# Far Fields (.FFE)

The data structure for the .ffe files is described.

The following fields are available in the header block:

Table 1. Fields in the header block of the .ffe file.
Key Required Description
File Type Yes Describes the type of the file. For far fields, the value must be Far Field.
File Format Yes Denotes the file syntax version (such as “4”). If not present it defaults to version 1 (files pre-dating Feko 6.1).
Source Optional Denotes the base filename of the source where this data comes from.
Date Optional Date and time of data export in format “YYYY-MM-DD hh:mm:ss” (that is 24-hour format).

The following fields are available in the solution block header:

Table 2. Available fields in the solution block header of the .ffe file.
Key Required Description
Configuration Name Optional The configuration name, if present.
Request Name Optional The explicit name given to that solution request (as denoted in the .pre file). If none is specified, POSTFEKO will use a default name of “request_N” (where “_N” is replaced with a number for each unnamed request) during import.
Frequency Yes Frequency in Hz for which the following data was measured/computed.
Coordinate System Optional Coordinate system in which the axes are defined:
• Spherical (default)
• Cartesian
Origin Optional Origin of the data coordinate system in form “(x, y, z)” (always in Cartesian coordinates; based on global origin). If no origin is provided, assume “(x, y, z)” = “(0, 0, 0)”.
U-Vector Optional Indicates a point on the U axis relative to the Origin. If none is specified, it is assumed that the U axis coincides with the X axis.
V-Vector Optional Indicates a point on the V axis relative to the Origin. If none is specified, it is assumed that the V axis coincides with the Y axis.
No. of [$$] Samples Yes The number of samples in each axis direction. The “[$$\$]” term is replaced by the following, depending on the coordinate system:
• Theta
• Phi
• U
• V
Result Type Optional For far fields (.ffe), this specifies whether the output is one of the following:
• Gain (default)
• Directivity
• RCS
• Far Field Values
Incident Wave Direction Required for RCS blocks This is a (Theta, Phi) pair indicating the angle where an infinite plane source is originating from. This field is only required if the Result Type is RCS.
Characteristic Mode Index Required for characteristic mode blocks. The value is an integer value larger than 0, which indicates the mode index of the block that follows.
Spatial Units Optional Specify the units in which the position is defined.
Result Units Optional Specify the units in which the results are given.
Efficiency Optional Specify the antenna efficiency. Only applicable when the result type is gain/directivity with the field request “total fields”.
No. of Header Lines Optional Number of header lines to read. The column header lines must follow this line. If this value is not specified, assume a value of “1”.
Yes For header lines, the following format should be used:
#No. of Header Lines: M
#"Column 1: Line 1" "Column 2: Line 1" ... "Column N: Line 1"
#"Column 1: Line 2" "Column 2: Line 2" ... "Column N: Line 2"
...
#"Column 1: Line M" "Column 2: Line M" ... "Column N: Line M"
The default column headers all have the same structure. The first two column headers depend on the coordinate system that was defined, which can be found in the Coordinate System value. The remaining column headers will depend on the far field type that was defined, which can be found in the Result type value. The column headers for each coordinate system and result type follows below.
Gain:
• Spherical coordinates:
Theta Phi Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) Gain(Theta) Gain(Phi) Gain(Total)
• Cartesian coordinates:
U V Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) Gain(Theta) Gain(Phi) Gain(Total)
Note: Gain is in dB (last three columns).
Directivity:
• Spherical coordinates:
Theta Phi Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) Directivity(Theta) ...
... Directivity(Phi) Directivity(Total)
• Cartesian coordinates:
U V Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) Directivity(Theta) ...
... Directivity(Phi) Directivity(Total)
Note: Directivity is in dB (last three columns).
RCS (that is either a bistatic or monostatic radar cross section problem):
• Spherical coordinates:
Theta Phi Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) RCS(Theta) RCS(Phi) RCS(Total)
• Cartesian coordinates:
U V Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi) RCS(Theta) RCS(Phi) RCS(Total)
Note: RCS components (last three columns) are linear. They are in m2.

Far Field Values (unknown result type, that is, the results do not pertain to an antenna problem, nor to an RCS problem):

• Spherical coordinates:
Theta Phi Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi)
• Spherical coordinates:
U V Re(Etheta) Im(Etheta) Re(Ephi) Im(Ephi)