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Warning message 117: The ratio of the segment radius to length is too large

Altair Forum User

Hi expert Feko,

I would like to ask FEKO team about the warning that I received when I have tried to simulate my dipole antenna using wire port. What does the warning mean so that I can make improvements to my model to achieve the results?

Thank you,

attach is the warning message.

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Altair Forum User

Hi,

FEKO uses one dimensional mesh (segment) to solve wires. So it splits a wire to multiple segments and calculates the current distribution over each segment. segment length can be controlled by setting the mesh size and the segment radius can be controlled by setting the wire radius. As MoM formulation for wires only considers axial current (no variation in circumferential direction), the radius should be much smaller than the wavelength, for this assumption to be valid (smaller than 0.1 lambda).

One may intuitively expect that having smaller wire segment will improve the accuracy. This is correct to some extent, however the other factor that may affect the result is the ratio of wire radius to segment length. Numerical experiments have shown that good accuracy will be obtained for wire radius/segment length less than 0.1. for large ratios, current near open wire ends will present oscillatory behavior which may result in large errors

Altair Forum User

Dear Expert FEKO,

Thank you for your explanation. This means that the radius of the wire segment is different with the radius of the wire that I use as the dipole antenna?

I have attached the CADFEKO model of my design.

Hi,

FEKO uses one dimensional mesh (segment) to solve wires. So it splits a wire to multiple segments and calculates the current distribution over each segment. segment length can be controlled by setting the mesh size and the segment radius can be controlled by setting the wire radius. As MoM formulation for wires only considers axial current (no variation in circumferential direction), the radius should be much smaller than the wavelength, for this assumption to be valid (smaller than 0.1 lambda).

One may intuitively expect that having smaller wire segment will improve the accuracy. This is correct to some extent, however the other factor that may affect the result is the ratio of wire radius to segment length. Numerical experiments have shown that good accuracy will be obtained for wire radius/segment length less than 0.1. for large ratios, current near open wire ends will present oscillatory behavior which may result in large errors

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Altair Forum User

Dear Expert FEKO,

Thank you for your explanation. This means that the radius of the wire segment is different with the radius of the wire that I use as the dipole antenna?

I have attached the CADFEKO model of my design.

Hi,

FEKO uses one dimensional mesh (segment) to solve wires. So it splits a wire to multiple segments and calculates the current distribution over each segment. segment length can be controlled by setting the mesh size and the segment radius can be controlled by setting the wire radius. As MoM formulation for wires only considers axial current (no variation in circumferential direction), the radius should be much smaller than the wavelength, for this assumption to be valid (smaller than 0.1 lambda).

One may intuitively expect that having smaller wire segment will improve the accuracy. This is correct to some extent, however the other factor that may affect the result is the ratio of wire radius to segment length. Numerical experiments have shown that good accuracy will be obtained for wire radius/segment length less than 0.1. for large ratios, current near open wire ends will present oscillatory behavior which may result in large errors

Altair Forum User

Dear Expert FEKO,

Thank you for your explanation. This means that the radius of the wire segment is different with the radius of the wire that I use as the dipole antenna?

I have attached the CADFEKO model of my design.

Hi,

FEKO uses one dimensional mesh (segment) to solve wires. So it splits a wire to multiple segments and calculates the current distribution over each segment. segment length can be controlled by setting the mesh size and the segment radius can be controlled by setting the wire radius. As MoM formulation for wires only considers axial current (no variation in circumferential direction), the radius should be much smaller than the wavelength, for this assumption to be valid (smaller than 0.1 lambda).

One may intuitively expect that having smaller wire segment will improve the accuracy. This is correct to some extent, however the other factor that may affect the result is the ratio of wire radius to segment length. Numerical experiments have shown that good accuracy will be obtained for wire radius/segment length less than 0.1. for large ratios, current near open wire ends will present oscillatory behavior which may result in large errors