It's amazing that these drones are surviving at medium altitude, loitering for long periods in what should be well defended air space. They certainly don't look stealthy. The troops on the ground have no idea they are being targeted as they gather nice and tight into a group.
A few other countries are now providing fixed wing drones with similar capabilities, as well as some hybrid drones (fixed/rotary wing).
Their small size alone makes them stealthy.
The wings & body are composite, which doesn't reflect radar energy.
The engine is hidden and not exposed.
It can fly as high as 9,000 feet, making them impossible to acquire visually.
They orbit at approx 50mph...doppler radars will not display them.
My guess is the best way to locate them is to triangulate their radio transmissions.