Oscillator output power

I have a HEMT oscillator and it is biased at a drain voltage of 1.5V and this DC voltage at drain is converted into AC because of negative resistance at the output.What value of output signal should I expect?Would the output signal be 1.5V peak to peak?There are no losses in between.

1.5V pk/pk on 50 ohms means an output power of about +16dBm.
I don't think you can get such output power from a single stage microwave HEMT oscillator supplied at 1.5V DC. If you get 10dB lower power (+6 dBm) you can say you are lucky.

Oscillators can be considered as mildly driven power amplifiers. The output power can be found under this assumption.