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Transmission line impedance mismatch

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yashiro32

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If a mismatch of impedance is due to the transmission line not due to the load, can i conjugately matched the input impedance to the mismatched transmission line impedance ?
 

vfone

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Yes, you can.
Measure first the input impedance of the mismatched TL, and after that match it to 50 ohms (or whatever you want).
 

yashiro32

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My transmission line is a microstrip line , how do i measure the impedance of a microstrip line ?
 

vfone

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Just measure the impedance at the input of the mismatched TL (using the Network Analyzer) and match that point to whatever impedance you want.
 

bingjiang99

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let's forget the impedance mismatch. How can we know the impedance and electric length of the microstrip transmission line?
 

balaguru thavamani

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Impedance(Z) of the microstrip transmission line depends upon the width of the strip(w) and height or thickness of the substrate(h). And the expression is,
For w/h ≤ 1,
Z=(60/√εeff)*{ln[(8h/w)+(w/4h)]}
For w/h ≥ 1,
Z=120Π/√εeff{w/h+1.393+0.667ln[(h/w)+1.444]}

Electrical length depends upon your frequency.
 

yashiro32

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Back to the impedance mismatch, what kind of circuit should i used to matched
the impedance, etc, Tee or Pi network?
 

bingjiang99

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balaguru thavamani,
thanks. I know these equations. However, I want to know how I can get the impedance and length values by using VNA.

balaguru thavamani said:
Impedance(Z) of the microstrip transmission line depends upon the width of the strip(w) and height or thickness of the substrate(h). And the expression is,
For w/h ≤ 1,
Z=(60/√εeff)*{ln[(8h/w)+(w/4h)]}
For w/h ≥ 1,
Z=120Π/√εeff{w/h+1.393+0.667ln[(h/w)+1.444]}

Electrical length depends upon your frequency.
Added after 1 minutes:

imodelit_moderator

Thank you very much for this link.


imodelit_moderator said:
Dear bingjiang99,

Check this applet: http://imodelit.com/ViewDetails.aspx?AID=142. Thanks.

Best Regards,
imodelit Moderator
 

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