ADF5901 VCO fundamental frequency

No reply after a week implies that either AD don't know (unlikely) or don't wish to tell me.

The logical conclusion therefore is this is a 12GHz VCO core.

Apologies for the delay in response.  I'll get the responsible engineer to respond.

After looking at the datasheet, the divided down AUX/AUXB output frequency range would imply the core is 24 GHz.  See the "AUX PIN OUTPUT" section in the Specifications Table. 

24GHz / 2 = 12 GHz & 24 GHz / 4 = 6 GHz

Also, the first page of the datasheet indicates a 24 GHz core. 

Hi , yes, the fundamental frequency is specified from 24Ghz to 24.25Ghz, there is an aux o/p that can be div / 2 or div/ 4 ( div /2 twice ) regards Brigid.