Wikipedia defines smart antennas as follows
Smart antennas (also known as adaptive array antennas, multiple
antennas and, recently, MIMO) are antenna arrays with smart signal
processing algorithms used to identify spatial signal signature such
as the direction of arrival (DOA) of the signal, and use it to
calculate beamforming vectors, to track and locate the antenna beam on
the mobile/target.
And phased arrays as follows
In antenna theory, a phased array is an array of antennas in which the
relative phases of the respective signals feeding the antennas are set
in such a way that the effective radiation pattern of the array is
reinforced in a desired direction and suppressed in undesired
directions.
From these definitions it seems that two terms define similar things. And yet the article on smart antennas do not reference (in the text) phased arrays and vice versa. To contribute to my confusion, there is a book Adaptive Antennas and Phased Arrays
for Radar and Communications by Alan J. Fenn, which has two major parts: one on adaptive antennas and one on phased arrays. These parts address different problems: smart antennas for nulling out interference sources and phased arrays to scan an antenna field of view. And again the core structure looks the same to me.
So what exactly is the difference between smart antennas and phased arrays?
Best Answer
Simply put: both are different ways of harnessing the properties of using multiple antennas.
In a Phase array the antennas are usually placed in a repetitive pattern like a matrix or circles or hexagons. Often the distance between the antennas is always the same. Phased arrays are used to make these many antennas behave as one antenna with certain properties like a more narrow beam pattern (where the antenna is sensitive and/or emits more power).
I find smart antennas a misnomer as the antennas are not smart at all, the "smart" bit is in the signals which are used with the antennas. This can be used for improving reception by beam-forming or the reverse: enhanced sensitivity in a certain direction.
This "smart antenna" signal processing is also used with Phased Arrays.
You could say that some smart Antenna systems are a simple form of Phased Array. Where a simple Phased array might use 9 antennas, a smart antenna system might use 3 antennas.
You could call any Phased array with signal processing a Smart Antenna system but I would not call any smart Antenna system a phase array. for example some laptops have 2 or 3 Wifi antennas for beamforming and Mimo. You would not call that a phase array but I think it would be OK to call that a smart antenna system.