why power adde efficiency of rf power amplifier decreases when the output power rises

in the design of rf power amplifier,power added efficiency is directly proportional to the ouput power then why power added efficiency decreases when increase in out power magnitude?

Because with PAE not only the ouput power is considered but also the input power. It means, if you have a quite low gain amplifier, the amplifier is not "producing" the output power. Most of it comes from the input power and PAE drops.

PAE=(Pout-Pin)/Pdc=(Pout-Pout/Gain)/Pdc

Regards

Because of compression.You see increment in power but it's not linear proportional function of consumed power because of compression.