How to get Characteristic modes
Altair EmployeeHi;
I want to replicate results from this paper : 'Characteristic-Mode-Based Improvement of Circularly Polarized U-Slot and E-Shaped Patch Antennas' by using Feko. Unfortunately, i can't get no satisfactory tracked characteristic modes when simulating the U-shaped patch antenna. In fact, some errors appear as 37561 and 37591. The structure is simulated from 2 GHz to 2.7 GHz. Number of frequency points is set to 200. I've chosen finer mesh. Any idea to mesh correctly the antenna and to get good tracked modes and compare it to those in figure 2 in the paper. Thanks.
Answers
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Hi Nabil, I am having a look at this. Could you please also share the reference that you mentioned?
One comment already is that there is no need to simulate the foam substrate (or at least not initially) - the permittivity is so close to vacuum that it will only have a nominal effect on the modes.
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Here is a modified model which works well and all modes are correctly tracked. I removed the foam and refined the mesh. I did not do a mesh convergence study, but rather over refined the mesh slightly, so you might be able to get the same results with a coarser mesh.
You will see that 2 modes experience modal cross avoidance (at 2.24 GHz and 2.43GHz) where the 1 mode merges into the other mode - this is easiest seen and understood by looking at the modal current distribution and increasing the frequency through the cross avoidance point.
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@Peter, Thank you for response.
Altair Forum User said:Could you please also share the reference that you mentioned?
It is attached to my reply. Sorry, i can't open the files error 17604 my CADFEKO version is older than yours. I'm using CADFEKO 2017-293043(x64).
Altair Forum User said:and increasing the frequency through the cross avoidance point
Do you mean the increase of the number of points within the bands of frequency at these points.
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Altair Forum User said:
I'm using CADFEKO 2017-293043(x64).
Please run the updater in CADFEKO and then you will be able to open the files
Do you mean the increase of the number of points within the bands of frequency at these points.
No, just change the frequency when viewing the modal surface current and you will see what happens at the cross avoidance point
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Dear Peter,
I'm going to upgrade my FEKO version and see the results. What about the mesh convergence study? Any idea?
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A mesh convergence study is not specific to CMA, involves refining the mesh and observing the results. Please search for other related posts in the forum for more detail, eg.
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Dear Peter,
I have always the same error : NOTICE 37561: Characteristic mode analysis may require a finer mesh compared to standard full-wave solution techniques, to accurately capture higher order mode behaviour. Should i refine more the mesh?
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Hi Nabil, as I commented earlier I believe that the mesh is overrefined, ie. it is not necessary to refine further. The notice that you get is a general notice for any CMA simulation that points out that it may be necessary to mesh finer than normal.
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