short answer:
LNA = low noise amplifier.
Usually followed immediately by a "down converter".
Found in really old C-band systems.
Today, we use LNB = low noise block-converter front ends which have the amp and downconverter all in one.
An LNB would bolt onto your existing old feedhorn.
Little more modern and less expensive are LNBF
That's an integrated LNB and Feedhorn. (some with two outputs for two receivers)
Modern LNB and LNBFs have lower noise and probably higher gain, along with better stability and phase noise.
These would be needed for the more sophisticated digital transmissions, such as DVB S2.