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Phased-array radar systems are important
instruments in national electronic defense strategies. From the large, ship-based
systems that scan for distantly launched missiles to the more compact arrays installed
on fighter aircraft and unmanned aerial vehicles (UAVs), electronic phased-array
radars come in many sizes and forms, providing reliable signal detection and identification.
These modern systems offer many advantages over earlier radar systems that relied
on the physical movement of an antenna to steer a radar beam in search of a target.
This earlier method is certainly proven and reliable, having been used in military
platforms and commercial aviation for over 70 years, but it is limited in scan rate
by the mechanical motion of the antenna. In contrast, a phased-array radar system
uses many equally spaced antenna elements with phase shifters, with each element
contributing a small amount of electromagnetic (EM) radiation to form a much larger
beam. As the phase of each antenna element is shifted and aligned, the direction
of the radar beam changes and, as the amplitude of each element is varied, the pattern
of the far-field response is shaped into the desired response. Thus, the overall
radar antenna beam can be steered without need of a mechanically rotated antenna.
Beam forming, which can be now performed by means of analog or digital control,
can take place at extremely high speeds, limited only by the switching speed of
electronic components.
The
benefits of phased-array radar systems far outweigh their limitations, thus accounting
for their growing use in many military electronic systems and platforms. Since beam
steering in phased arrays can be performed at millisecond and faster speeds, the
signal can jump from one target to the next very quickly, while frequency agility
can be used to search quickly across a sector for targets. The coverage of a phased-array
antenna beam is typically limited to a 120-deg. sector in azimuth and elevation.
While this response is a known limitation of phased arrays, mechanically scanned
radar systems also have limitations in the physical area available for the motion
of the antenna.