Feko & measurments

[JGemio]

I'm triying to simulate some structures with feko, but when I compare the results with real measurements, I see significant differences, especially when I use a dielectric. (At 5Ghz, i have diferences in frecuency of 600Mhz)

I'm working with a simple monopole on a ground plane, and I have the ground plane and the bow tie manufactured on FR-4.
To feed the structure I have used a wire port that joints de ground plane with the monopole (the wire is goes across the dielectric, since I have the metalic ground plane in the lower side of the substrat.

I wold be gratefully if somebody could help me or give a clue of what i'm not doing in a proper way.

Lot's of thanks

 

[KRAIG]

Have you tried with differenet mesh sizes to see if there are any differences?

 

[JGemio]

Yes, i have tried with different mesh size, and there are small differents, but not enough to match the measurement with the simulation results.

I think that it can be a problem with the excitation. I'm using a wire port with a voltage source, and i have seen that results are very sensible to the radius of the wire. The problem is that if I use the real radius, then I have warning or errors due to the fact that the length and width of the segment are more or less the same.
I don't know exactly how to introduce the excitation correctly (especially if the substrate is thin).

If you wish, I could send the the feko file.

KRAIG, Lots of thanks

 

[KRAIG]

yeah,send me the feko file i have pm you.
Actually in real life the cable is far longer than the segment you define in the model and maybe thats the problem.
Try reducing the radius to diameter/16. or more until you get no error and check your results.Anywaysend me the specifications or the feko file

 

[KRAIG]

Ok, first of all bear in mind that the connection of the two "boards" has effect on the impedance characteristics.

The main problem is that you need to define a cable-line too small compared to the real radius.

You should try editFeko.In Edit Feko you can define various sources of excitation.One of them is a coaxial cable approximation.You DON'T actually create a cable in your model,so there is no radius/length ratio to worry about .Also you can define its radius easily so you will probably have some acurate simulation results.
Maybe this kind of source can also be used in CadFeko but i dont know how since i use only Editfeko.

The negative point is that it can be inserted only in the center of a triangle so it needs a little careful meshing.