MIMO = Multiple Input Multiple output
In MIMO structure you have multiple radars (take for example 4 radars) spread in an area. All 4 radars location is known by the other radars and all of them transmit in a different frequency (so each radar signature is different) and all of these radars can receive these 4 different frequencies and calculate in their software what the distance and speed of the detected target that is flying over this area.
Even if the target is stealth and bounces the radar signal into a different direction the other radars can pick up the signal of the first radar. Due to MIMO technique the stealth feature of a "diamond" like shaped stealth object to bounce the radar signal to a different direction to avoid detection is compromised and stealth aircraft is no longer "stealth".
downside of this technique is that the target has to fly over the area with these MIMO radars so the cross detection can work. It works a bit like triangulation.
FMCW stands for Frequency Modulated Continuous Wave radar and is more like the MMW radar you'd see on helicopters, range is not so superb but has high resolution
I know what mimo radar is, and thanks for the explanations.
FCMW has been developed in 2000s and in use since 2010 in 2 marine radars i know, so it is not something relatively new for Tübitak or Aselsan thus i didn't assume they would keep it secret unless it was something new. But M5 is telling otherwise, they i might be wrong. MIMO won't be ready soon as the Gözcü radar they have claimed soon to be tested.
Also about MIMO:
MIMO radars use modulation as well, each transmitter modulates a unique arbitrary waveform just the way it is done in FCMW, so that the receivers can distinguish the source transmitter and later process the data to merge into a single image.
MIMO radars come in two different configuration, mono-static and multi-static, and the target doesn't actually need to pass from the domain, a full radar image (360 degrees) can be created only when it is passing through the domain as you have explained, unless otherwise, it still improves spatial resolution because it may catch scatters from different angles. I don't know much information regarding to the mono-static MIMO radars but it is relatively new subject as well and told to improve spatial resolution which i think matters for detection of stealth aircrafts.
I don't know a lot about radars but using my knowledge on bi-static and multi-static sonars,i am trying to interpret as much as i can. In sonars the target doesn't have to pass through the domain yet bi-static or multi-static sonars still detects threat in greater ranges than SISO, and can create a better estimation of the target's shape, main dimensions.
I have re-read the M5 and found out some parts of the radar was already manufactured, so it is something to be tested soon, MIMO will be done beyond 2023.
Further edit:
Just figured out FMCW modulates the signal in a single pulse, while modern AESA radars (or rather any radar with digital modulation) are able to change frequency at each pulse. The latter also have similar LPI capabilities of a FMCW based LPI radar.