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Load pull values as frequency increases

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circuitking

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Zopt by Load pull as frequency increases

Hi Is there any procedure to theoretically/analytically find out how the optimum impedance values obtained by load-pull change as the frequency increases? I have seen in most cases impedance moves on the smith chart in anti-clock wise direction as the frequency increases. Is this true in every case ans why?. Thanks
 

BigBoss

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I think you misunderstand the concept of Load Pull..
Load Pull measurements/simulations are done for one frequency only at a time so there is no increments or decrements by frequency.
There are some contours on Smith Chart that represents optimum <load/source impedance/PAE/Delivered Output Power> single point and regions around it ( by paying off the optimum performance )
If you change the frequency simultaneously, you'll probably get a path that draws a curve associated Optimum Points for each frequency on Smith Chart.
 

circuitking

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Re: Zopt path bz Load pull as frequency increases

If you change the frequency simultaneously, you'll probably get a path that draws a curve associated Optimum Points for each frequency on Smith Chart.

Yes, I am asking about this scenario. How do I know what should be this path?
 

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Re: Zopt path bz Load pull as frequency increases

Yes, I am asking about this scenario. How do I know what should be this path?
There isn't any method to predict this.Either you measure ( best method ) or simulate .An approximate Analytic method is Load Line Theory of Mr. Cripps but it's just rough approximation.
 

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The optimum load impedance curve represents the output impedance of your power stage and depends on it's topology and component parameters, also on the transmission line length between PA and your output reference plane.

There may be a typical behavior of certain PA types, but no general rule.

What's the background of your question? Usually load pull and impedance matching is performed for a single frequency respectively small band. Are you intending wide band matching?
 

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