Trade-off between linearity and output power in class A amplifier?

[crayon]

Hello everyone,

I am working on a high linearity (~40dBm OIP3) X-band class A PA design. Output power should be in the range of 20~25dBm. The amplifier needs to be matched to 50ohm impedance.

Here is the problem. I used conjugate matching for the amplifier output (it can be treated as unilateral). The output power increased at the designed frequency of the matching section (CPW open stub) but the OIP3 drops almost 10dB at the same time. Since I do not have access to a load-pull system, I just tried several different load impedance values. It appears that load impedance with larger mismatch tends to give a higher OIP3. According to the publications I found, the load impedance that gives highest OIP3 should be very close to that gives largest output power. Any suggestions about this? Thank you.

 

[tony_lth]

The maximum power match point is different from the maximum OIP3 match point and best VSWR match point. At X band,you can try to find some MMIC (internal matched to 50R) power amplifier from Eudyna or Hittite etc. Always the MMIC can reach output power and OIP3 at the same time.
Also you can combine two MMIC amplifier to make OIP3 increase 3dB.