The envelope sampling is the start of the back-end process. Normally
the beamformed signals are converted to real (I) and quadrature(Q)
components. These two components can then be combined to obtain
the envelope of the signal.
This step is followed by amplifiers (TGCs) that can be controlled by the
user to operate linearly at one extreme, or as a logarithmic amplifier at
the other extreme, or between.
For wide-band systems, this approach will introduces a lot of errors
when generate the envelope. New approaches have been developed to
reduce the errors and achieve higher resolutions.