RW20
I'm with you on the RNAV/ GNSS approaches. The subject of one of my previous rants, asking why in this century SOU does not have them - ask Shoreham's users what they use, an NDB or GNSS approach!
As for the radar, SOU has a dual system, primary radar (ie a system which detects aircraft using reflected radar pulses) and a Secondary Surveillance Radar (SSR) which uses data from an aircraft's transponder (ie the squawk).
In the event of a failure or temporary withdrawal of one system (eg for maintenance), the other can be used, albeit with limitations. Haven't see the current NOTAM, which may specify an unserviceability or maintenance withdrawal.