LMX2595: Usage of multiplier and degradation in phase noise

Tool/software:

Hi 

I am using LMX2595 which takes reference of 70 MHz to generate 12GHz signal . I am using doubler , so in the output, I see spur at the offset of 140 MHz offset .

To compensate, I tried using the internal multiplier to increase the PFD to 280 MHz . But with that , phase noise degraded drastically.I wanted to know , is this expected or multiplier is not recommended.

Regards

Vikas