The problem to inject a signal into an antenna comes up from the fact that antennas have tipically a low impedance (50 Ohm). So you'll need a circuit that is able to feed a proper POWER into antenna. The covered range depends not only on transmitted power but also on receiver sensitivity (minimum detectable signal).
Usually transmitters have power from -10 dBm to +20 dBm (it is a large range...).
So your problem can be solved like this:
-given 10m distance, calculate path loss at your working freq and add some margin (for example 30 dB loss +10 dB margin).
-given your receiver sensitivity (for example -60 dBm), calculate trasmit power at antenna (-60+40=-20 dBm)
-given antenna gain (for example 5 dBi), your power amplifier have to feed into antenna impedance -15 dBm.
I have done a very quick exercise, but I hope I've been clear enough to give you some guide line.
Mazz