ITU GIMROC Antenna Files | Intelsat Antennas | External Antennas | Custom Gain Plugin

External and Plugin Models

STK Communications and STK Radar include several antenna models based on external files. These are described 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.

Two GIMROC file formats may be read in, corresponding to:

  • Earth Station Antenna Radiation Pattern
  • Antenna Gain Contours Diagram

The ITU GIMROC package outputs gain contour values with 0 dB as the maximum at the beam boresight. Users may need to modify 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. This 3D beam can then be used just as 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 the ellipsis (...) button and browse for a file.

A small amount of accuracy may be lost while generating a 3D antenna gain beam from 2D contour diagrams, due to the sparse, irregularly spaced data points and the interpolation algorithm. However, this small inaccuracy can easily be compensated for by 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 the ellipsis (...) button to browse for a file.

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, use the ellipsis (...) button to browse for the file of interest. If you are using an External antenna file with a symmetric pattern, you have the option of specifying 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 specified by the user 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. The models can be written in the MATLAB, Perl or VBScript scripting languages.

The required inputs and expected outputs of this model are listed below:

Custom Gain Plugin Inputs

The following inputs are to be provided to the script:

  • 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. This is the current frequency at which antenna gain is desired.
  • AntennaPosLLA - a vector of doubles with a length of 3. The elements of the vector 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. This represents the direction of the communications link where the gain value is required.
  • ElevationAngle - the elevation angle measured from the boresight of the antenna. This angle 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:

  • AntennaGain - the antenna gain value in the direction given by the azimuth and elevation angles. The gain value is in dBi.
  • AntennaMaxGain - the maximum gain of the antenna beam. The maximum value may be at the boresight.
  • Beamwidth - the 3dB beamwidth of the antenna gain pattern.
  • IntegrateGain - the antenna integrated gain over a noise source. This value is currently estimated by STK using internal numerical methods. Future versions will use a value supplied by the scripts.
  • 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.

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