About the spurious noise on EV-ADF4159EB1Z

Hello,

In EV-ADF4159EB1Z, the following spurious was confirmed. (span is 1MHz)

     

Is this an unavoidable spurious noise?
Or if there is a cause, can we avoid this spurious noise?

The conditions are as follows.

P/N                            : EV-ADF4159EB1Z
Reference frequency : 100MHz
Output frequency      : 12GHz
Register setting         :
 R0   :300F0800
 R1   :00000001
 R2   :0001050A
 R3   :010300C3
 R4-1:00180104
 R4-2:00180144
 R5-1:00000005
 R5-2:00800005
 R6-1:00000006
 R6-2:00800006
 R7   :00000007

Regards,
Tatsu