SCT controller voiced concern regarding the current waiver requirement for HHR approach procedures and the limited RADAR coverage in the subject area; either RADAR coverage should be improved and/or waiver requirements changed.

Narrative

Aircraft X was on the localizer approach to HHR. The waiver requires RADAR coverage to be adequate; which it was not. The aircraft's target disappeared outside of DEMON; the FAF; for one or two sweeps; and then I lost all RADAR coverage on about a 2 mile final. I am unable to separate an LA arrival from that HHR arrival by terms of the waiver SCT LA area has; if I do not have adequate RADAR coverage. This has been brought up countless times in the past. The controllers have been informed that maintenance says the RADAR is operating within tolerance. However; we routinely lose RADAR coverage between 2 and 1 mile final on the HHR arrivals. The usual course of action is to verify with HHR that the aircraft is in sight or has landed. Recommendation; change the waiver to allow for this known RADAR inadequacy; fix the RADAR system or cancel the waiver. When the HHR approach occurs; you do not know when you will lose RADAR coverage; only that it will probably happen. Consequently; the controller cannot take action until it is too late. Additionally; if an HHR aircraft were to stray north of its final; bear in mind that in my many years at LA; this has never happened; the controller could not tell due to lack of RADAR coverage.