why my PA power increased very quickly?

I have designed a PA,when i increase the input power by 1dB,the outpower increased 1.5dB,i can not explain this result,who can tell me why this occurs and how to improve this!

bad measurements or bias point changing

What do you use to measure ? Power meter or SA ?
If you're using Power Meter, the equipment will measure the total power including harmonic powers.
Therefore if your amplifier goes into saturation, harmonics will be increased quicker than main carrier so power seems to be increased bacause of total power.

thanks for your heip! i measure it with power meter!i think bigboss's explains are true!the pa's 2nd harmonic is so higher.

because of gain expansion? I am not sure.......

patriot
my test result is true and correct!i use the power meter 437B and the source Ｅ４４３２Ｂ!but gain expasion occured,so i can't give an logical explain!

You can measure Pout by SA, to confirm is it because of harmonics or gain expansion, Gain expansion is a nature of PA ( mainly related to bias),

Actually, the active device doesn't have a constant gm, which also changes with bias point. So if you want to get a constant gain, maybe it's better increase a little the bias point.

Please refer to: Cripps, RF Power Amplifiers for Wireless Communications, 2ndED, chapter 3.5 Reduced Conduction Angle Mode Analysis and the figure 3.10.