According to Breatheheavy.com, there is a rumour floating around that Radar is the fourth single to be taken from Britney's latest smash Circus. It seems a bit odd seeing as it is actually Blackout track, but it think it would be a fantastic chance to get this song heard by the general public, especially as it was supposed to be the fourth single off Blackout. The song never saw the light of day as a single due to Brit's personal circumstances, but apparantly Brit's label, Jive, had a contract with the producers of Radar (Bloodshy and Avant) to release it as a single.
As amazing a song it is (10/10), I think it would tank on the charts. Surely every fan now has this song twice anyway! Fan favourites's Kill The Lights or Unusual You would be better choices.