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Why is (b_nXa_n^*b_n^*Xa_n) pure imaginary?

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ruwan2

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Why does the available power equal abs(b)^2-abs(a)^2?

Hi,
I read a S-parameter tutorial. It first has such an equation:

Pav0.PNG

Then, it has another equation:

Pav.PNG


I am puzzled why they are so different?

Can you explain it to me?

Best Regards,
 
Last edited:

Pin is the Power which is entered into circuit.Pavs is Available Power from Source.
They are obviously different.If Pr is zero ( conjugate matching ) all power available from the source enters into circuit.
 

Re: Why does the available power equal abs(b)^2-abs(a)^2?

To start with we should clarify some terminology:
Pavs (aka the available, incident, exchangeable power from the source)=|a|²
Pr (reflected power)=|b|²
Pin (absorbed, transmitted, or actual power) =|a|²-|b|².

So the equation in the first attachment is fine: Pin=Pavs-Pr.

But the second attachment is completely off. I'm not even sure why the condition ΓL=ΓS* is relevant. That doesn't have anything to do with conjugate match condition...

- - - Updated - - -

pancho_hideboo said:
Equations are wrong.
Pavs has to be Pin.
Click to expand...
I'm guessing that here "Pin" doesn't mean "incident" power, but rather power absorbed by the load... I know, very sloppy.
 
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