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Circular port excitation fails with piecewise stacked circular waveguide

Posted Aug 11, 2015, 6:09 p.m. EDT RF & Microwave Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3b 2 Replies

Martin Fertl
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Based on the "h bend waveguide 3d" model in version 4.3b I try to simulate a dielectic loaded circular waveguide geometry. The waveguide consists of three cylinders with identical inner diameter and wall thickness in series. The dielectric is not present in the attached minimal (non-)working model. The excitation frequency range is 25.3 GHz to 25.5 GHz.

To calculate the transmitted power from one end to the other I introduce a circular excitation port 1 (with arb. power of 100W) and a listener port 2. As long as I only use two stacked cylinders (Cylinder 1 and 2 or 2 and 3) in the model the excitation on port 1 works perfectly well and I obtain the expected field distribution for the excited TE11 mode.
As soon as I add a third cylinder without any gap and the same material choices as the first two cylinders and assign the excitation port to the new end face, the calculated value of the electric field is on the order of E-13 V/m instead of 5E4 V/m.

Searching the forum for "circular port" I couldn't find any answers related to my problem.
I'd appreciate any helpful comments on what is going wrong when adding the third cylinder.
2 Replies Last Post Aug 14, 2015, 8:20 p.m. EDT
Robert Koslover Certified Consultant
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Posted: 9 years ago Aug 14, 2015, 7:41 p.m. EDT
Martin,

Interesting. I opened your model and executed it with Comsol 5.1 and it worked fine. I saw what looked like a clean TE11 mode and didn't see any immediately-obvious weird behavior. So, then I opened the same file with my old copy of Comsol 4.3b, since your comment cited that, and ran it again. It gave a bad result, quite probably the same as what you saw! Maybe someone at Comsol software support should comment on this. Meanwhile, if you can, I suggest you upgrade to the newer version of the software. :)
Martin, Interesting. I opened your model and executed it with Comsol 5.1 and it worked fine. I saw what looked like a clean TE11 mode and didn't see any immediately-obvious weird behavior. So, then I opened the same file with my old copy of Comsol 4.3b, since your comment cited that, and ran it again. It gave a bad result, quite probably the same as what you saw! Maybe someone at Comsol software support should comment on this. Meanwhile, if you can, I suggest you upgrade to the newer version of the software. :)
Martin Fertl
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Posted: 9 years ago Aug 14, 2015, 8:20 p.m. EDT

Martin,

Interesting. I opened your model and executed it with Comsol 5.1 and it worked fine. I saw what looked like a clean TE11 mode and didn't see any immediately-obvious weird behavior. So, then I opened the same file with my old copy of Comsol 4.3b, since your comment cited that, and ran it again. It gave a bad result, quite probably the same as what you saw! Maybe someone at Comsol software support should comment on this. Meanwhile, if you can, I suggest you upgrade to the newer version of the software. :)


Robert,

Thanks a lot for your answer. That at least confirms for me that the model has now obvious flaws that I missed when going from two to three cylinders or that could have been introduced during troubleshooting when trying to understand what's going on here. I'm not sure if I can get hold of a newer version right now.
I'd appreciate if people at Comsol can provide a solution.

Cheers,
Martin
[QUOTE] Martin, Interesting. I opened your model and executed it with Comsol 5.1 and it worked fine. I saw what looked like a clean TE11 mode and didn't see any immediately-obvious weird behavior. So, then I opened the same file with my old copy of Comsol 4.3b, since your comment cited that, and ran it again. It gave a bad result, quite probably the same as what you saw! Maybe someone at Comsol software support should comment on this. Meanwhile, if you can, I suggest you upgrade to the newer version of the software. :) [/QUOTE] Robert, Thanks a lot for your answer. That at least confirms for me that the model has now obvious flaws that I missed when going from two to three cylinders or that could have been introduced during troubleshooting when trying to understand what's going on here. I'm not sure if I can get hold of a newer version right now. I'd appreciate if people at Comsol can provide a solution. Cheers, Martin

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