Negative Power Loss of Dielectric

Yasaman
Yasaman New Altair Community Member
edited October 2020 in Community Q&A

Hi, Everyone!
I am new to Feko and Antenna Design in general. I am trying to model a simple turnstile antenna for a 1-Unit CubeSat, which then I am going to build using tape-measure (as conductors of turnstile antenna) and a PCB in the middle for feed circuit.

here is a link where you can learn more about CubeSats (if needed):
https://www.isispace.nl/cubesats/

 

When I model the antenna in Feko, there's always at least one dielectric region that has negative power loss in *.out file.

For example, when I model the antenna without metallic body of CubeSat, image 1 shows the negative power loss in *.out file and image 2 shows the far field pattern.

When I add the metallic body, images 3 and 4 show the results.

I have also attached my CAD files.


Can you tell me why this negative power loss happens and how can I fix it?

And also, what other ways can I use to validate my results? Since, radiation pattern in image 4 doesn't seem correct to me :)/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />

Thank you very much, 
Yasaman Parhizkar

 

 

 

 

 

 

 

 

 

<?xml version="1.0" encoding="UTF-8"?>1.PNG

<?xml version="1.0" encoding="UTF-8"?>2.PNG

<?xml version="1.0" encoding="UTF-8"?>3.PNG

<?xml version="1.0" encoding="UTF-8"?>4.PNG

Unable to find an attachment - read this blog

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Answers

  • Torben Voigt
    Torben Voigt Altair Community Member
    edited August 2019

    Hi @Yasaman,

    the layered dielecrics are very thin comared to the wavelength:

    <?xml version="1.0" encoding="UTF-8"?>image.thumb.png.c61cc4c496ca8580595754659c259bf7.pngimage.png.4db6062cd782b1360dbcc41fd1248b67.png   

     

    I don't think you will be successful wit MoM. It may be feasible to use FEM instead.

     

    I attach a FEM version of the model but you will need to see if reducing the mesh size of the thin dielectric layers changes the results.

    Unable to find an attachment - read this blog

  • Yasaman
    Yasaman New Altair Community Member
    edited September 2019

    Thank you very much, Torben Voigt!

    I used your corrected file and it didn't have any problems in power calculation!

    However, I didn't trust the FEM method, since it gave me very different results compared to MoM, even when I simulated a simple wire turnstile!

    So, in my next try with MoM, I moved the PCB board to provide a 1cm distance between PCB and the purple body. this time the negative loss problem was solved!

    Thank you again for your kind reply!

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