There is a lot of aluminum in a 777, I think it would be easily tracked by radar. Consider that they are tasked with detecting much smaller fighters. If I may reveal classified info from the cold war, my radar had a 240 nm range and I could see targets at max range, coming from Oregon headed for SFO. Big fat arcs. This modern radar is surely much better. A big reflective target up high, out of ground clutter is easy to track. If you search google images for "military radar plot from pulau perak" you'll see a cell phone photo of a graphic shown to the Chinese relatives of the missing. It shows a gap in the middle of the 200 nm track of MH370. I think the only explanation for that is MH370 flew low enough to drop below the radar horizon, then climbed and reappeared.