You have to kill wave after wave of helghast soldiers to trigger a way to the upper level. Then you do it again to trigger a cut scene that will lead you to his general area.
After that, you get to go 2 (with Rico, but he's completely useless) on 1 with Radec himself. He doesn't stay cloaked forever. He will reveal himself when he attacks.
Ok good, I'm at the balcony right now. I just need to beat him. So a little while left :P
Hey if you guys would be interested, I made a PS3 Clan back at the Escapist. So you could play with people who aren't super annoying online.
/shameless self promotion
I'd say the default controls for Killzone are kinda dumb, I'm glad they included others or I'd be dying left right and centre :P
I played a couple of games online. I'd be interested in joining the clan. Just to chill out and shoot each other's digital brains out.