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Positive S11 parameters when modelling Loop antenna

Posted 2025年5月27日 GMT+8 20:32 RF & Microwave Engineering Version 5.3 2 Replies

Anish Thomas
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I am trying to model a circular loop antenna as part of learning COMSOL. For some reason no matter what parameters i change, i end up getting positive S11 parameter values.

I have tried the impedance boundary, scattering boundary, lumped port, and surface current density condition.

Am i missing any boundary condition, or other parameters?

2 Replies Last Post 2025年6月5日 GMT+8 01:05
Robert Koslover Certified Consultant
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Posted: 6 months ago 2025年5月28日 GMT+8 03:54
Updated: 6 months ago 2025年5月28日 GMT+8 03:56

S11 is a complex number. If you are plotting it, you are by default plotting the real part of it. Considered all by itself (in the absence of any other information) a positive value of the real part of S11 does not indicate that anything is necessarily wrong. That said, if you are new to using Comsol Multiphysics, you very probably have a variety of mistakes in your model anyway. You might want to consider posting your model to the forum.

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Scientific Applications & Research Associates (SARA) Inc.
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S11 is a complex number. If you are plotting it, you are by default plotting the real part of it. Considered all by itself (in the absence of any other information) a positive value of the real part of S11 does not indicate that anything is necessarily wrong. That said, if you are new to using Comsol Multiphysics, you very probably have a variety of mistakes in your model anyway. You might want to consider posting your model to the forum.
Anish Thomas
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Posted: 6 months ago 2025年6月5日 GMT+8 01:05

I've uploaded the file.

I managed to get negative S11 values. Though it doesnt seem to go as deep as the reference project suggests.

![https://gusbertianalog.com/content/images/2024/11/MEAS_ROUND_CCC.png]

https://gusbertianalog.com/loop-antenna-design/

Upon examining the lumped port dimensions, i believe the height is the distance between conductive boundaries, and the width is the perimeter of the conductive area.

I'm also not sure about how to include the surface current density, if im taking into account skin effect of copper wire. Also I'm not sure if the value is A/m or A/m^2.

I've uploaded the file. I managed to get negative S11 values. Though it doesnt seem to go as deep as the reference project suggests. ![https://gusbertianalog.com/content/images/2024/11/MEAS_ROUND_CCC.png] https://gusbertianalog.com/loop-antenna-design/ Upon examining the lumped port dimensions, i believe the height is the distance between conductive boundaries, and the width is the perimeter of the conductive area. I'm also not sure about how to include the surface current density, if im taking into account skin effect of copper wire. Also I'm not sure if the value is A/m or A/m^2.

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