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# Characteristic Mode Analyses, FEKO

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#### erayarik

##### Newbie level 6

How you define the best position of feeder in a rectangular patch antenna by using characteristic mode analyses. I am using FEKO and can calculate characteristic modes of the patch but ı couldnt evaluate them and find a way to use my results.

Hi erayarik,

I've never used FEKO, but I don't see how solving the characteristic modes will help you impedance match your antenna. The eigenmode solution will tell you the frequency at which the patch resonates, and possibly the quality factor of the resonance. Neither of these is terribly useful for impedance matching -- usually, one wants to look at the input impedance or return loss of the antenna from the feed line input.

erayarik

### erayarik

Points: 2

Actually it was my fault that ı couldnt explain well enough the problem. Feko is calculating characteristic modes (eigenmode and characteristic angle) and also possible current modes of the patch and the directions also. Please see the pictures below. And by looking at these currents, I could find some thesis also, one can find a possible optimum positions depends on what kind of radiation pattern you have intended to. But ı couldnt understand the relation ship between current modes and the feeder position. in FEKO seminars I also saw that, in antenna placement problems in large objects like aircraft, they use this method also to find best position for antenn on airplain body. I would be very glad if you and the other members could help me to understand this subject. Thank you very much again.

Hi erayarik,
the excitation you are using now in the pictures is a plane wave applied along your antenna structure in order to get the eigenvalues/ eigencurrents, and as far as I know the higher surface current density values indicates possible placements of the excitation.
Good luck!

thank you nano_o

Actually ı have tried this, yes you are right, for example when you put an antenna on the edges of the patch, it looks that i am getting better results but, each modes have different radiation pattern and have a different relationship with the other modes and this situation affect your performance, expecially if you planning to place two antenna on the patch.
actually ı watched this free web seminar of FEKO to understand the process, but ı have problems still. İf you are thinking to learn or use characteristic mode analyses(for the other members also) ı am suggesting to watch this. ı can not say ı am expert, so if someone understand better than me please write here thank you very much for answers.

https://web2.altairhyperworks.com/feko-webinar-recording-0

Hello,
actually I am working on the characteristic modes theory, but instead of starting from using Feko (because I don't have a license... :grinI started by Matlab.
I will be glad to share and discuss any matters about the characteristic modes.
Good luck!

erayarik

Points: 2