Am going to clarify that...
These are the main target resolutions...
- Altitude
- Airspeed
- Heading
- Range
- Aspect angle
The foundation of those resolutions is the pulse. To generate a pulse, you apply power then you cut off power. Like this...
Each pulse have a leading edge (LE) and a trailing edge (TE). Each pulse that reflects off a body produces a return pulse which also have an LE and a TE. The radar then uses the LEs and TEs to calculate the above five target resolutions.
If you send out 100 pulses and you receive 75 return pulses, some consecutively and some scattered, you would still have a target as defined by the radar.
But what the 'stealth' aircraft does is instead of giving you 75 pulses, you get something like 5 return pulses and not consecutive. In other words, because those five pulses are scattered throughout the pulse train, the radar will classify those five pulses as background noise.
Is there such a thing as a 'pulse train' or is it a made up phrase?
https://dspace.mit.edu/handle/1721.1/41030
In this study a linear frequency modulated chirp signal is approximated using two stepped-frequency pulse train waveforms, a continuous wave pulse train and a linear frequency modulated pulse train.
A pulse train can contain one pulse or one million pulses, depending on the system's sophistication. But there is a negative side to having one million pulses in a single burst. Each pulse can be seen as a packet of energy because of the LE and TE. Energy on/off. The shorter the pulse, the less energy. The lower the energy, the lower the distance the pulse can travel without signal loss.
So when you get less than %.001 of your pulse train, the target is essentially 'invisible'. Not because the 'stealth' aircraft does not reflects but because the reflections are extremely sporadic and scattered.
As the 'stealth' aircraft gets closer and closer, more and more packets of energy hits the 'stealth' aircraft and the reflected pulses would begin to cluster, in other words, more and more reflected pulses would appear consecutively. A sequence of anything is a pattern and in radar detection, patterns are good. For the 'stealth' aircraft, patterns are not good.
So when we see claims like these in the public domain, those who understand radar detection principles, design, and operations, usually roll their eyes. Like this --