Thermo
All our safety critical systems have some form of back-up or redundancy - or so we are told! There are normally two radar heads at a radar site, the signal travels via two separate lines to wherever the radar displays are and I'm sure that an engineer will tell you that other safeguards are in place. Doesn't necessarily mean that a certain radar won't fail but it reduces the odds. Also you could say that overlapping radar coverage is some sort of back-up
As for radio transmissions, each frequency is served by two (or three) distinct transmitters and we (at ScACC) have two back-ups that the controller can have immediate access to. One bypasses a lot of the electronics in the building but uses the normal transmitters whilst the other provides a direct telephone link to separate transmitters just in case the usual two have failed.