Small Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 10
Distraction; Situational Awareness; Human-Machine Interface
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance
ATC Equipment / Nav Facility / Buildings
Aircraft X was cleared to follow another aircraft on the visual approach to SNA.  Aircraft X was descending out of 4000 ft and I was about to switch the aircraft to tower when an aircraft appeared 1 mile away at 3500 in direct conflict with Aircraft X.  I issued a traffic alert and instructed the aircraft to turn left immediately if the traffic was not in sight. The pilot responded that they were turning left. When traffic was clear I recleared Aircraft X for the visual approach.  The aircraft that appeared in front of Aircraft X was actually a VFR aircraft approximately 15 miles north landing at HHR.  STARS or our Fusion radar erroneously displayed an aircraft that was not there in direct conflict with another aircraft.  The SNA downwind has been plagued with these types of events as well as aircraft appearing to jump around by more than a mile in some cases.  These events are occurring during a critical phase of flight and having to issue safety and traffic alerts for aircraft that do not exist is dangerous.There are filters in place to help alleviate these events from happening but it is not enough.  Many incidents like this happen or aircraft jump by a mile on the SNA right downwind without controllers reporting the events because we have become desensitized to such events.  The WAM (Wide Area Multilateration) Service Volume is a ground based system being implemented on the LAX final to solve the same problems we are having on TUSTIN.  I suggest that this system be extended to include the TUSTIN sector.
SCT TRACON Controller reported STARS or Fusion radar erroneously displayed a target which caused a fake conflict with a SNA arrival.