As mentioned - a duplexer with a single antenna is the 'gold standard" for most repeaters.
The idea is to keep the transmitter output (only 600 KHz away from Receiver input frequency) from Desensing (overloading) the receiver making it short-range and of little use.
Two antennas, widely separated, and with minimum coupling between the cables and Repeater equipment in the shack will also work but a bit touchy to effectively max out the separations to prevent desensing..
IMPORTANT: You must coordinate the Frequencies you are going to use with the local or state Repeater Coordination Council before firing up a system that COULD mess up other systems!!
Also: you must have (or be) a monitoring control Operator 24/7/365..
Good luck and enjoy - Tom, W4NOV
Sorry - a few words didn't hack it.