Well Sferrin's point is that.
In order to control the UAV the aircraft has to emit. Datalink or communication has two kinds of antenna, a blade with wide beamwidth and a pencil beam highly directional antenna.
The wide beamwidth antenna may betray stealth as it radiates in practically all direction with equal strength (aka omnidirectional or -almost- omnidirectional). The pencil beamwidth one often works in high frequency have smaller and highly directional beam which can be steered electronically like phased array. The latter is preferred method as not only highly directional with controlled sidelobes which makes ESM life hard, higher signal strength and therefore bandwidth can be gained.
This highly directional communication beam can be generated from dedicated datalink antenna like MADL or be part of the radar's operating modes.
I would assume J-20 radar will include such mode. This allows transmission and reception of good quality high bandwidth signal from long range.