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Computing S-parameters

Posted 30.08.2022, 16:28 GMT-4 Version 6.0 2 Replies

Manal Shlebik
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Hi everyone,

I would like to compute S-parameters. As it is known that the S11 parameter describes the reflections, and the S21 parameter measures the wave that is transmitted through Port 2 when the waveguide is excited at Port 1.

S11= (Reflected Energy/ Incident wave), and the S11 value should be near zero for the perfect case.

S21= 1 - S11, and the S21 value should be near one.

I have used the S parameters that are available as built-in expressions, ready for evaluation in postprocessing but I got S11= -1.2194E13 and S21= 5.6967E12, which are incorrect values.

I have tried another way which is creating the Global Evaluation node and writing in the Expression section the below equations:

intA(emw.Qrh)/(Port input power) >> for Absorption

(intR(-emw.Poavx))/(Port input power) >> for Reflection

intT(emw.Poavx)/(Port input power) >> for Transmission

(intR(-emw.Poavx)+intA(emw.Qrh)+intT(emw.Poavx))/(Port input power) >> for total (A+R+T)=1

However, I still have the same incorrect results, as shown in the attached COMSOL file

Would you please show me how I can compute the S parameters correctly?

Thanks in advance,Manal

2 Replies Last Post 31.08.2022, 17:58 GMT-4
Dave Greve
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Posted: 2 years ago 31.08.2022, 13:59 GMT-4

The way you try to evaluate something to compare with the S parameters is clearly wrong as |Sii| must be less than or equal to one. I'm not sure why, I wouldn't do it this way.

A plausibility check. Integrate emw.nPoav on input and output ports. I see 82.4 W in (less than 100 because there is some reflection); 38.5 W out, and 41.2 W dissipated in the absorber (volume integral of Qh). So approximately all the power is accounted for. The S values are roughly consistent with these numbers.

The way you try to evaluate something to compare with the S parameters is clearly wrong as |Sii| must be less than or equal to one. I'm not sure why, I wouldn't do it this way. A plausibility check. Integrate emw.nPoav on input and output ports. I see 82.4 W in (less than 100 because there is some reflection); 38.5 W out, and 41.2 W dissipated in the absorber (volume integral of Qh). So approximately all the power is accounted for. The S values are roughly consistent with these numbers.
Manal Shlebik
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Posted: 2 years ago 31.08.2022, 17:58 GMT-4

Dear Dave

WOW, your answer helped me a lot, now I can compute S-Parameters easily,

Your help is really appreciated, thank you so much.

All the best, Manal

Dear Dave WOW, your answer helped me a lot, now I can compute S-Parameters easily, Your help is really appreciated, thank you so much. All the best, Manal

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