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Inquiry Regarding Impedance Calculation for Dipole Antenna Model

I am experiencing difficulties calculating the impedance across frequencies for a 50 cm dipole antenna model, which is covered with pure water and PVC. Despite attempting to modify the radius and mesh size of the model, I have been unable to resolve the issue.

Additionally, the following error messages appear:

The following message from the master process (MYID= 0):
ERROR 116: The ratio of the segment radius to length is too large
See also message in the output file halfsheathdipole_wire_fr_1_ada_1.out
ERROR 31061: ADAPTFEKO run will terminate now due to error in RUNFEKO

I have tried adjusting the geometric parameters and mesh segmentation of the model, but I am still unable to obtain the correct impedance values. Could you please advise on what settings or approaches might resolve this issue?

I would greatly appreciate any guidance you can provide.

Best regards,
NoYa

halfsheathdipole_wire_seawater.cfx

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Feko

Japanese

v2024.1.0

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Torben Voigt

Hi NoYa,

The wire segments are quite short compared to their radius. Feko want segments to be at least 5 time their radius, else they can#T be considered "thin wires" (rather cylinders then).

Please note also that the length of your dipole is 2*dipole_l. Is that intentional?

Apart from that, I am encountering strange behavior of the mesher, which I cannot explain at the moment. The wire parts outside the dielectric are extremely finely meshed, those inside are very large. I need to investigate this before I can offer a solution.

Best regards,
Torben

Torben Voigt

Ok, I see now that you changed the properties of freespace, so that the whole sorrounding is basically sea water. That explains the small mesh elements.

I would recommend trying without the additional PVC and purewater regions and use a mesh size of 0.01m. That seems to work. Still it's a bit difficult to mesh the wire with radius of 5mm in sea water, due to the small wavelength. Maybe you should try with a cylinder instead, see attached model. Dipole seems to resonate around 75 MHz.

I added three symmetry planes to reduce the computational cost.

Best regards,
Torben

halfsheathdipole_wire_seawater_cylinder.cfx

NoYa

Ok, I see now that you changed the properties of freespace, so that the whole sorrounding is basically sea water. That explains the small mesh elements.

I would recommend trying without the additional PVC and purewater regions and use a mesh size of 0.01m. That seems to work. Still it's a bit difficult to mesh the wire with radius of 5mm in sea water, due to the small wavelength. Maybe you should try with a cylinder instead, see attached model. Dipole seems to resonate around 75 MHz.

I added three symmetry planes to reduce the computational cost.

Best regards,
Torben

Hi Torben,

Thank you for your reply.

As you pointed out, when working in seawater, the mesh elements become very small, and with a wire radius of 0.005m, the short wavelength makes meshing difficult. Therefore, I will switch to using the cylinder model for the calculations, as you suggested.

Thank you again for your helpful advice.

Best regards,
NoYa