Mosfet, Mesfet vs Bipolar transistors in RF circuits

I was wondering in general what types of semiconductors are used in most solid state RF power amplifiers like the ones at cell base stations and elsewhere. Do they use mosfets etc which can only switch a square waveform or are bipolar ones also used that can output sinusoidal outputs that can be directly fed into an antenna? Do mosfet amplifiers have an output filter much like the lower frequency class D audio amplifiers or does the antenna function as a filter at such high RF frequencies? I imagine for example an RF amplifier outputting a QAM modulated wave into an antenna so that the signal at the antenna looks like higher and lower amplitude half periods of a sine, but if the amp works on mosfets, does the signal at the transistor output is the same amplitude but square ? One of the reasons I ask this is because I have had limited experience with RF circuits and I am building a est device where I would want to excite an RF cavity that has no capacitance but only inductance associated with it and I would like to drive it with an RF signal that is sinusoidal so I am wondering do bipolar transistors come with high enough power levels at RF frequencies and aren't they too inefficient due to the sinusoidal operation mode vs the on/off of the mosfets etc? PS. at RF frequencies is there any place where a square wave is used or is it all just sinewaves and modulated sinewaves? I guess one cannot even achieve a square wave radiating from an antenna but how about some special purpose RF circuits?

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