GIMROC Antenna Pattern
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.
This antenna uses a rectangular coordinate system.
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. 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. 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, specify the following:
| Field | Description |
|---|---|
| Design Frequency |
This is the frequency of the antenna. The antenna design frequency is independent of the operational frequency of a transmitter, receiver, or radar. Changing the frequency of a transmitter, receiver, or radar does not update an embedded antenna's design frequency, nor vice versa. The design frequency is solely used at antenna configuration time to compute the antenna size from its max gain or beamwidth settings. A mismatch between signal frequency and antenna design frequency typically causes performance degradation. |
| Gain Matrix Size | The GIMROC antenna type reads the antenna contour samples to create the antenna's gain pattern matrix. This matrix is kept in memory for link budget computations and the graphics display of the 3D antenna gain pattern. Even though values are interpolated as necessary, sometimes the 3D graphics display is improved by computing more data in the gain matrix. The Gain Matrix Size enables you to control the fidelity of the computation and graphics by increasing the size of the internal data matrix. Increasing the matrix size will result in higher computational time. The default value of 101 x 101 is considered acceptable for most scenarios. |
| Filename | The path and file name for the GIMROC file. |
| Reload | Reloads the antenna data from the external file. |
STK uses two successive steps to interpolate the antenna gain pattern (Natural Neighbor and bi-linear bi-variate). 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. But, this small inaccuracy can easily be compensated for by appropriate postings in the Additional Gains & Losses (STK Communications) or Other Gain/Loss (STK Radar) field. When graphing gain contours, best results are obtained by using the same number of contours with the same levels as in the original data.