I can't find published power supply rejection ratio data for the VMAG and VPHS outputs of the AD8302, but it seems to be low - I have 100mV p-p ripple at 500kHz on my +5V supply to the AD8302 and it appears with about the same magnitude on the VPHS and VMAG outputs (using the eval board with VMAG connected to MSET anf VPHS connected to VPHS).
(1) Does this sound right? Or could the IC on my board be damaged?
(2) I haven't seen the reason for R4 mentioned in AD literature, but was it included to deal with this problem (i.e. low PSRR + noisy power supply)?