400mhz pa matching

I have designed a narrowband PA of 380MHz~400MHz/25W using the Transistor MRF15035 from Freescale. But the testing result show that the IMD3 is only -13dBc ,(the tesing condition is : 41dBm each tone and the spacing is 100KHz). So the linearity is too poor to use.

the power supply should be 12.5V , the current should less than 4.4A when output is 25W, the IMD3 should be less than -22dBc@41dBm each tone, and-26dBm@38dBm each tone.

Can anyone provid any information about the RF transistor choosing?

Thank you!

I think you are talking about MRF1535, and not MRF15035 which doesn't exist.

http://www.freescale.com/files/rf_if...5N.pdf?pspll=1

This is a very reliable transistor and for impedance matching just follow the Freescale Application Notes and everything will be fine.

Sorry, That is MRF1535.
Yes, it's reliability is no problem. I mean that the linearity of this LDMOS transistor is so poor that it can't meet the specifications about IMD3. I need a transistor opreating at 12.5V with a little better on performace of linearity.

Units are confusing
Is the second unit is dBm or dBc?
if this is dBc it may be possible if it is dBm then you need to use FFPA to solve this issue.

what I mean is that the IMD3 should be less than -22dBc when the output level of each tone is 41dBm,and less than -26dBc when the output level of each tone is 38dBm.

Did you try to increase a little bit the quiescent current, and to load-pull the output match for best linearity?

Yes, I changed the quiescent current, but the linearity is still not so good.
I'm tunning the output match still today, hope to get some improvement.

Added after 2 minutes:

To vfone:

Are you familiar to the pd55035 from ST? How about it's linearity performance?

No, I never used the ST transistor. Seems that the two transistors characteristics are very similar. Just give a try to ST, and maybe you get more luck.
Load-pull should improve the linearity response.