Is a RF wideband power amplifier made from a set of narrower band amplifiers or is it just one amplifier that is somehow made to be very wide band? For example, a wideband amplifier that spans all the way from high frequency to ultra high frequency would that have several smaller band amplifiers overlapping or just one single power amplifier that covers the entire range?

 

It is unusual to have an RF power amplifier that covers HF to UHF but for a given band, an amplifier can be made 'broadband' by proper design of feedback or emitter degeneration or a combination of both. The trade off is less gain than possible of a narrow band amplifier. Then, bandpass or low pass filters are attached to the output for the band of interest. These can be switched in to select outputs related to the drive frequency. As a side note, it is generally more difficult to design a broadband amplifier than a narrow amplifier.