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Exciting dual antenna with two different frequencies simultaneously

Posted 2024年12月3日 GMT-5 18:32 RF & Microwave Engineering Version 6.2 3 Replies

Agathiyan Rajendran
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I am attempting to simulate the structure using COMSOL. Specifically, I am trying to excite a two-antenna array, each with four point sources, simultaneously at two different frequencies. However, I am having difficulty figuring out how to achieve this in COMSOL, as the tool is relatively new to me. I also tried combining the results of frequencies F1 and F2 in post-processing, but the outcomes seem incorrect.

Could you kindly guide me on how to approach this in COMSOL?

P.S: I mean antenna 1 with F1, and antenna 2 with F2 simultaneously.

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3 Replies Last Post 2025年1月17日 GMT-5 02:08
Robert Koslover Certified Consultant
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Posted: 2 months ago 2024年12月3日 GMT-5 19:29
Updated: 2 months ago 2024年12月3日 GMT-5 19:36

If your physics is entirely linear (and I suspect it is), then you can combine the two separately computed results just as you described, working in the frequency domain. If there are any non-linear effects of significance, then you need to do this in time domain. (Note: I am assuming you are presently attempting to do this in the frequency domain.) Now, assuming linearity holds, if the outcomes in your model "seem incorrect" to you, then: (1) there may be one or more errors somewhere in the setup of the problem, involving one or both of the two frequencies, and/or in how you endeavored to combine the results, either in post-processing or elsewhere; or (2) another possibility is that the result that concerns you may actually be correct, but is also different from what you expected. To get this resolved, I suggest you post your .mph file to the forum so that other Comsol users reading this can take a look at it and offer you suggestions specific to your model and physics.

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
If your physics is entirely linear (and I *suspect* it is), then you can combine the two separately computed results just as you described, working in the frequency domain. If there are any non-linear effects of significance, then you need to do this in time domain. (Note: I am *assuming* you are presently attempting to do this in the frequency domain.) Now, assuming linearity holds, if the outcomes in your model "seem incorrect" to you, then: (1) there may be one or more errors somewhere in the setup of the problem, involving one or both of the two frequencies, and/or in how you endeavored to combine the results, either in post-processing or elsewhere; or (2) another possibility is that the result that concerns you may actually be correct, but is also different from what you expected. To get this resolved, I suggest you post your .mph file to the forum so that other Comsol users reading this can take a look at it and offer you suggestions specific to your model and physics.
Agathiyan Rajendran
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Posted: 5 days ago 2025年1月16日 GMT-5 16:16

Thank you so much for your support.

Thank you so much for your support.
Acculution ApS Certified Consultant
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Posted: 5 days ago 2025年1月17日 GMT-5 02:08

First, you need to make sure that you actually get the mathematics of what you want to do. In the attached picture it is seemingly a 'superposition of phasors that have two slightly different frequencies', and so that suggests a sum, in which case you can do what Robert says, and run each frequency on its own and then combine studies to get the full solution. But the attached picture also mentions E_AM, suggesting Amplitude Modulation, which in turn would imply a multiplication, in which case you need a time domain solution.

Try setting up two analytical solutions in COMSOL (no FEM), and compare sin(100[Hz]t)+sin(101[Hz]t) and sin(100[Hz]t)sin(1[Hz]*t)

and look at the frequency content of each of them. I sounds like you want to do the former of the two, but make sure.

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
First, you need to make sure that you actually get the mathematics of what you want to do. In the attached picture it is seemingly a 'superposition of phasors that have two slightly different frequencies', and so that suggests a sum, in which case you can do what Robert says, and run each frequency on its own and then combine studies to get the full solution. But the attached picture also mentions E_AM, suggesting Amplitude Modulation, which in turn would imply a multiplication, in which case you need a time domain solution. Try setting up two analytical solutions in COMSOL (no FEM), and compare sin(100[Hz]*t)+sin(101[Hz]*t) and sin(100[Hz]*t)*sin(1[Hz]*t) and look at the frequency content of each of them. I sounds like you want to do the former of the two, but make sure.

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