CPW waveport design in feko

Srabonty Soily
Srabonty Soily Altair Community Member
edited February 20 in Community Q&A

Hi, I exported one patch antenna from cst to Feko. My antenna has no ground plane it has CPW feeding which I first modeled in CST. Now for the validation purpose I put it on Feko , I exported the model  , define all substrate material then created the CPW feeding in Feko which is different method than CST. I created Edge port in my CPW feed. Now the problem is I am getting totally different S11, like in Feko its graduatually increases above -10 dB but in cst it looks perfect. I am attaching here all of my plots and port creation figure. I think my CPW feed design is wrong thats why I am getting this weired result.

 

Thanks in advance , Can anybody help me out?

imageimage

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Best Answer

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 20 Answer ✓
    Srabonty Soily said:

    @Torben Voigt  sir where is the attached model of the SMA connector in Feko ? I can't find the attachment

    This how it looks on my screen:

    image

    Note, it's CAD data not a Feko model. You can import it in any Feko version.

Answers

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 16

    Hi Srabonty Soily,

    I also think that something is wrong with your feeding. Maybe there is a short circuit? But it's hard to tell from the pictures. Could you attach the model (.cfx) here?

    Best regards,
    Torben

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 16

    Sir, thanks for your reply. I am attaching here the cadfeko file please check this.

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 16

    Hi Srabonty,

    Is it possible that the unit was not taken into account during import? The model is only 0.0245 mm x 0.02 mm in size... Ich habe mal die global unit auf m gesetzt, das sieht dann schon realistischer aus.

    Außerdem:

    • It is not recommended to model the thickness of metal surfaces. This usually only leads to an unnecessarily large number of mesh elements. If you want to take the skin effect (e.g. with copper) into account, specify the thickness in the definition of the face properties.
      image
    • I think a groundplane is missing. Could that be?

    I'll change and simulate the model for you and get back to you later with the results.

    Best regards,
    Torben

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 16

    Sir,

      Yes, You are right that thickness of the copper is needed in CST so exported model has that thickness. Thank you so much, in that case I am attaching here the exported file  so that you can import and simulate again

    [ NO ground plane is not missing, this is the type of the antenna where ground plane is not beneath the substrate, ground here is actually two l shaped patch at the front those should be negative ground and the patch bow tie feed line is positive ground, so that two negative L shape and bow tie feed line postive all together creates CPW feeding in CST. Like two negative and one positve. But I don't know the exact method in Feko to create CPW ]

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 16

    Hi Srabonty,

    Could you check the size of the antenna in CST? And mabe also attach a picture of the excitation in CST?

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 16

    Sir,

    Here is the size, and port creation of cpw in cst I have attached the screenshot also.

     

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 16

    Hi Srabonty,

    The model seems to be very sensitive to changes in the geometry of the feed. At the moment I am doing several tests with FEM (here faster than MoM), and depending on how the excitation is modeled, the results change significantly.

    It would be interesting to know how the excitation is implemented in CST, or how it is implemented in the real antenna.

    Best regards,
    Torben

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 16
    Torben Voigt_20420 said:

    Hi Srabonty,

    The model seems to be very sensitive to changes in the geometry of the feed. At the moment I am doing several tests with FEM (here faster than MoM), and depending on how the excitation is modeled, the results change significantly.

    It would be interesting to know how the excitation is implemented in CST, or how it is implemented in the real antenna.

    Best regards,
    Torben

    Sir,

    This antenna will work with SMA connector as well, as I  don't know how to design SMA connector therefor I used CPW feed. I am sharing here the link how to create CPW feed to the antenna in CST.https://youtu.be/HZ0WiW6xz5M?si=Xdje6C1F_3PhFYGq

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 19
    Torben Voigt_20420 said:

    Hi Srabonty,

    The model seems to be very sensitive to changes in the geometry of the feed. At the moment I am doing several tests with FEM (here faster than MoM), and depending on how the excitation is modeled, the results change significantly.

    It would be interesting to know how the excitation is implemented in CST, or how it is implemented in the real antenna.

    Best regards,
    Torben

    @Torben Voigt sir, do you have any update regarding my model feed?

