There are two file formats available to provide external antenna noise temperature data:
- Symmetrical Azimuth: This format provides a symmetrical set of elevation values used over all azimuth values
- Full Azimuth/Elevation Grid: This full rectangular grid format provides the ability to uniquely describe the antenna noise over the full sphere of the antenna field of view
Both formats provide an optional header keyword "AngleUnits” which must be followed by “degrees” or “radians”. This keyword informs the parser that angle values will be interpreted as degrees or radians. If not specified, all angles are interpreted in degrees. The critical header keyword that must be provided after all other keywords is “NumberOfPoints” followed by the total number of points provided in the file. The columns of data values must follow this keyword.
Symmetrical Azimuth Format
A sample symmetrical azimuth antenna noise temperature file is provided below for your reference, where antenna noise (in Kelvin) is a function of the elevation angle. The elevation angle is measured as the angle between the detic nadir vector of the antenna's parent object and the relative position vector, minus 90 degrees. The data following the NumberOfPoints keyword consists of the elevation angle (first column) and the corresponding noise temperature in Kelvin (second column). The values must be in increasing order by elevation angle. STK interpolates the table as necessary to determine the corresponding noise temperature for a given elevation angle. If the elevation angle is less than the first point in the table, the noise temperature of the first point is used. If the elevation angle is greater than the last point in the table, the noise temperature of the last point in the table is used.
Optional Header Keywords:
InterpolationOrder: This keyword must be followed by an integer order value which allows you to specify the order of interpolation the software will use to interpolate values for azimuth/elevation value pairs between those provided in the file. The integer value provided must be greater than zero. The default value used if not provided in the file is 3.
A sample format
InterpolationOrder 1
AngleUnits degrees
NumberOfPoints 10
0.0 100.0
5.0 80.0
10.0 70.0
20.0 60.0
30.0 55.0
45.0 50.0
60.0 45.0
70.0 43.0
80.0 41.0
90.0 40.0
Full Azimuth/Elevation Grid
A sample azimuth/elevation grid antenna noise temperature file is provided below for your reference, where antenna noise (in Kelvin) is a function of both elevation and azimuth angle values. This format requires that the “AzimuthElevationGrid” keyword be provided in the header on its own line and must precede the “NumerOfPoints” keyword. If the “AzimuthElevationGrid” keyword is not provided, the data following the “NumberOfPoints” keyword will be interpreted as symmetrical data. The elevation angle is measured as the angle between the detic nadir vector of the antenna's parent object and the relative position vector, minus 90 degrees. The azimuth angle is measured as the clock angle about the positive z-axis in a north-east-down coordinate system of the antenna’s parent object from the x-axis (north) to the projection of the relative position vector into the x-y plane. The data following the NumberOfPoints keyword consists of the azimuth angle (first column), elevation angle (second column), and the corresponding noise temperature in Kelvin (second column). The data must be provided in a complete azimuth/elevation rectangular grid. If an azimuth/elevation grid point is omitted, the parser will give an error and not accept the file. If the computed azimuth or elevation value for the relative position vector is outside the values provided in the file, a noise temperature of 0 Kelvin is used for the antenna noise temperature.
A sample format
AngleUnits degrees AzimuthElevationGrid NumberOfPoints 36 0.0 -90.0 0.0 0.0 -45.0 0.0 0.0 -0.01 0.0 0.0 0.0 200.0 0.0 45.0 300.0 0.0 90.0 400.0 90.0 -90.0 0.0 90.0 -45.0 0.0 90.0 -0.01 0.0 90.0 0.0 200.0 90.0 45.0 300.0 90.0 90.0 400.0 180.0 -90.0 0.0 180.0 -45.0 0.0 180.0 -0.01 0.0 180.0 0.0 200.0 180.0 45.0 300.0 180.0 90.0 400.0 181.0 -90.0 0.0 181.0 -45.0 0.0 181.0 -0.01 0.0 181.0 0.0 0.0 181.0 45.0 0.0 181.0 90.0 0.0 270.0 -90.0 0.0 270.0 -45.0 0.0 270.0 -0.01 0.0 270.0 0.0 0.0 270.0 45.0 0.0 270.0 90.0 0.0 360.0 -90.0 0.0 360.0 -45.0 0.0 360.0 -0.01 0.0 360.0 0.0 0.0 360.0 45.0 0.0 360.0 90.0 0.0