AFAIK stealth technology depend on 2 factors :
1) Absorbing material
2) Scattering the incoming RW so it won´t bounce back to the incoming direction.
Radar work like a lightray on a mirror, you will only receive any signal back if the lightray hit the mirror in an angle it can be noticed form the emitting point.
But as sayd before complications arise. any object will send RW back, birds , clouds, rain, skydivers. (picture that your skydiving having fun with friend then of nowhere a patriot is lauched at you...)
To avoid lauching SAM at seagulls and unfortunate skydivers, or having a radar flooded by to much info, there´s a fine tunning to be attained.
the obj of stealth tech is to lower quantity of radar waves being send back to receiver position in such a way it will be considered irrelevant by the software analysing received waves.
This coud of course be countered by triangulation having a widespread array of RW receivers so you can filter and pinpoint in a better way. But its awesomely costly.
This was more or less the approach used by Russian earlier when SU and MIG did not have radar emitter the info being provided from a web of ground mobile/static radars.
But this tactic was put in check mate by long range HARM and AAM, that could easely take down airplanes or radar emiters from too far away, eating the array by the borders or even pushing holes in the array with deep strikes leaving airplanes blind and air control with blind spots. This tactic also had another problem, radarless airplaines where unable to enter much ennemy territory.
The new radar Russian had boasted before the Berlin wall fall was an attempt to 3d wave reception of diferent lenght waves.
USA boasted it Failed having made stealth incursion undetected and CCCP never said anything about those declarations, since it would unwise to broadcast failure or success.