Phased arrays are not restricted to radar. Sonar sometimes also
employs the technique. The array consists of multiple elements
(aerials or transducers) which are each fed by signals which are
delayed slightly from each other, ie phased. The resulting
interference pattern enhances the signal in the required direction. A
very simple illustration is the variation of the strength of sound
from stereo speakers when one moves around, most noticeable when there
is a single tone on mono mode. The effect is magnified by multiple
elements to the extent that the ?beam? can be made very tight. The
more elements the better.
By adjusting the relative phase of the elements, the beam can be made
to swing over an arc, point in a particular direction or widen and
narrow as required. Often the array is actually a grid, allowing beam
control in two planes, usually up and down. It?s not just for
transmitting because the same effect also applies to the received
signal and sometimes the array is used solely for receiving, either
from a local active source or passively as a directable detector.
Though the management of the signal gets pretty complicated for big,
precise arrays, there are benefits other than simply the dispensing
with mechanical systems. They can be made to react very fast, and the
sensitivity and signal to noise ratio improves because the signal is
coherent whilst noise is random. You probably own a crude phased array
BTW, multi-element TV aerials reinforce the signal in the preferred
direction because the elements resonate in sympathy, narrowing and
extending the reception path. |
