ADF4371 Phase Noise Concerns very low at 5,25,50KHz offset to carrier 35dBc

Question

1. Since we haven't reached device optimal performance we are working on it from last 6months still we are wondering we are stuck in phase noise problem. It is worse than we expect 35dBc @50KHz 
 
 For optimisation of phase noise in Eval-ADF4371 We have tried lot software changes done so far still we are working on it. 
 From hardware we have tried different types of loop filters and different combination PFD upto 200MHz, 100 MHz by using ADF4351 as well as 10 MHz 50 PPB Stable clock. 
 Power supply chain we have used Rigol smps as well as cosel, traco power modules changed different combinations 
 My working band is x2&X4. i.e 8-30 GHz here out put power level variation also around 7 dbm at x2, 10 dBm @X4 port. But my concern is phase noise 
 Please help me ou from this problem currently we have changed loop filter is 200KHz 
 Response to above loop filters wasn't good its around 35dBc@5,15,25 KHz. Spectral quality is degraded. Spectrum is little bit shaking(like small vibration) Please help me out of this problem we have purchased 1.Eval-ADF4371 board and two ADF4371BCCZ SMD IC from ANALOG DEVICES 
 If you have questions about how good my PFD, DC source and loop filters we have used same configurations for EV-ADF5355 this board phase noise as well as spectrum quality is very good as compared to EV-ADF4371.

ADIApproved · Accepted Answer

Phase noise at 5 kHz, 10 kHz and 25 kHz highly dominated by the reference noise, so you need to select the reference source carefully.