High Power Amplifier design? Need Help

[has_ajam]

Hi,
I want to design an X band 12 Watt Power Amplifier with a chip HEMT.
I have designed low power Amplifiers befor. an I am familiar with packaged Transistor matching and biasing.
But what points are critical for High power Amps. (X band 12 Watt Power Amplifier)
Have any body any points , papers, good book or ...
They could not be similar to low power Amps? could they
especialiy with chips, what should I do?

 

[memarian]

Dear,

It's similar to low power design ,but depend on your design.In Low Power design

Amplifiers usually work in CLASS-A.When going to medium power and high power

They usually work in Class-AB & Class-C (Class-D,...). In low power you use

S-Parameters for matching design but in medium&high power you usually have only

Zin & Zout (or Zin & Zl) of the transistor (Optimum Input Impedance,Optimum Output Impedance ...)

and you must design matching circuit to convert 50 ohms to the Conjugate of Zl or Zin.

Finally Take a Look @:

**broken link removed**

They have internally matched power GaAs FETs (Matched to 50ohms).

Good Luck!

 

[rf100]

search for books by crips
they are very good and they are in the forum
good luck

 

[Darren_pan]

I'm confused,as you said,the S parameter is used for lower power..but we know the S parameter is suitable for high frequency. so ,if one day ,you wanna design PA, work in high frequency with high power. which parameter could we choose?

 

[MoonShine]

For large signal design, s-parameters are no longer applicable. One must use large signa impedances. Z-parameters are often provided over a frequency range that the device is intended to operate. S-parameters are only suitable for linear excursions from the bias point, large signal implies non-linear excursions from the bias point or the non RF point. As mentioned, Cripps deals with this aspect quite well.

MoonShine

 

[has_ajam]

how can I find the crips books