MIMO radars:

[donkeykongsfist]

Can somebody explain the advantages of a MIMO (or SIAR) radar over a conventional phased array against stealthy aircraft? All that i have been able to find was that it was better at rejecting Gaussian noise and clutter, was supposedly better in detection performance compared to conventional radars, both for closely-spaced and widely-spaced antennas and can provide both wide range surveillance and target tracking. How can this be achieved and what even is SIAR in particular?

[hornetfinn]

SIAR was first radar system that used some rudimentary MIMO ideas about 30 years ago. It was a French system and actually the acronym was RIAS in French (Radar a Impulsion et Antenne Synthetique) but when translated to English, it becase SIAR (Synthetic Antenna and Impulse Radar).

MIMO can have significantly higher processing gain and signal to noise ratio because it transmits multiple different waveforms. This waveform diversity is basically what makes it better in many parameters than traditional phased array radars. Traditional radars only transmit one waveform at the time which limits the possibilities what signal processing can do as there is less information available. Each waveform has different characteristics and having many of them gives more data from the targets and also noise and clutter. This improves the processing gain and also signal to noise ratio. Of course it also means that signal processing needs to be very powerful and advanced enough to handle all that data. Which is why it takes some time before real MIMO radars become reality.