need clarification about matching

hi every one,please clarify me.
how 50 ohm transmission line is matched to free space while transmitting the power at antenna.
both the impedances are different..
regards
ram

This is why antennas are used. You can look at an antenna as an impedance-matching device between the transmission line and a free space.
For example, a horn antenna transforms the waveguide impedance, ~ 400 Ohms, to 377 Ohms of the free space. A 50-Ohm line must be transformed to TE10 mode by a coaxial/waveguide transition.

In narrow-band cases, the 50-Ohm line can be connected to a dipole through a matching network, again adjusted for an optimum transmission.

Think of free space as an infinitely long transmission line of characteristic impedance 377 Ohms. The specific physical construction of an antenna in free space results in a specific terminal impedance. When your generator or receiver is conjugately matched to that terminal impedance, maximum power is transmitted. The antenna is embedded in free space and, assuming that it is constructed with good conductors and High 'Q' components, it is inherently matched to free space as a transducer of conducted to radiated energy.