Probably a radar system thst works with the s300/s400 systems. It would only make sense it was that level of radar system that we’d care that much about.
Since the 300—500 Russian systems use multiple radars working together, it would make little sense to have just one component of a very complex system. My guess is that it is a complete system with missiles - probably the latest 400 variant complete - gotten on the Russian military black-market.