To create a log-periodic antenna
First step : create the geometry
27 dipoles for a bandwidth from 20 to 1000 MHz
To create this relatively complex geometry, several GiD capabilities can be used.
Create a new layer : First_Branch and a second one : Second_Branch
To use a layer double-click on its name or click on its name and click on "Layer To use"
With α and L1 we determine the first monopole :
First point :
Second point :
Create a line : (-6.806, 0, 0) => (-6.806, 0, 3.93)
Scale the line with these parameters :
Next perform a rotation between the Ox axis to obtain :
The 26 successive dipoles are created using the scale function
To obtain 28 lines, erase the last one (the smallest)
This is done for the first branch.
Now change the layer to use on Second_Branch
and make a copy with a rotation around Ox axis
Uncheck 'Maintain layers'
Shift the second branch with a translation of 2,4 mm
Right-click on the GiD screen, Layer => Off => All
Switch on to the Second_Branch layer.
and move the branch towards Oy axis.
All the dipoles are created.
To create the boom, select only one branch and link it to the base of the monopole
Do not create a new point and use the right layer
The same process is used for the symmetric part
Next step is to link the two parts and create the source point at its middle
Assign the electromagnetic properties :
Generate the mesh. It may be useful to assign manually the mesh size for the smallest dipoles.
Save and launch ICARE.
The following results show what part of the antenna is active for different frequency. It is the usually operating mode of a log-periodic dipoles array.
currents at 20 MHz :
currents at 60 MHz :
currents at 200 MHz :
1 GHz (with a zoom on the smallest elements) :
Note : this result may be nicely renderer with the animate button.
The computed VSWR (sometimes called TOS in ICARE) is available in the Zin_VSWR.txt (viewed with a third party software) :
The maximum value of the computed directivity is stored in the directivity.txt file :
These results show the wideband capability of the antenna.
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