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Determining Power Deposition

Posted Aug 12, 2020, 3:32 p.m. EDT RF & Microwave Engineering, Results & Visualization Version 5.4 3 Replies

Natalia Nigay Beamed Microwave Propulsion
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Hi all,

So here's my problem. I have an antenna connected to a 175 W amplifier via a waveguide. It's transmitting power to a nozzle (essentially a receiving antenna) approximately 1 m away. I am trying to determine how much power reaches the focal point of my parabolic nozzle through post processing.

I am new to COMSOL, so if anyone has any suggestions on how to do that, they would be greatly appreciated! Thanks a lot.

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Natalia
3 Replies Last Post Aug 13, 2020, 6:28 p.m. EDT
Robert Koslover Certified Consultant
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Posted: 4 years ago Aug 13, 2020, 11:20 a.m. EDT

If you have set this up correctly, your receiving antenna likely has a port (there are various kinds possible) at its feed. You can compute the power coupled into that port in various ways. Did you set up a port on your receving antenna (the thing which you have referred to as a "nozzle")?

If your receiving antenna does not have a port, then are you perhaps interested in how much power is incident upon some finite region of space (which you have called the "focal point")? There is no true "point" in space at which all the power arrives, when analyzing waves. Rather, the power arrives at (or passes through) a surface. You can compute the power density (power per area) at a point if you wish, by plotting the Poynting vector magnitude there. Or you could compute the component of that power density in a particular direction, if you prefer. Is that what you are looking for?

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
If you have set this up correctly, your receiving antenna likely has a port (there are various kinds possible) at its feed. You can compute the power coupled into that port in various ways. Did you set up a port on your receving antenna (the thing which you have referred to as a "nozzle")? If your receiving antenna does not have a port, then are you perhaps interested in how much power is incident upon some finite region of space (which you have called the "focal point")? There is no true "point" in space at which all the power arrives, when analyzing waves. Rather, the power arrives at (or passes through) a surface. You can compute the power *density* (power per area) at a point if you wish, by plotting the Poynting vector magnitude there. Or you could compute the component of that power density in a particular direction, if you prefer. Is that what you are looking for?
Natalia Nigay Beamed Microwave Propulsion
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Posted: 4 years ago Aug 13, 2020, 2:00 p.m. EDT

Hi Robert,

Thanks so much for your reply! I've tried this multiple ways -- most recently, I placed an undriven port at my receiving antenna where I'd like to determine the power. Would it be correct to look at my S21 paramater in dB to determine power gain (or in my case, loss)? I've also attached my file in case you are interested to see the setup/ how I'm using a nozzle as a receiving antenna.

Thanks, Natalia

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Natalia
Hi Robert, Thanks so much for your reply! I've tried this multiple ways -- most recently, I placed an undriven port at my receiving antenna where I'd like to determine the power. Would it be correct to look at my S21 paramater in dB to determine power gain (or in my case, loss)? I've also attached my file in case you are interested to see the setup/ how I'm using a nozzle as a receiving antenna. Thanks, Natalia

Attachments:

Robert Koslover Certified Consultant
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Posted: 4 years ago Aug 13, 2020, 6:28 p.m. EDT
Updated: 4 years ago Aug 13, 2020, 6:30 p.m. EDT

"Would it be correct to look at my S21 paramater in dB to determine power gain (or in my case, loss)?"

There is a big difference between the "gain" of an antenna and losses in transmission between two antennas, despite the fact that both may be expressed in dB. S21 as expressed in dB, with port 1 at one antenna and port 2 at the other, will tell you how much of the power radiated from one antenna was coupled into the other. Thus, S21 in dB will be a negative number, since 0dB would correspond to transmission of 100% of the power from one to the other. Similarly, -20dB would correspond to 1% of the power being coupled from one antenna to the other.

Perhaps some these links may be of interest to you: https://en.wikipedia.org/wiki/Friis_transmission_equation https://en.wikipedia.org/wiki/Antenna_gain https://en.wikipedia.org/wiki/Free-space_path_loss https://www.microwaves101.com/encyclopedias/s-parameters

-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
"Would it be correct to look at my S21 paramater in dB to determine power gain (or in my case, loss)?" There is a big difference between the "gain" of an antenna and losses in transmission between two antennas, despite the fact that both may be expressed in dB. S21 as expressed in dB, with port 1 at one antenna and port 2 at the other, will tell you how much of the power radiated from one antenna was coupled into the other. Thus, S21 in dB will be a negative number, since 0dB would correspond to transmission of 100% of the power from one to the other. Similarly, -20dB would correspond to 1% of the power being coupled from one antenna to the other. Perhaps some these links may be of interest to you: [https://en.wikipedia.org/wiki/Friis_transmission_equation ](http://) [https://en.wikipedia.org/wiki/Antenna_gain ](http://) [https://en.wikipedia.org/wiki/Free-space_path_loss ](http://) [https://www.microwaves101.com/encyclopedias/s-parameters ](http://)

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