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 19
    Srabonty Soily said:

    @Torben Voigt sir, do you have any update regarding my model feed?

    @Srabonty Soily , I hav ecreated a model with SMA feed, see attached. I'm presently investigating if the mesh needs to be refined.

    Best regards,
    Torben

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 19
    Torben Voigt_20420 said:

    @Srabonty Soily , I hav ecreated a model with SMA feed, see attached. I'm presently investigating if the mesh needs to be refined.

    Best regards,
    Torben

    Hi @Srabonty Soily , I let AMRFEKO (auto mesh refinement tool) find the best mesh. The attachment is what I got. Seems that only small improvements can be seen with the refinements. Overall, I think that's a pretty good result. The question is, of course, how accurate the results from CST are.

    image

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 19
    Torben Voigt_20420 said:

    Hi @Srabonty Soily , I let AMRFEKO (auto mesh refinement tool) find the best mesh. The attachment is what I got. Seems that only small improvements can be seen with the refinements. Overall, I think that's a pretty good result. The question is, of course, how accurate the results from CST are.

    image

    @Torben Voigt Sir, Thank you can you kindly show your S11 in Db scale ? because the screenshot I sent you is dB scale. I can't open your file because my Feko is 2022.3 version, tyours is 2023. Can you kindly show me this S11 comparison graph in dB scale?

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 20
    Torben Voigt_20420 said:

    Hi @Srabonty Soily , I let AMRFEKO (auto mesh refinement tool) find the best mesh. The attachment is what I got. Seems that only small improvements can be seen with the refinements. Overall, I think that's a pretty good result. The question is, of course, how accurate the results from CST are.

    image

    @Torben Voigt sir

    is it above - 10 dB?

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 20
    Srabonty Soily said:

    @Torben Voigt sir

    is it above - 10 dB?

    Hi @Srabonty Soily , here are the results in dB:

    image

    The figure shows the results of CST, Feko MoM (default standard mesh and refined mesh) and Feko FEM. The strong similarity of the MoM and FEM results suggests that there must be a difference in the CST model. Or in CST, some settings were chosen that may have sacrificed accuracy in favor of speed.

    I am also attaching a simple model of an SMA connector that you can import. You have to choose Teflon from the Media Library as the inner material.

    Best regards,
    Torben

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 20
    Torben Voigt_20420 said:

    Hi @Srabonty Soily , here are the results in dB:

    image

    The figure shows the results of CST, Feko MoM (default standard mesh and refined mesh) and Feko FEM. The strong similarity of the MoM and FEM results suggests that there must be a difference in the CST model. Or in CST, some settings were chosen that may have sacrificed accuracy in favor of speed.

    I am also attaching a simple model of an SMA connector that you can import. You have to choose Teflon from the Media Library as the inner material.

    Best regards,
    Torben

    @ Torben Voigt sir thank you so much! The problem is my Feko is 2022 so I can't open your model, anyways my result seems correct 3-18 GHz that's good! I appreciate your help sir!

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 20
    Torben Voigt_20420 said:

    Hi @Srabonty Soily , here are the results in dB:

    image

    The figure shows the results of CST, Feko MoM (default standard mesh and refined mesh) and Feko FEM. The strong similarity of the MoM and FEM results suggests that there must be a difference in the CST model. Or in CST, some settings were chosen that may have sacrificed accuracy in favor of speed.

    I am also attaching a simple model of an SMA connector that you can import. You have to choose Teflon from the Media Library as the inner material.

    Best regards,
    Torben

    @Torben Voigt  sir where is the attached model of the SMA connector in Feko ? I can't find the attachment

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited February 20 Answer ✓
    Srabonty Soily said:

    @Torben Voigt  sir where is the attached model of the SMA connector in Feko ? I can't find the attachment

    This how it looks on my screen:

    image

    Note, it's CAD data not a Feko model. You can import it in any Feko version.

  • Srabonty Soily
    Srabonty Soily Altair Community Member
    edited February 20
    Torben Voigt_20420 said:

    This how it looks on my screen:

    image

    Note, it's CAD data not a Feko model. You can import it in any Feko version.

    Sir,

    Thank you! Got it!

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