variable gain amplifier
It should include a detector to detect power, then the detector voltage compare to the power setting signal to produce a differential voltage to control the VGA.
There are several ways how to control a RF amplifier gain.
One is to use a variable (controllable) attenuator with a stable-gain amplifier.
Another is to use an integrated VGA like RF2637 from RF MicroDevices. There are now many VGAs from various IC Manufacturers.
Recently, digitally-controlled gain RF amplifiers have been introduced as receivers became fully controlled by a computer or micro-controller.
In RF amplifiers the exactly sinusoidal signal is not too important as each resonant circuit restores the signal shape. Therefore you can achieve a wide range of gain by simply varying transistor bias (if you know what it is).