More a terminology question than anything.
As described in the headline, I want to locate a piece of hardware that can accept arbitrary IP streams (be they MPEG-TS, H264, etc - the exact input format isn't important since re-encoding is easy), and can somehow output those streams over a coaxial cable (RF) in a way that a normal, off-the-shelf TV can tune to those streams in the same way they'd tune to a regular TV channel.
This is not a hardware recommendation question. I just want to know what this class of device is properly called so I can locate it myself.