how good should be power supply ripple for a VCO to operate properly


I am doing research on wireless recievers. I am using a VCO from Hittite to provide LO. I have supplied power to VCO from a Rhode & Schwarz regulated power supply unit. I did not see the expected performance of VCO. Lot of phase of noise was present. We are planning to buy a SMU. I want to know how good should be the ripple from power supply unit for better performance of very sensitive RF components like VCO. I would use this info during purchase of SMU.

Kindly let me know !