When President Ronald Reagan announced the plan for the Strategic
Defense Initiative in the 1980s, it was considered
revolutionary.
Reagan's idea was to create a
defensive system that would zap enemy ballistic missiles aimed
at the U.S. before they got near us. Reagan's announcement implied
the use of novel technologies, including sophisticated radars
capable beyond anything in existence at the time.
Well, Naval Research Laboratory
scientists are working to bring the equally revolutionary dynamics
of plasma physics to the world of military radar -- and perhaps
beyond.
Meet Agile Mirror, which is quite
possibly a part of the radar of the future and is being developed
at NRL's Plasma Physics Division in collaboration with the Radar
Division.
Agile Mirror consists of a plasma
sheet formed in a low-pressure chamber by a gas discharge, explained
Dr. Robert Meger, Head of the Charged Particle Physics Branch,
Plasma Physics Division at NRL and principal investigator. The
present laboratory version measures 60 centimeters by 60 centimeters
by one centimeter. The plasma acts just like a conducting metal
sheet to the microwaves. It is possible to turn the plasma mirror
on and off very rapidly (less than 10 microseconds) and change
the orientation of the mirror in between pulses. Multiple high
power microwave sources with the same or different frequencies
could be combined on a single Agile Mirror, in sequence or
simultaneously.
"Its beauty is that it can
enable a radar system to follow many independent targets while
continuing to search for others," Dr. Meger said.
Agile Mirror, currently in an
experimental configuration, is a thing of visual beauty and awesome
potential.
Its broad-band capability will
enable variable or multifrequency radars as well as use for electronic
warfare, telemetry and communications. Moreover, it and related
technologies are potentially applicable to a variety of other
than military purposes, including weather detection (searching
for microbursts, for example), air-traffic control, telecommunications,
discharge lighting, and even pollution control.
But the people developing the
plasma mirror have a more immediate use in mind -- aboard U.S.
Navy ships and aircraft tracking multiple, high-velocity targets,
said Dr. Meger.
The plasma mirror, called Agile
Mirror because of its ability to change direction rapidly and
repeatedly, is a multipurpose, microwave beam director. It represents
advantages over existing radar technology including size, weight
and cost, but especially electronic steering, wide bandwidth
operation, and high power capability, he said.
"Because the plasma mirror
is electronically steerable with no moving parts, it possesses
the ability to more very fast from one point to another,"
Dr. Meger said.
Dr. Meger explained that radar
redirection (crucial for finding targets) originally depended
on moving antennas mechanically. This limited response time.
A substantial improvement in response time was achieved with
phased arrays, which are used on Aegis cruisers.
Phased array radar, which moves
electronically by changing the relative phase of individual elements
of the array, is costly and has frequency limitations. Frequencies
are important because a target invisible in one frequency may
be readily visible in another, Dr. Meger explained.
Agile Mirror differs significantly
because it offers a means of electronically directing single-element,
high-power, high-frequency microwave beams to a target.
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