I'm coming again. A huge effort was made for me to reduce the PFD spur in the new PLLVCO ADF4356. But I don't know how to reduce the harmonic spurs.
When the output comes from the VCO directly (f > 3400MHz) , the harmonic spurs appear such as the picture 1. But when the output comes from the divider (f < 3400MHz), the spurs disappear such an the second picture.
f_refin = 140M, R = 2， PFD frequency is 70MHz. REF SPUR is about -80dBc now.
I trust the new PLLVCO ADF4356 can do much more better than now. Maybe my configuration is not good enough, or...
Looking forward to your reply.