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winglj
Joined: 21 Feb 2005
Posts: 191
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 08 Dec 2008 20:21 transmission line attenuation |
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Hi, everyone. I have a question about characterize the attenuation of transmission line, such as waveguide or microstrip line.
For example, for the EM theory, the attenuation should be the real part of the complex propagation constant real(γ)=α. And it can be converted to dB by 20*log10(exp(α*z)), where z is the length of transmission line.
However, in the measurement or EM simulation, what it can be got is the S-parameters. So how can I get the attenuation from this data?
For example, I simulate an 1" microstrip line in HFSS. It shows that from the insertion loss is around -3.59 dB at 8GHz, but by using the formula 20*log10(exp(α*z)), the attenuation should be -0.19 dB/in. So which one is correct? Do I need to use advanced calibration to get the real attenuation from the insertion loss?
Thanks.
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Abhishekabs
Joined: 12 Jan 2007
Posts: 727
Helped: 84
Location: India
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09 Dec 2008 7:22 attenuation in transmission lines |
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I guess, you can get real values in HFSS.
when you create graph, check right hand side menu.
select real,imaginary,db etc.
you can get direct values. no need to use formula.
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09 Dec 2008 7:22 Ads |
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parris
Joined: 05 Jul 2005
Posts: 23
Helped: 1
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16 Dec 2008 18:42 attenuation transmission line |
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Dear Abhishekabs
You mean that we just need to get dB(real(S21))???
Cheers
Parris
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Abhishekabs
Joined: 12 Jan 2007
Posts: 727
Helped: 84
Location: India
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17 Dec 2008 4:57 s-parameter attenuation |
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see the image.
In this image you will find on right side there are many options such as re,img, dB etc.
According to my info yes you can get real(S21) values.
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