A
smart antenna
is a system composed of a number of independent antenna elements
whose signals are combined so as to favor reception of a
desired signal and reduce interference from undesired
sources.
For a transmitter, the antenna will direct a greater amount
of power toward the intended receiver, wasting less
in undesired directions.
Those funny looking three-sided structures at the tops
of cell phone towers are examples of smart antennas.
They help the base station to focus on the signal from
your phone and ignore the one from the phone in the next block.
Many Wi-Fi systems utilize multiple antennas, partly to
reduce interference, but mostly to reduce the effects of
multipath.
Many other applications utilize
or could benefit from smart antennas.
The US digital television broadcasting standard
(ATSC) is particularly sensitive to multipath,
so many ATSC decoders support the use of electrically
steered external antennas.
The FM broadcast band suffers from position sensitive
signal degradation caused by multipath.
This is particularly
common in mobile installations,
so many high end car radios support
diversity reception,
which chooses the best signal from two physically
separated antennas.