Optimise the far fields that are solved as part of the Feko model.
On the Request tab, in the Optimisation group, click the Add goal
function icon. From the drop down list, select Far field.
Figure 1. The Create far field goal dialog.
The Focus is identified based on the label of a Far fields request
in CADFEKO or of an FF card in EDITFEKO.
The following focus types can be optimised:
E-field
The E-field focus type considers the radiated fields
associated with a specific far field solution request directly. The fields are
considered according to the settings of the far field request. For example if
only the scattered fields from a single object are requested, then only these
will be taken into account in the goal evaluation.
Directivity, Gain and Realised gain
With this focus type, only the directivity, gain or realised gain of the model
is considered. This option can only be based on a far field request where the
Calculate fields as specified option is chosen and is
independent of whether Directivity or
Gain is selected in the far field request.
Radar cross section (RCS):
This focus type is only valid for far field solutions that have been computed
with a plane wave source. The RCS focus type delivers
non-complex values (or an array of non-complex values) representing the derived
RCS (see section) according to the options set in the far field calculation
request. If no valid RCS information is found in the computation output, an
error will be generated during the goal evaluation.
Note: Fields that are requested in invalid directions (for example fields requested
below an infinite ground plane) are ignored during the Goal evaluation. If no valid
far field results with the correct request label are found in the solver output, an
error will be generated during the Goal evaluation phase of the first optimisation
iteration.
Polarisation
The Polarisation option allows the specification of the component of the far field to
be considered in the goal.
Total
For the E-field focus type, the
Total option provides a magnitude combination
of the - and -components of the far field. The total
field is calculated as:
(1)
This value is representative of the power
in the far field.
For the Directivity, Gain
and Realised gain focus types, the
polarisation-independent quantities are considered. This is the only
Polarisation option for
RCS.
Horizontal (Phi)/Vertical (Theta)
These options allow specific selection of the - and -directed components of the far field.
For the Directivity, Gain
and Realised gain focus types, only the component
of the field with the selected polarisation is used in the calculation
of the required quantity, delivering a non-complex value (or array of
non-complex values).
LHC/RHC
These options allow specific selection of the left-hand-circular and
right-hand-circular components of the far field (see section). For the
Directivity, Gain and
Realised gain focus types, only the component
of the field with the selected polarisation is used in the calculation
of the required quantity, delivering a non-complex value (or array of
non-complex values).
S/Z
These options allow specific selection of the S- or Z-polarised
components of the far field (see section ). For the
Directivity, Gain and
Realised gain focus types, only the component
of the field with the selected polarisation is used in the calculation
of the required quantity, delivering a non-complex value (or array of
non-complex values).
Axial ratio
This option is only available for the E-field
focus type. This provides the ratio between the magnitudes of the - and -directed field components (see section).
For the purposes of optimisation, an additional sign is added to the
Axial ratio value considered by the
optimiser. The sign indicates the handedness of the radiated field, with
a negative sign implying left-handedness, and a positive sign implying
right-handedness. This makes provision for the inclusion of the required
handedness directly in the Axial ratio
optimisation.
Ludwig III (Co and Cross)
These options allow specific selection of the Ludwig III
(Co) and Ludwig III (Cross)
polarised components of the far field (see section).
Add goal
function icon. From the drop down list, select 
Far field.