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it is a group of anntennas .
primary intention is to form high directivity or to achieve unidirectional casting
based on phase relations, they are classified into two types i)endfire ii)broadside arrays
A linear array of antenna elements which are spaced by lamda/2 apart and driven with alternating phases has its principle radiation maximum along and , since the field amplitudes now add in phase in the plane of the array.
Such a system is called an end-fire array.here,maximum radiation will be along the line of axis
same antenna with same phase means it will be called as broadside arrays.here,maximum radiation will be perpenicular to the line of axis.
thus,by means of phase relations we can change directionality of the radiation
NOTE:Therefore it is possible to continuously steer the main beam in any direction by varying the progressive phase β between the elements. This type of array where the main beam is steered to the desired direction is referred to as a phased array or a phase-scanned array
note:
i)When an antenna array has elements arranged in a straight line it is known as a linear array
ii)A uniform array consists of equispaced elements, which are fed with current of equal magnitude (i.e. with uniform weighting) and can have progressive phase-shift along the array
I want to add a small comment about "electronics_kumar" note
'NOTE:Therefore it is possible to continuously steer the main beam in any direction by varying the progressive phase β between the elements. This type of array where the main beam is steered to the desired direction is referred to as a phased array or a phase-scanned array'
This type of arrays is called smart arrays (smart antenna) it is an interisting kind of antenna arrays ,and it supposed to used is the 4th generation in mobile communication.
In conventional antenna arrays, there are three main kinds of arrays, end-fire, broadside, and phase-scanning based. It could be further classificed into: linear and non-linear, and uniform and non-uniform.
The main drawback of endfire arrays or broadside is that they're fixed to specific tranmission/reception angle of 0 or 90. There're, however, sometimes applications where we need an arbitrary angle, say 30. Here comes the role of phase scanning array.
However, what I do need to comment about is that there's a big misconception when we talk about Smart Antennas.
In Smart Antennas, the main objective is not that easy of that of the phase scanning, it rather monitors (stastically) the wanted signal and the infereing signal(s), so that the array can reject the interefering and keep the wanted signals with enhanced power (higher SNR). Thus, we could achieve higher capacities and extended coverage, with enhanced QoS. Smart Antennas have gained much attention in military applications since mid 80's in radar systems. However, for mobile communications applications, THEY'RE USED IN THE 3G which already adopted in Korea, Japan and throughout Europe. FOR 4G MOBILE COMM., Multiple-Input Multiple-Output (MIMO) is used which increases capacity and coverage more than that of "conventional" Smart Antennas. MIMO can be thought of as smart antenna in both the transmit and receive sides.
For any Q's about MIMO, you know where to find me. Hope I could help.
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