Yanay Regueiro Can you elaborate your problem ?

First you have to shift you design or plane for which you want to take DXF at z= 0 plane. Then try once again

The correct method for exporting a DXF is to design/shift the layer at zero height as Arvind Kumar above said. You need to take only one layer at a time(with all other layers removed) and then export it. Hope it helps

thanks to Arvin and Nitir Kumar for their answers but the problem is in the CST tool that deforms the image at the time of exporting it, when I tell it to export it takes points that are from the spiral but also points that are not from it , that's why it deforms me. what I would like to know why the CST does that and what solution can I give it. The image I put shows what I say

This is not any error. When u draw any curve/circle/cylinder it is never perfectly smooth, no matter how many points you define to draw the curved shape, after zooming in it will be like what is shown in your diagram. You can yourself imagine that a curve is formed by joining several points according to some formula/equation So it is not perfect round/curve

Although you may improve it by increasing the number of points

the image that I show you is at the moment of exporting the points that he takes, now what solution can I give him

You can edit the shape, in its definition just increase the number of point. and then export it again. As I already said you can improve it by defining more points but at finer level it will be like this only, so take a number that makes it good enough. And if in your simulations the result is good then after fabrication it should remain similar to that.

how can i do that ( increasing the number of points )

@Yanay You can go for fabrication with these points, since these points were available during simulations also, so I think these will not make deviation in measurements.

Moreover you are seeing the zoomed version of picture or file, that's why it's visible. I think in fabrication u will get smooth curve.

I haven't worked in CST but in HFSS when defining the equation based curve it asks for number of turns and number of points. But as I said before if you are not able to do it and your simulation results are good then after fabrication it should give similar results.