Characteristic mode analysis of a patch antenna with substrate
Dear all,
I am trying to learn the correct way to simulate Characteristic mode analysis. As many works in literature use FEKO, I am also using it to replicate the results of one of the papers (YANG AND ADAMS: COMPUTING AND VISUALIZING THE INPUT PARAMETERS OF ARBITRARY PLANAR ANTENNAS). Even though they have used their own computational codes, I was hoping that their first example, a simple rectangular patch with a substrate (12 cm × 7.6 cm, h = 5 mm, Air substrate), shown in Fig. 5(a), could be easily simulated.
But when I simulated with the settings suggested in this forum before, the modal results of the CMA solver were not at all close to the results in the paper Fig. 1. I have tried both with finite and infinite substrate/ground sizes (both the CADFEKO files are attached here), but still they are not matching. I am quite sure I am making some mistakes here, so please help me here. Thank you.
Best Answers
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Hello Saurav,
Not a problem, the issue was discovered to be the frequency sampling (Sampling of 10MHz provided good results) of the model as well as the feed position (x=30mm, y=0mm) of the patch. Attached is a model that provides the correct results. The highest order modes are 1, 2, 3, 133, 149, and 308, seen below:
Additionally, here is a lua script that plots the higher modes that are greater than some threshold.
Respectfully,
Evan Urban0 -
Hello Saurav,
You should be able to see the E-Field for the modes, I am attaching my full zip file that includes a .psf file that shows the near field request for the modes. Please let me know if you are having any further issues.
Respectfully,
Evan Urban0 -
Here is an image to show the Real and Imaginary component of the first mode eigenvalue:
1
Altair Employee
Answers
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Update: I got the results by increasing the frequency points and looking into both tracked and untracked modes. As you can see in the attached picture, the modes on the right side are untracked; even if I increase multiple-fold the no of modes to calculate, these modes are still untracked. So, can you please suggest any way to work around this?
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Hello Saurav,
I can have a closer look at this for you. Are you able to share your most recent model with me?
Respectfully,
Evan Urban
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Hi Evan,
Thank you for your response. Yes, it indeed is the most recent file.
Regards
Saurav
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Hi Evan,
Sorry for the mistake; I think the frequency settings were not updated in the previous file.
Please find it here.
With regards
saurav
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Hello Saurav,
Not a problem, the issue was discovered to be the frequency sampling (Sampling of 10MHz provided good results) of the model as well as the feed position (x=30mm, y=0mm) of the patch. Attached is a model that provides the correct results. The highest order modes are 1, 2, 3, 133, 149, and 308, seen below:
Additionally, here is a lua script that plots the higher modes that are greater than some threshold.
Respectfully,
Evan Urban0 -
Hi Evan,
Thank you so much for the script and the introduction of the probe. I was also looking into the nearfield-E field, but it seems they are calculated only for the no of modes calculated (10 here), unlike the case of the eigenmodes (all tracked and untracked, 322 here). So, can you please suggest a way to get the E-fields for the important modes (what your script finds: 1, 2, 3, 133, 149, 308). If I just increase the no of modes to calculate, it takes immense time for simulation. Is there any other way? Thanks again.
With regards
Saurav
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Hello Saurav,
You should be able to see the E-Field for the modes, I am attaching my full zip file that includes a .psf file that shows the near field request for the modes. Please let me know if you are having any further issues.
Respectfully,
Evan Urban0 -
Hi Evan,
Yes, I can find the fields now. I don't know how I missed it. Thank you very much for all the help.
Regards
Saurav
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Hi Evan,
@Evan_Urban I have one more follow-up question. While processing the eigenvalues, I noticed that they are always positive, which is contrary to the expected results. Even the Yang and Adams paper mentions that: 'All the resonant
modes excited by the current filament have negative λm
below resonance frequency and positive λm above resonance
frequency.' Is it because of any simulation mistake I made, or are you getting the same?With regards
Saurav
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Hi Saurav,
I will look into this and reach back out. Apologize for the delayed response I was away on leave.
Respectfully,
Evan1 -
Hi Evan,
No problem, but I have found that the .out file contains the eigenvalues in complex format with proper signs; only when I try to plot it with the postface template does the sign vanish. I guess, somehow, it is plotting only the absolute values.
Regards
Saurav
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Hi Saurav,
I see, yes in POSTFEKO I believe we were plotting the magnitude. I can adjust things quickly and show how to plot those complex formats for you, should be in Quantity Window to adjust that component.
Respectfully,
Evan0 -
Here is an image to show the Real and Imaginary component of the first mode eigenvalue:
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Hi Evan,
I got it now; thanks a lot for your prompt reply.
Regards
Saurav
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Great! not a problem, glad I could help.
Respectfully,
Evan0
