field to wire coupling

hi everyone,

i am trying to model a single wire termenated with 50 ohm impedance at both of its termenals. the wire is above a PEC ground and i use a plane wave as excitation to plot the induced current at the terminals. the problem is that this error massege always appears' knowing that i am using fine mesh' :

ERROR 39693: A cable end point should be defined within 0.2 wavelengths of a metallic triangle vertex. Please use a finer mesh around such cable end points.

and i dont know what is the 'metallic triangle vertex'.

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Feko

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Altair Forum User

Hi @MOHAMED HAMDALLA,

For cables, the underlying science requires that the cable path not is placed too far from a conducting ground plane. With your model, the implication is that a) your cable is too far from the ground plane; or b ) you need to decrease the simulation frequency (which will increase the wavelength).

I'm attaching a modified version of the model (created in CADFEKO 14.0.432). You can also see two images. One shows roughly the maximum height that is acceptable for a cable simulation. The other image shows a mesh vertex, which is just a term used to describe the corner of a mesh element. Your model uses an infinite ground plane (which isn't meshed) and that's why you don't see them. In this case, the error message might be a bit misleading.

I want to point out that you should try and keep the cable no more than 0.1*wavelength away from your conducting plane, otherwise the computational approximations might start to become less accurate.

Kind regards,

Andries

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Zakaria

andries about your help. i am now facing a big problem:

the results is not as expected and i don't know why. i am still new and i am trying to reproduce an already published results.

i just need to be sure that there is nothing wrong with my design.attached a picture of the expected results.

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JIF

I had a quick look at your model. You have provided a graph of your expected results and from that we can see the cable heights and the frequency range. What we don't have is the length, loading (from the article), excitation or the cable properties. I would like to assume that I can get these from the model that you provided and thus both sides should be loaded with 50 Ohms. But, given the fact that you decided to add an insulation on the cable that happens to have the same thickness as the cable radius, I'm a bit suspicious (could be correct, but quite a coincidence). It is even more suspicious to see that you are using 'Beeswax' for your cable insulation / coating (I have never heard of a cable with beeswax as insulation and the fact that this happens to be the first medium in the media library, makes me think that you picked a random medium). You can't expect to reproduce results if you don't model exactly the same model as your reference.

Before asking the forum for help regarding FEKO, first ensure that you have correctly created the model you are trying to compare with (correct lengths, heights, wire diameter, coating, loading and excitation). You can solve this model in MoM first (without MTL) and when you then get the correct result, you can start using the cable feature (MTL). The MoM model is simply a wire model with ports and loads and the same excitation.