Sorry for the late reply but I meant the rotation not coverage. I Should've been more clear.It's impossible to have 360° coverage with just one radar, no matter how much gymnastics you do with swash plates.
Even if you theoretically traverse your swash plate ±90° then also you'll have just 270° of coverage [2x (45° electronic beem steering + 90° mechanical swash plate traversing)]. And if you mechanically traverse beyond 90° then the fuselage of the fighter itself would start blocking your radar.
But my main point was why would they go for a swivel mechanism rather than a swashplate. What are the upsides ?