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S Parameter of Coaxial Line

I created a simple model of coaxial line and wanted to learn about the S parameter. The line is 250 long, inner radius is 1 and outer is 2.3, unit is mm. I thought the S11 should be very low and S21 should be high enough as a waveguide, but the result of S11 is shown in .pfs and is really high (larger than -10dB). I don't exactly understand the reason, did I make a wrong model or other reason?

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

I thought maybe there are some problems with A3 card. So I tried to add A3 card in EDITFEKO. But then the configuration in CADFEKO turned into gray and can't be set any more, and it couldn't run out a result. I just don't understand how this happened. Could any one give me some help. Models are attached below

image.png.7fc3ff9fcda358927202a5f1ab666a83.png

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JIF

Hello yutourc,

Your model uses coarse meshing and I suspect that is what is introducing the errors. I would mesh finer (use at least standard or even do a fine mesh) and compare the results. As a minimum, use a finer mesh close to the ports.

But then the configuration in CADFEKO turned into gray and can't be set any more, and it couldn't run out a result. I just don't understand how this happened. Could any one give me some help. Models are attached below

This happened because when you opened EDITFEKO to edit the *.pre file, you told CADFEKO that the *.pre file will handle the solution settings and not CADFEKO. If you want to make che changes to the model in CADFEKO, you need to enable the CADFEKO solution control again (Click on the 'Enable solution' button on the Solve/Run tab of the ribbon).

Altair Forum User

Your model uses coarse meshing and I suspect that is what is introducing the errors. I would mesh finer (use at least standard or even do a fine mesh) and compare the results. As a minimum, use a finer mesh close to the ports.

But when I tried fine and standard it goes even worse as shown in the below. So I still don't know the reason.

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

What's more, I use editfeko to run the model, and there is an error shown below. I think maybe I make wrong order of the cards. Or there are other reasons?

image.png.88c0795ee35a0e3e9f513e01fe07876a.png

JIF

Regarding the S-parameter calculation for the waveguide created in CADFEKO, I can reproduce your problem in 2017.1, but the results are correct in the latest version (2017.2.5). There must have been a bug that has since been fixed. Please update your version. The results I see for coarse, standard and fine meshes are as follows (and as expected below -30 dB):

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

Regarding the problem you have in the EDITFEKO model, the A3 card is not the correct source. You should be using the AW card to create a coaxial waveguide source.

Altair Forum User

Please update your version

I‘m using the latest Student Edition of FEKO that provided from Altair HyperWorks. The link is the one that attached in the email that Altair sent me. I think that is the version of 2017.0.0, but in the email it says it is the latest version. So is there something wrong with the link, or we can't use the latest 2017.2 version of FEKO as a student license?

image.png.07a7174ef62d6fcbe4fe8fd2219ef594.png

image.png.9c0bfe22c451f3433c0256b18d6263b5.png

http://wpc.23a7.iotacdn.net/8023A7/origin2/rl/HWStudent/2017/hwFEKO2017_edu_win64.exe

And also, when you are reproducing, is there any change that you make on settings? I make the model in version 2017.0.0.

JIF

Hello yutourc,

The FEKO team did make a newer version of FEKO available, but it does not look like it was made available correctly on the website. I have followed up with the responsible teams so that the new version can be made available to you (and others). We will get back to you soon.

And also, when you are reproducing, is there any change that you make on settings? I make the model in version 2017.0.0.

I made no changes to the model. I simply remeshed (resulting mesh was the same or very similar for coarse) and ran the simulations.

Altair Forum User

The update information are as shown below. So I'm wondering maybe the original license is not useful on 2017.2.

image.png.d4860d67b28020f221ea884a2aad451f.png

JIF

The original 2017 version did not allow updating the EDU version. The 2017.2 version should allow updating. It is being made available and I'll post a link or contact you when the new version can be downloaded.