Can you use a RCA to Coax adapter to connect an antenna signal to a RCA port on a tv?

Unfortunately that would not what the adapter is designed for. The adapter will only change the connector type, it will not convert the signal from Coaxial to a compatible RCA signal.

Typically when using the Coaxial connection on a TV, you are using it to connect an antenna or cable source which would require the use of the TV's internal Tuner. If you were to try and use the RCA port on the TV, the signal would not pass through into the internal Tuner, which would not allow the signal to be decoded properly. Without the use of the tuner, the Coaxial signal cannot be displayed properly on the TV.