What is the effect of power match on S11 and S22 in a PA

Hi, by using conjugate matching it is possible to achieve maximum power transfer and also the good input and output matching. But in case of PA, sometimes we are delibarately creating mismatch. How does this effect the S11 and S22, and what kind of measures should be considered to get a good matching while getting a power matching condition also.

One way,I think, is that the output impedance of the active device and required optimum load should be as close as possible, so that that mismatch can be reduced, correct? any other?

circuitslave said:

by using conjugate matching
it is possible to achieve maximum power transfer
and also the good input and output matching.

Click to expand...

What do you want to mean by "good" ?

circuitslave said:

But in case of PA, sometimes we are delibarately creating mismatch.

Click to expand...

What do you want to mean ?

circuitslave said:

How does this effect the S11 and S22,
and what kind of measures should be considered to get a good matching
while getting a power matching condition also.

Click to expand...

What do you want to mean by "good" ?

circuitslave said:

the output impedance of the active device and required optimum load should be as close as possible, so that that mismatch can be reduced, correct?

Click to expand...

Wrong.

Can you understand operation class of PA ?
There are many operation class for PA, class-A, class-C, class-D, class-E, classs-F, class-S, etc.

Even if your PA is class-A, best low distortion is achieved at mismatch condition.
If your PA is for modulated signal, impedance issue will be more complex.

Surely learn very basic things before EDA Tool Play.

S-parameter works fine only for small signal. For PA, s-parameters vary with power level, so X-parameters are used instead. For PA design, efficiency and distortion are more important factors than S11 and S22. Load-pull method is used for PA impedance matching. If you really care about reflection, 90 degrees hybrid combiner could be used to reduce reflection at both input and output ports.

Whether to use conjugate match or power match at the output
Please refer to the figure below

*Lets ignore the reactive part for now
One can immediately see the problem if the output is conjugately
matched. As seen in figure above, for a gain match, the output current swing is quite
small and therefore the available power will be quiet small. On the other hand, if the
real part of the load line is selected as shown by the green line in figure, a larger
output current swing is available, and therefore a larger power output is available.
This is referred to as power matching
What type of matching to do at the input
Conjugate match.
I typically run a large signal s-parameter simulation and find the input impedance at the power level where I am most concerned about. I design my input matching to match at that point.
.

circuitking said:

Hi, by using conjugate matching it is possible to achieve maximum power transfer and also the good input and output matching. But in case of PA, sometimes we are delibarately creating mismatch. How does this effect the S11 and S22, and what kind of measures should be considered to get a good matching while getting a power matching condition also.

One way,I think, is that the output impedance of the active device and required optimum load should be as close as possible, so that that mismatch can be reduced, correct? any other?

Click to expand...

I found this in book Wireless Communications Circuits and Systems, By Institution of Electrical Engineers