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Waveguide amplitude errors, scattering boundary condition

Posted Apr 12, 2013, 12:00 p.m. EDT RF & Microwave Engineering Version 4.2a 5 Replies

Raquel Vaz
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Hello everyone!

I am modeling a waveguide with the purpose of verification, but I am getting high errors in amplitude when the length of the waveguide is not a multiple of the wavelength of the propagating wave (when it's a multiple of the wavelength it converges to analytical solution).

I am using the scattering boundary condition and it should be transparent to the radiation in this case, but it looks like part of the wave is being reflected because the amplitude is bigger than it should be. Anyone had a similar problem or can explain this?

Thank you in advance!
Raquel Vaz

5 Replies Last Post May 25, 2017, 5:38 p.m. EDT
Sergei Yushanov Certified Consultant
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Posted: 1 decade ago Apr 15, 2013, 8:04 a.m. EDT
Raquel,

Scattering boundary condition is not designed for absorbing guided wave. Use port boundary condition or PML to avoid back-reflection of the guided wave.

Regards,
Sergei
Raquel, Scattering boundary condition is not designed for absorbing guided wave. Use port boundary condition or PML to avoid back-reflection of the guided wave. Regards, Sergei
Raquel Vaz
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Posted: 1 decade ago Apr 22, 2013, 8:45 a.m. EDT
Sergei,

thank you for your answer, but I still have a problem and if you could help me with it I would be very thankful to you.

The problem is that I need to do a time domain verification and PMLs and the port boundary condition are not available with the TRANSIENT electromagnetic waves interface. I only can use this alternatives with the electromagnetic waves interface that only supports frequency domain studies.

Best regards,
Raquel Vaz
Sergei, thank you for your answer, but I still have a problem and if you could help me with it I would be very thankful to you. The problem is that I need to do a time domain verification and PMLs and the port boundary condition are not available with the TRANSIENT electromagnetic waves interface. I only can use this alternatives with the electromagnetic waves interface that only supports frequency domain studies. Best regards, Raquel Vaz
Abutaleb Haidary
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Posted: 1 decade ago May 26, 2013, 2:20 a.m. EDT
Hi,
I am doing the same modeling (3D waveguide in time domain) and I have the same problem.
Please let me know if you have solved this problem.
I highly appreciate,

Best,
A.Haidary
Hi, I am doing the same modeling (3D waveguide in time domain) and I have the same problem. Please let me know if you have solved this problem. I highly appreciate, Best, A.Haidary
Raquel Vaz
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Posted: 1 decade ago May 26, 2013, 9:35 a.m. EDT
Hi,

Unfortunately I haven't solved the problem. That I know the only available absorbing condition for transient problems is scattering boundary condition. In COMSOL's help says it's a first order condition and maybe that's why it has such a poor performance. The only conclusion I reached is if the waveguide depth is a multiple of the wavelength of the propagating wave the solution is correct (even with few points per wavelength), if not, there is reflection of the propagating wave that can go as high as 40% of the original wave amplitude (no matter how many points per wavelength).

If meanwhile you discover a solution I would be very thankful if you shared it with me.

Good luck and best regards,
Raquel Vaz
Hi, Unfortunately I haven't solved the problem. That I know the only available absorbing condition for transient problems is scattering boundary condition. In COMSOL's help says it's a first order condition and maybe that's why it has such a poor performance. The only conclusion I reached is if the waveguide depth is a multiple of the wavelength of the propagating wave the solution is correct (even with few points per wavelength), if not, there is reflection of the propagating wave that can go as high as 40% of the original wave amplitude (no matter how many points per wavelength). If meanwhile you discover a solution I would be very thankful if you shared it with me. Good luck and best regards, Raquel Vaz
Rishad Arfin
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Posted: 8 years ago May 25, 2017, 5:38 p.m. EDT
Hello Raquel,

How did you solve the problem? I have the exact same problem ? Any suggestion kindly please !

-Rishad
Hello Raquel, How did you solve the problem? I have the exact same problem ? Any suggestion kindly please ! -Rishad

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