The problem (or advantage) with so-called 'fifth generation' fighters is that they are deliberately designed to be discarded in the 'Detection' stage, leaving the radar system with nothing to 'Track'. Any fighter prior to this admitted arbitrary 'fifth generation' classification will have its RCS very trackable.
Can you explain bold part in detail?
Sure...
I already outlined the three stages of radar operations:
- Detection
- Tracking
- Targeting
For your question, I will explain the 'Detection' stage.
If you take an antenna, regardless of shape, you can tune it sensitive enough to pick up even cosmic background radiation (CBR), as well as music radio, or TV. Inside the 'Detection' stage, there is usually a process where we take these known signals and immediately reject them. We call this process 'clutter rejection' and the electronic line is called the 'clutter rejection threshold'. Essentially, what is 'clutter' is just stuff that we do not want to bother displaying.
But there is a catch...
For a meteorologist, a storm formation is desirable for display but an aircraft is not desirable. For the air traffic controller, both are desirable but he will have the aircraft on one display and the nearly storm cloud on another display. For the fighter pilot, sometimes weather phenomena and mountains are desirable, sometimes not. It all depends on the situation. The fighter pilot does not care to see birds, but for the biologist trying to study bird migration for the Agricultural dept birds are very desirable for display. In sum, what is 'clutter' is arbitrary from interest to interest.
Still...There are certain
TYPES of radar echoes and signals that an antenna may pick up that we simply do not want to display. For military aviation, those signals are CBR, assorted civilian communication signals, birds, and many others. These 'junk' signals are grouped into that 'clutter rejection threshold'. What a so-called 'fifth generation' fighter does, or was designed, is to be inserted into that automatic rejected region.
Before the F-117, the most popular method of being inserted into that rejection region is to fly as low as possible so as to blend in with ground return, meaning as the radar looks at the Earth, which is a very large target with many features like mountains, plants, and animals, the radar will be so inundated with echoes that its automatic gain control (AGC) circuits will kick in to reject these signals. The fighter that is flying so low in altitude and among these signals will be discarded by the radar. The tactic works very well but it does have high risks for the fighter, mainly very limited maneuvering room.
The F-117 and later fighters were deliberately designed, or body shaped, to the point where even though they will produce radar echoes, those signals are so small and so briefly detected that such signals, when they are detected, they are immediately discarded when they are held against the table of known signals that the radar system is authorized to dismiss.
So...If you are immediately dismissed how can anyone track you, let alone mark you as a target?
