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S-parameters

Posted Nov 4, 2014, 12:21 a.m. EST RF & Microwave Engineering Version 4.3a 3 Replies

Remmert Muller
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Hello!

I am using COMSOL RF module (emw, frequency domain) to simulate transmission line antennas. I excite my antennas using a lumped port. This is because I want to define a ground plane. Now, in the same setup I would like to incorporate ports to calculate s-parameters. These should ideally be placed between close to the lumped port and in between the lumped port and the antenna system. However, ports can only be defined on boundaries. So I am stuck here.

My question is whether both ports and lumped ports can be incorporated in the same setup in the same feeding lines. Or if it is possible to define a ground plane without using a lumped port (does port excitation off also mimics a groundplane?).

Thanks for all the help I can get! Remmert
3 Replies Last Post Nov 19, 2014, 8:57 a.m. EST
Dennis Brown
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Posted: 10 years ago Nov 5, 2014, 4:01 p.m. EST
Both ports and lumped ports allow you to get s-parameters. Lumped ports allow you to input voltages, currents, and determine input impedance (amongst other things) but ports tend to be geared towards microwave work where voltage/current are not well defined. In either case you do need a return path, you can't just hang a port out in free space.

There is an antenna model in the model gallery here. It should help you out.


www.comsol.com/model/modeling-a-dipole-antenna-8715


My question is whether both ports and lumped ports can be incorporated in the same setup in the same feeding lines. Or if it is possible to define a ground plane without using a lumped port (does port excitation off also mimics a groundplane?).


Typically if you only need one then you just use one of them. If using a coaxial port you will have a return path by its inherent nature and a uniform port needs just one return path on one of its side. Post your file or something similar and you will get a more precise answer.
Both ports and lumped ports allow you to get s-parameters. Lumped ports allow you to input voltages, currents, and determine input impedance (amongst other things) but ports tend to be geared towards microwave work where voltage/current are not well defined. In either case you do need a return path, you can't just hang a port out in free space. There is an antenna model in the model gallery here. It should help you out. http://www.comsol.com/model/modeling-a-dipole-antenna-8715 [QUOTE] My question is whether both ports and lumped ports can be incorporated in the same setup in the same feeding lines. Or if it is possible to define a ground plane without using a lumped port (does port excitation off also mimics a groundplane?). [/QUOTE] Typically if you only need one then you just use one of them. If using a coaxial port you will have a return path by its inherent nature and a uniform port needs just one return path on one of its side. Post your file or something similar and you will get a more precise answer.
Remmert Muller
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Posted: 10 years ago Nov 18, 2014, 5:58 p.m. EST
Hello Dennis Brown,

Tahnk you for the reply! It is very helpfull and I have been able to continue.

Now I am stuck at another problem. I have been trying to make my model more realistic by creating a coax. Now, however, I am stuck at selecting PEC for my boundaries. I thought that PEC boundary conditions will automatically be applied on boundaries that do not have a defined material on one side. However, this is not the case in my model. I have tried to enclose my model but unfortunately I could not.

Could you maybe help me on this?

Thanks a lot! Remmert
Hello Dennis Brown, Tahnk you for the reply! It is very helpfull and I have been able to continue. Now I am stuck at another problem. I have been trying to make my model more realistic by creating a coax. Now, however, I am stuck at selecting PEC for my boundaries. I thought that PEC boundary conditions will automatically be applied on boundaries that do not have a defined material on one side. However, this is not the case in my model. I have tried to enclose my model but unfortunately I could not. Could you maybe help me on this? Thanks a lot! Remmert
Dennis Brown
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Posted: 10 years ago Nov 19, 2014, 8:57 a.m. EST
It would be easier if you could post your file or something similar if it is proprietary. It is easy enough to post as you can delete any solutions to reduce size. Screen shots may be helpful but the actual file would be better. Just attach the file.

PECs may not always be defined as default boundaries. It depends on the overall geometry.
It would be easier if you could post your file or something similar if it is proprietary. It is easy enough to post as you can delete any solutions to reduce size. Screen shots may be helpful but the actual file would be better. Just attach the file. PECs may not always be defined as default boundaries. It depends on the overall geometry.

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