Removing the smallest supply decoupling capacitors in multilayer boards
Answer: ADF5901 = 3 sets of 3 capacitors.

From ADF5901 data sheet:


  [Pin No] 4, 5 [Mnemonic] TX_AHI [Description] Voltage Supply for the Tx Section. Connect decoupling capacitors (0.1 μF, 1 nF, and 10 pF) to the ground plane as close as possible to this pin. TX_AHI must be the same value as AHI.


The datasheet repeats this 4 separate times.

But the eval board shows three sets of capacitors adjacent to the ADF5901 for TX_AHI, AHI and VCO_AHI.  RF_AHI and DVDD appear to be connected to AHI.



And three sets of capacitors adjacent to the ADF4159 for AVDD, DVDD and VP.  These pins do not go to the ADF5901.



The designers recommend these capacitors.  It is better to have them and not use them rather than need them and not have them.  I'd follow layout used on eval board.  You know it works.  

There is a second evaluation board and the same capacitor distribution is used.