connect 2 antenna to one reciever

In general, you can't.

You CAN buy a single dual polarized antenna and hook that up.

You can hook two antennas up to a single radio, but they have to be RF isolated, like on opposite sides of a building. You would use something called a "power combiner" or "power splitter".

what about mimo systems , the research right now is working in such implementations

Khouly

Well, the detailed knowledge displayed in the question is astounding! But, I assume this guy has a receiver with an antenna connetor, and wants to hook up 2 antennas. If you say mimo, he is probably going to look for Marcel Marceau.

There may be more than one solution and right choice depends on what you need. You may use duplexers and diplexers, splitters and switches, some more complex multiinput front end devices and so on. What is your application?

You can attach two antennas to a receiver,
Say in application like Radars for distance measurement , you have one transmitting antenna & one receiving antenna.
So called Transceiver I guess.