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# Transmission line impedance mismatch

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#### yashiro32

##### Member level 1
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 ?

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

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

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

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

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.

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

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.

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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