single or transmitting signals. Generally, this can be done by
Multipath rejection - Composite information from the array is
using FIR (Finite Impulse Response) tapped delay line filter.
used to reduce the multipath propagation.
Mainly, these were developed for military communication and
Better coverage - By Changing the direction of the beam, it can
intelligence gathering purposes at the beginning. But the growth
be focused to the desired direction.
of cellular telephone industries has created new opportunities
for the smart antennas. Switched beam antennas and adaptive
The Smart antenna technology has paved the way for the devel-
array antennas are the main types of smart antennas.
opment of other new technologies, especially in wireless communication systems. When we consider the smart antennas in
SWITCHED BEAM ANTENNAS: These have multiple fixed
the mobile wireless applications, it can provide higher system
beams with one beam turned towards the desired signal.
capacities, higher signal to interference ratios, lower power levels by directing narrow beams toward the desired direction, while
ADAPTIVE ARRAY ANTENNAS: The radiation pattern of the
nulling undesired directions. Further, this allows greater frequen-
array is adjusted continually to meet a certain performance cri-
cy reuse within the same cell. Thus, with all the above features,
terion while simultaneously identifying and tracking the signals.
higher data rate can be achieved in the mobile network. In radar
MSE (Minimum Mean Squared error), SNIR (Maximum Signal-
applications, accurate estimation of DOA (Direction of Arrival)
to-Noise and Interference Ratio), ML (Maximum Likelihood) and
and multipath reduction is very important factors for imaging
Maximum gain are the few examples for performance criterions.
objects or tracking moving objects. Therefore, smart antenna
technology is used for those purposes. In this way, there are many
A more complex environment such as interference, number of
applications of smart antenna technology. MIMO (Multiple-Input
users, propagation complexity requires smart antenna concept.
Multiple-Output) systems, tracking systems, aerospace systems,
Also, smart antennas have special features. They are;
underwater applications and radio astronomy are few of them.
Thus, the antenna technology has immensely contributed to the
High gain - multiple antenna elements are used to receive
development of communication industry.
signals. Then, all signals are combined in an optimum way to
achieve high gain.
ISHAN CHANDRASIRI
Department of Electrical and Electronic Engineering
Interference rejection - Using DOA (Direction of Arrival) algo-
(Final year)
rithms, the direction of incoming signals can be identified. So,
interferences can be rejected by changing the radiation pattern
analyzing the direction of the incoming wave.
DIRECTING NARROW BEAMS TOWARD
THE DESIRED DIRECTION WHILE
NULLING UNDESIRED DIRECTIONS.
Source: blog.rogerscorp.com
Gauge Newsletter
University of Peradeniya
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