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On microstrip impedance computation

Posted 23 mag 2013, 10:46 GMT-4 RF & Microwave Engineering Version 4.3a 2 Replies

Filippo Micheletti
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Hi everybody,
I'm a very beginner COMSOL user, I started just some few days ago with the 4.3a version and I need to build some microwave sensor models.
I started trying to realize some very simple simulations and one of these is computing a microstrip line impedance.
I built the geometry of a section of line and enclosed it into a PEC box, so I added materials and 2 lumped ports to the two edges of the line and now my question is: how do I compute the characteristic impedance of the line?
I think the best way would be by substituting one of the port with a PML and so obtaining the characteristic impedance of the line as the remaining port impedance but I didn't succeed... any suggestions?
Thank you in advance!
2 Replies Last Post 24 mag 2013, 10:41 GMT-4
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago 24 mag 2013, 09:47 GMT-4

Filippo,

you could do a parameter study of port impedance and look where S11 is minimum and/or S21 is maximum.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Filippo, you could do a parameter study of port impedance and look where S11 is minimum and/or S21 is maximum. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Filippo Micheletti
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Posted: 1 decade ago 24 mag 2013, 10:41 GMT-4
Thank you for reply, I used a similar way to the one you've proposed: doing a parameter study I looked for two consecutive points where the first port impedance becomes real; in one of these points the line length is lambda/4 + n*lambda/2 and the port impedance is equal to the load one, ZL (that is the other port impedance, 50 Ohm in my case), in the adjacent point instead the line length is n*lambda/2 and the port impedance is Z0^2/ZL (with Z0 line impedance) so you can easy find the value of Z0.
This work well, ok, but I want to understand how to use some fatures of COMSOL like a PML or a similar way to impose an adapted surface... how can I do it?
Thank you for reply, I used a similar way to the one you've proposed: doing a parameter study I looked for two consecutive points where the first port impedance becomes real; in one of these points the line length is lambda/4 + n*lambda/2 and the port impedance is equal to the load one, ZL (that is the other port impedance, 50 Ohm in my case), in the adjacent point instead the line length is n*lambda/2 and the port impedance is Z0^2/ZL (with Z0 line impedance) so you can easy find the value of Z0. This work well, ok, but I want to understand how to use some fatures of COMSOL like a PML or a similar way to impose an adapted surface... how can I do it?

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