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Mismatching S11 values

Posted Jun 2, 2023, 7:15 a.m. EDT RF & Microwave Engineering Version 6.0 1 Reply

Emīls Šmits
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Greetings!

I am currently working on reproducing the results of the microwave antenna model described in this study doi: 10.1063/1.4952418. Although I have tried my best to recreate geometry and material properties I seem not to be able to replicate the results obtained in mentioned study in full.

For example, although in my results the S11 curve is roughly in the same shape as one got in the study, the values of S11 in my results are significantly lower, namely S11 value of resonant frequency in the study is -5dB, and -2dB is what I achieved in my simulation.

At this moment I have tried some things but in vain. I would be very appreciative of any assistance regarding mismatching S11 values. There also is an attached model file and some result pictures.

P.S. Also I have noticed that properties of my antenna model change based on the size of the surrounding air domain, mechanism of how that could be I also don't fully understand

1 Reply Last Post Jun 2, 2023, 4:37 p.m. EDT
Robert Koslover Certified Consultant
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Posted: 11 months ago Jun 2, 2023, 4:37 p.m. EDT
  1. I don't have access to the paper you cited, but I noticed that your setting for the lumped port characteristic impedance has been left at the default value of 50 Ohms. Are you sure that's the right impedance for this port? If not, this could account for increased RF reflection. So you'll need to compute that impedance and then enter the correct value. This could be done by a study step that solves for that separately, but you might want to consider using a separate model just for that purpose, to keep things less confusing.
  2. Variations seen when changing the size of the surrounding domain are serious if the variations are serious. Consider a larger domain and/or finer mesh. Then, to save memory and computation time, consider cutting your problem space in half and using appropriate symmetry boundary conditions on the plane cut (which I believe will be a PMC, in your case).
    Good luck.
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Scientific Applications & Research Associates (SARA) Inc.
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1. I don't have access to the paper you cited, but I noticed that your setting for the lumped port characteristic impedance has been left at the default value of 50 Ohms. Are you sure that's the right impedance for this port? If not, this could account for increased RF reflection. So you'll need to compute that impedance and then enter the correct value. This could be done by a study step that solves for that separately, but you might want to consider using a separate model just for that purpose, to keep things less confusing. 2. Variations seen when changing the size of the surrounding domain are serious if the variations are serious. Consider a larger domain and/or finer mesh. Then, to save memory and computation time, consider cutting your problem space in half and using appropriate symmetry boundary conditions on the plane cut (which I believe will be a PMC, in your case). Good luck.

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