I have a PCB designed and using the ADF4351 LO. We are interested in broadband operation and have discoverd that output is unstable at bandedges. Spcefically near the top @4400 Mhz or any sub-octave that pushs fundamental to that frequency , VCO is just under 4400 when output desired is just below 2200, 1100, 550, etc. Once below the top of VCO range output is stable. Any suggestions? We are using loop filter values and circuit as used in ADI demo-brd.