Stealth works in two ways: absorption and scattering. Absorption works by soaking up some of the RF energy, but is limited. Effectively absorbing the RF is li

Stealth works in two ways: absorption and scattering. Absorption works by soaking up some of the RF energy, but is limited. Effectively absorbing the RF is limited by physics, since you can't put a 20 cm thick coating on a plane and expect it to fly. Scattering works by keeping the RF from being reflected back to the transmitter, which is also the receiver in a monostatic design. If you can stick a receiver into the path of scattered energy, you can theorectically detect it. However, there are some issues to overcome to make a good multistatic system. Scattering disperses the energy, so it's not like the receivers are getting a particularly strong signal, so you need a big high gain antenna. That's easier for the home team playing defense, but kind of hard for an attacker who has to stay portable. Then you also have to overcome the communication issues. Radar requires precise timing, which is easier when the transmitter and receiver are right next to each other. You can send a precision timing signal over large distances (precision timing is one of the reasons that GPS exists, as well as Europe's, China's, and Russia's versions), but you have to actually take the theory of relativity into account when designing the system- clearly not impossible, it just makes the math a smidgen harder. You also have to control the real estate to put multiple antennas out there. You also have to get your receiver into the path of the scattered energy, so you are SOL if your receiver is on the ground and the stealth plane is scattering all the RF upwards (unless you have antennas in space...). Multistatic systems are feasible and operational versions already exist. But there are enough tradeoffs that traditional monostatic systems aren't going anywhere. A good defense would use a bistatic system as one of the many layers of surveillance.