- Is ADS-B or MLAT RADAR?
It depends on context, unfortunately. For the purposes of your questions below, the answer is “yes”, as technically wrong as that may be.
- When ATC identify aircraft by using ADS-B only, Does controller can say 'Radar contact'?
In the US, yes, because that’s currently the only approved phraseology for controllers to use, even if the contact is not actually from radar.
The ICAO equivalent is “identified”, and the FAA has been gradually coming into compliance with ICAO phraseology, so it’s possible that this will change in the future.
Also, the FAA’s Fusion software takes data feeds from many sources (PSR, SSR, ADS-B, MLAT, etc.) and combines them all into a single display, so the controller may not be aware of which source(s) is(are) providing the target on their screen; all contacts appear to be “radar” contacts.
- Can SSR indicate the aircraft position?
Yes. SSR works similarly to primary radar, with a beam sweeping the sky; the two are often combined into a single unit. However, rather than looking for a reflection from the aircraft’s skin, SSR looks for a reply from the aircraft’s transponder. Either way, the azimuth and range of the reply is then translated to a lat/long position.