Here's a question: is this Passive Radar similar to the PESA on the new Flankers?
To start there is nothing really stealth or invisible to radar.
This is the basic concept, stealth is only signal managment, it means the fuselage of the stealth fighter sends the radar reflections away from the source.
So by using the right tactics a F-22 appears invisible, becuase it flies in a range where the conventional radar has a very small return.
Passive radars considers any signal form any radiation source will be useful, the reason is simple F-22 like J-20 do reflect radar, what happens is they reflect most of the radar away from the source.
The theory of the Cassidian radar is any wave reflected by an aircraft can be detected, however because passive radars use any wave frequency, they need a computer power that was not available in the first generation radars.
Bi-static radars can detect stealth aircraft simple because the stealth aircraft does not absorb all the radar energy, in fact RAM can not absorb all the energy, some part of the energy is reflected, some is absorbed, so basicly J-20 or F-22 still send a signal that can be detected.
But they need two or more radars positioned in different locations.
The Su-35 PESA radar uses another technic, the PESA send a signal, but a very powerful signal, so a F-15 can be located at 400KM, a stealth fighter in the range of 100Km.
Why electromagnetic waves are absorbed by the atmosphere, so if the F-22 by canting and faceting its surfaces to radar send 90% of the radar to a direction away from the radar, 5% is absorbed and only 5% is deflected back, the range of detection is reduced.
So the theory of the Irbis is use a powerful radar why?
Simply some of the radar will be absorbed by the atmosphere before it reaches the target, the stealth fighter deflectes 90% away from the Irbis, 5% is absorbed by RAM, but that last 5% has so much power density, that will allow the Irbis PESA of the Su-35 to detect the enemy fighter.
To put it in simply ways, you simply use a more powerful lamp in the dark to see further, that is PESA radar or SU-35.
The Bi-static is like the stealth fighter is a mirrow that concentrates the energy in one direction so you position another radar or observer to see the powerful light like the uses of heliography.
And a Pasive radar is basicly an eye, yes our eyes are pasive radars that do not send light but have enough cones to detect different objects with clarity, but our eye had more computer power than old radars, but that is not any more.
