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Standing Waves in Transmission Lines

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If a standing wave pattern is formed in a transmission line is there any transfer of energy taking place between the source and the load???
I know how and why standing waves are formed,but i cant understand the part about energy transfer.
PLEASE EXPLAIN.
 

MikeMl

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Its a matter of degree.

If either the source end or the load end impedance is mismatched to the transmission line impedance, you can wind up with a situation where all the power available from the source is not transferred to the load at the far end. The fact that there are standing waves present is a symptom of the mismatch; not the cause.
 
"A perfectly balanced standing wave transfers energy in both directions at the same time, so there is no net energy transfer"....I dont quite understand what this means.
 

MikeMl

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In any real situation, the mismatch (if any) at the sending end does not match the degree of mismatch at the load end, so there is always net energy transfer. More energy would be transferred if you get rid of the mismatch (at both ends).
 

alphacat

New Member
"A perfectly balanced standing wave transfers energy in both directions at the same time, so there is no net energy transfer"....I dont quite understand what this means.

A wave consists of progressig and retreating waves.
When the amplitude of the retreating wave equals to the amplitude of the progressing wave, this wave (which is the sum of both of them) is called Standing Wave.
The amplitude of the retreating wave could be equal the amplitude of the progressing wave only if no power is delivered to the load.
Therefore, no energy is transferred to the load, meaning there's no net energy transfer as was said in the line you quoted.
 
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alphacat

New Member
Its a matter of degree.

If either the source end or the load end impedance is mismatched to the transmission line impedance, you can wind up with a situation where all the power available from the source is not transferred to the load at the far end. The fact that there are standing waves present is a symptom of the mismatch; not the cause.


I stand by that.
I'd just add that standing waves present is a symptom of a perfect mismatch, where the reflection cofficient's absolute value equals 1.
 

MikeMl

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I stand by that.
I'd just add that standing waves present is a symptom of a perfect mismatch, where the reflection cofficient's absolute value equals 1.
Even with a perfect match at the driven end, and only a slight mismatch at the load end, there will be "standing waves". The reflection coefficient does not need to be unity...
 

alphacat

New Member
Well, I watch online lectures of the course "Microwaves and Transmission Lines" and the lecturer has defined Standing Waves as waves which the amplitudes of the progressing and retreating waves equal to each other.
So was he wrong?
 

MikeMl

Well-Known Member
Most Helpful Member
Read :

Look for this statement amongst the examples:

"In both these circuit examples, an open-circuited line and a short-circuited line, the energy reflection is total: 100% of the incident wave reaching the line's end gets reflected back toward the source. If, however, the transmission line is terminated in some impedance other than an open or a short, the reflections will be less intense, as will be the difference between minimum and maximum values of voltage and current along the line. "

As I said; a matter of degree.
 
For a perfectly lossless transmission line there will be standing waves unless the load impedance is equal to the characteristic impedance of the line,which is purely resistive.In that case a part of the energy is reflected back by the load (not considering OC and SC terminations).Hope I am right.On the other hand for a standing wave to be formed the amplitudes of the incident and reflected waves should be equal.Doesn't this sound like an anomaly???If the total energy is not reflected back,how can the amplitude of the waves be equal???
 
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