid" keywords. The data must be defined on a two-dimensional uniformly-spaced grid in a cartesian or polar coordinate frame. |
| Ieee1979PolRefAxis | This keyword can be used along with the IEEE1979 antenna pattern data format. Choices are: X-Axis, Y-Axis, or Z-Axis. |
| GainInterpolationLinearScale | This keyword converts the gain values to linear scale before interpolation. |
| AngleUnits <Degrees | Radians> | This keyword controls whether or not the angle data is interpreted as being in degrees or radians. If the AngleUnit keyword isn't found, the value defaults to degrees. |
| 3dbBeamwidth <nnnn> | Specify a value in the selected AngleUnits (see above). This is the angular width of the beam at half power relative to the maximum. |
| IrregDataGrid | This is an optional parameter applicable to non-symmetrical patterns only. The non-symmetrical antenna pattern which is on a non-uniform 2D grid in AzEl or ElAz space may be entered by specifying keyword "IrregDataGrid".
The data on the non-uniform grid is interpolated on to a 2D uniform grid before being used in antenna gain calculation 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. This keyword is applicable to data that is based on AzEl or ElAz rectangular coordinate (keyword AzElPattern/ElAzPattern). This keyword is not supported in the IEEE1979 format. |
| OrderOfInterpolation <n> | This is an optional parameter applicable to symmetrical patterns only. The input value can range 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 |
For Symmetric patterns, specify the keyword followed by the data in a 2-column format, where the 1st column corresponds to the Theta value and the 2nd column corresponds to the antenna gain in dBi. For IEEE1979 patterns, specify the keyword followed by the data in a 5-column format, where the 1st and 2nd columns correspond to the 2 pattern grid point angle values, the 3rd column corresponds to RHC gain, the 4th column corresponds to LHC gain, and the 5th column corresponds to the Tau angle. For other patterns, specify the keyword followed by the data in a 3-column format, where the 1st and 2nd columns correspond to the 2 angle values and the 3rd column corresponds to the antenna gain in dBi. |
Symmetric Antenna Pattern
This type of pattern is used for antenna patterns that are symmetric about the boresight of the antenna, where the gain value does not change as a function of Phi, and is commonly used to model traditional antennas, such as parabolic.
The symmetric antenna uses a polar coordinate system, with the boresight along the z axis.
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 External 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.
Click here for a sample PhiTheta/ThetaPhi pattern file that approximates a Gaussian antenna similarly to the SymmetricPattern sample; however, only in quadrants 1 through 3 (0 deg <= phi <= 270 deg). In the 4th 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.
AzEl/ElAz External Antenna Pattern Format
This format is traditionally used by geo-stationary satellites where azimuth is from the boresight toward the east and elevation is from the equator to the north.
the AzEl/ElAz antenna uses a rectangular coordinate system, with the boresight along the z axis.
Click here for a sample AzEl pattern file that approximates a Gaussian antenna similarly to the PhiTheta/ThetaPhi sample. Much like this other sample, the gain in the 4th quadrant (Az > 0 deg, El > 0 deg) has been set to 0 to illustrate the antenna orientation.
Sample IEEE1979 External Antenna Pattern Format
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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