How do I find the input Z of a cascaded transmission line?

AI Thread Summary
To find the input impedance of a cascaded transmission line, it is effective to first calculate the input impedance of the segment closest to the load and then use that value as the load for the next segment. Adding characteristic impedances directly is incorrect, as impedance mismatches can lead to reflections when connecting different transmission lines. Solutions will vary based on length and frequency considerations. If matching networks are present between segments, each can be treated independently. The correct approach involves iterative calculations rather than simple addition of impedances.
seang
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Can I first find the input impedance relative to the segment nearest to the load, then use the found input impedance as the load in next iteration? Or can I add the characteristic impedances, since they are sort of in series?
 
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If you just hook different transmission lines together, then the impedance mismatches will cause reflections.
Any solution will be length and frequency dependent.

If you have matching networks between the segments then you can treat each segment independently.
 
seang said:
Can I first find the input impedance relative to the segment nearest to the load, then use the found input impedance as the load in next iteration? Or can I add the characteristic impedances, since they are sort of in series?

Your first solution is correct. You cannot simply add the characteristic impedances.
 

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