An RF amplifier is similar in concept to an audio amplifier but built with components suitable for RF frequencies. Because of the higher frequencies involved, the impedance levels of RF amplifiers are generally much lower than for audio amplifiers in order to avoid the effects of parasitic capacitors and inductors.
Often 50 ohms is chosen as a common impedance level. Thus RF amplifiers are usually specified as providing a given output power level into 50 ohms. RF antennas are designed to present a 50 ohm load at their input over their operating frequency band.
When you say "same antenna", I assume you mean the use of one antenna for receiving and transmitting. This is usually the case in mobile transmitters and requires some form of transmit/receive switching so that the transmitter signal does not get into the receiver.
Power is not a concern when the antenna is used for reception but it is important for transmission. The conductors used in the antenna must be sized to handle the transmitter power just like the conductors in an audio speaker must be sized to handle the output of an audio power amplifier. Because of the skin effect, in which high frequency currents tend to flow towards the outside of a conductor, high power antennas can be made out of tubing rather than solid material.